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Java Coding Practice

What kind of Java practice exercises are there?

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In Java programming, commands are essential instructions that tell the computer what to do. These commands are written in a specific way so the computer can understand and execute them. Every program in Java is a set of commands. At the beginning of your Java programming practice , it’s good to know a few basic principles:

• In Java, each command ends with a semicolon;
• A command can't exist on its own: it’s a part of a method, and method is part of a class;
• Method (procedure, function) is a sequence of commands. Methods define the behavior of an object.

Here is an example of the command:

The command System.out.println("Hello, World!"); tells the computer to display the text inside the quotation marks.

If you want to display a number and not text, then you do not need to put quotation marks. You can simply write the number. Or an arithmetic operation. For example:

Command to display the number 1.

A command in which two numbers are summed and their sum (10) is displayed.

As we discussed in the basic rules, a command cannot exist on its own in Java. It must be within a method, and a method must be within a class. Here is the simplest program that prints the string "Hello, World!".

We have a class called HelloWorld , a method called main() , and the command System.out.println("Hello, World!") . You may not understand everything in the code yet, but that's okay! You'll learn more about it later. The good news is that you can already write your first program with the knowledge you've gained.

Attention! You can add comments in your code. Comments in Java are lines of code that are ignored by the compiler, but you can mark with them your code to make it clear for you and other programmers.

Single-line comments start with two forward slashes (//) and end at the end of the line. In example above we have a comment //here we print the text out

You can read the theory on this topic here , here , and here . But try practicing first!

Explore the Java coding exercises for practicing with commands below. First, read the conditions, scroll down to the Solution box, and type your solution. Then, click Verify (above the Conditions box) to check the correctness of your program.

The two main types in Java are String and int. We store strings/text in String, and integers (whole numbers) in int. We have already used strings and integers in previous examples without explicit declaration, by specifying them directly in the System.out.println() operator.

In the first case “I am a string” is a String in the second case 5 is an integer of type int. However, most often, in order to manipulate data, variables must be declared before being used in the program. To do this, you need to specify the type of the variable and its name. You can also set a variable to a specific value, or you can do this later. Example:

Here we declared a variable called a but didn't give it any value, declared a variable b and gave it the value 5 , declared a string called s and gave it the value Hello, World!

Attention! In Java, the = sign is not an equals sign, but an assignment operator. That is, the variable (you can imagine it as an empty box) is assigned the value that is on the right (you can imagine that this value was put in the empty box).

We created an integer variable named a with the first command and assigned it the value 5 with the second command.

Before moving on to practice, let's look at an example program where we will declare variables and assign values to them:

In the program, we first declared an int variable named a but did not immediately assign it a value. Then we declared an int variable named b and "put" the value 5 in it. Then we declared a string named s and assigned it the value "Hello, World!" After that, we assigned the value 2 to the variable a that we declared earlier, and then we printed the variable a, the sum of the variables a and b, and the variable s to the screen

This program will display the following:

We already know how to print to the console, but how do we read from it? For this, we use the Scanner class. To use Scanner, we first need to create an instance of the class. We can do this with the following code:

Once we have created an instance of Scanner, we can use the next() method to read input from the console or nextInt() if we should read an integer.

The following code reads a number from the console and prints it to the console:

Here we first import a library scanner, then ask a user to enter a number. Later we created a scanner to read the user's input and print the input out.

This code will print the following output in case of user’s input is 5:

More information about the topic you could read here , here , and here .

See the exercises on Types and keyboard input to practice Java coding:

Conditions and If statements in Java allow your program to make decisions. For example, you can use them to check if a user has entered a valid password, or to determine whether a number is even or odd. For this purpose, there’s an 'if/else statement' in Java.

The syntax for an if statement is as follows:

Here could be one or more conditions in if and zero or one condition in else.

Here's a simple example:

In this example, we check if the variable "age" is greater than or equal to 18. If it is, we print "You are an adult." If not, we print "You are a minor."

Here are some Java practice exercises to understand Conditions and If statements:

In Java, a "boolean" is a data type that can have one of two values: true or false. Here's a simple example:

The output of this program is here:

In addition to representing true or false values, booleans in Java can be combined using logical operators. Here, we introduce the logical AND (&&) and logical OR (||) operators.

• && (AND) returns true if both operands are true. In our example, isBothFunAndEasy is true because Java is fun (isJavaFun is true) and coding is not easy (isCodingEasy is false).
• || (OR) returns true if at least one operand is true. In our example, isEitherFunOrEasy is true because Java is fun (isJavaFun is true), even though coding is not easy (isCodingEasy is false).
• The NOT operator (!) is unary, meaning it operates on a single boolean value. It negates the value, so !isCodingEasy is true because it reverses the false value of isCodingEasy.

So the output of this program is:

More information about the topic you could read here , and here .

Here are some Java exercises to practice booleans:

With loops, you can execute any command or a block of commands multiple times. The construction of the while loop is:

Loops are essential in programming to execute a block of code repeatedly. Java provides two commonly used loops: while and for.

1. while Loop: The while loop continues executing a block of code as long as a specified condition is true. Firstly, the condition is checked. While it’s true, the body of the loop (commands) is executed. If the condition is always true, the loop will repeat infinitely, and if the condition is false, the commands in a loop will never be executed.

In this example, the code inside the while loop will run repeatedly as long as count is less than or equal to 5.

2. for Loop: The for loop is used for iterating a specific number of times.

In this for loop, we initialize i to 1, specify the condition i <= 5, and increment i by 1 in each iteration. It will print "Count: 1" to "Count: 5."

Here are some Java coding challenges to practice the loops:

An array in Java is a data structure that allows you to store multiple values of the same type under a single variable name. It acts as a container for elements that can be accessed using an index.

What you should know about arrays in Java:

• Indexing: Elements in an array are indexed, starting from 0. You can access elements by specifying their index in square brackets after the array name, like myArray[0] to access the first element.
• Initialization: To use an array, you must declare and initialize it. You specify the array's type and its length. For example, to create an integer array that can hold five values: int[] myArray = new int[5];
• Populating: After initialization, you can populate the array by assigning values to its elements. All elements should be of the same data type. For instance, myArray[0] = 10; myArray[1] = 20;.
• Default Values: Arrays are initialized with default values. For objects, this is null, and for primitive types (int, double, boolean, etc.), it's typically 0, 0.0, or false.

In this example, we create an integer array, assign values to its elements, and access an element using indexing.

In Java, methods are like mini-programs within your main program. They are used to perform specific tasks, making your code more organized and manageable. Methods take a set of instructions and encapsulate them under a single name for easy reuse. Here's how you declare a method:

• public is an access modifier that defines who can use the method. In this case, public means the method can be accessed from anywhere in your program.Read more about modifiers here .
• static means the method belongs to the class itself, rather than an instance of the class. It's used for the main method, allowing it to run without creating an object.
• void indicates that the method doesn't return any value. If it did, you would replace void with the data type of the returned value.

In this example, we have a main method (the entry point of the program) and a customMethod that we've defined. The main method calls customMethod, which prints a message. This illustrates how methods help organize and reuse code in Java, making it more efficient and readable.

In this example, we have a main method that calls the add method with two numbers (5 and 3). The add method calculates the sum and returns it. The result is then printed in the main method.

All composite types in Java consist of simpler ones, up until we end up with primitive types. An example of a primitive type is int, while String is a composite type that stores its data as a table of characters (primitive type char). Here are some examples of primitive types in Java:

• int: Used for storing whole numbers (integers). Example: int age = 25;
• double: Used for storing numbers with a decimal point. Example: double price = 19.99;
• char: Used for storing single characters. Example: char grade = 'A';
• boolean: Used for storing true or false values. Example: boolean isJavaFun = true;
• String: Used for storing text (a sequence of characters). Example: String greeting = "Hello, World!";

Simple types are grouped into composite types, that are called classes. Example:

We declared a composite type Person and stored the data in a String (name) and int variable for an age of a person. Since composite types include many primitive types, they take up more memory than variables of the primitive types.

See the exercises for a coding practice in Java data types:

String is the most popular class in Java programs. Its objects are stored in a memory in a special way. The structure of this class is rather simple: there’s a character array (char array) inside, that stores all the characters of the string.

String class also has many helper classes to simplify working with strings in Java, and a lot of methods. Here’s what you can do while working with strings: compare them, search for substrings, and create new substrings.

Example of comparing strings using the equals() method.

Also you can check if a string contains a substring using the contains() method.

You can create a new substring from an existing string using the substring() method.

More information about the topic you could read here , here , here , here , and here .

Here are some Java programming exercises to practice the strings:

In Java, objects are instances of classes that you can create to represent and work with real-world entities or concepts. Here's how you can create objects:

First, you need to define a class that describes the properties and behaviors of your object. You can then create an object of that class using the new keyword like this:

It invokes the constructor of a class.If the constructor takes arguments, you can pass them within the parentheses. For example, to create an object of class Person with the name "Jane" and age 25, you would write:

Suppose you want to create a simple Person class with a name property and a sayHello method. Here's how you do it:

In this example, we defined a Person class with a name property and a sayHello method. We then created two Person objects (person1 and person2) and used them to represent individuals with different names.

Here are some coding challenges in Java object creation:

Static classes and methods in Java are used to create members that belong to the class itself, rather than to instances of the class. They can be accessed without creating an object of the class.

Static methods and classes are useful when you want to define utility methods or encapsulate related classes within a larger class without requiring an instance of the outer class. They are often used in various Java libraries and frameworks for organizing and providing utility functions.

You declare them with the static modifier.

Static Methods

A static method is a method that belongs to the class rather than any specific instance. You can call a static method using the class name, without creating an object of that class.

In this example, the add method is static. You can directly call it using Calculator.add(5, 3)

Static Classes

In Java, you can also have static nested classes, which are classes defined within another class and marked as static. These static nested classes can be accessed using the outer class's name.

In this example, Student is a static nested class within the School class. You can access it using School.Student.

More information about the topic you could read here , here , here , and here .

See below the exercises on Static classes and methods in our Java coding practice for beginners:

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Java Solved Programs and Problems with Solutions

Discover a comprehensive collection of solved Java programs and problems with step-by-step solutions. Elevate your Java programming skills by exploring practical examples and effective problem-solving techniques. From sorting algorithms to data structures, gain hands-on experience and sharpen your Java expertise. Start solving Java challenges today and level up your programming prowess.

Solve a real-world problem using Java

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As I wrote in the first two articles in this series, I enjoy solving small problems by writing small programs in different languages, so I can compare the different ways they approach the solution. The example I'm using in this series is dividing bulk supplies into hampers of similar value to distribute to struggling neighbors in your community, which you can read about in the first article in this series.

In the first article, I solved this problem using the Groovy programming language , which is like Python in many ways, but syntactically it's more like C and Java. In the second article, I solved it in Python with a very similar design and effort, which demonstrates the resemblance between the languages.

Now I'll try it in Java .

The Java solution

When working in Java, I find myself declaring utility classes to hold tuples of data (the new record feature is going to be great for that), rather than using the language support for maps offered in Groovy and Python. This is because Java encourages creating maps that map one specific type to another specific type, but in Groovy or Python, it's cool to have a map with mixed-type keys and mixed-type values.

The first task is to define these utility classes, and the first is the Unit class:

There's nothing too startling here. I effectively created a class whose instances are immutable since there are no setters for fields item , brand , or price and they are declared private . As a general rule, I don't see value in creating a mutable data structure unless I'm going to mutate it; and in this application, I don't see any value in mutating the Unit class.

While more effort is required to create these utility classes, creating them encourages a bit more design effort than just using a map, which can be a good thing. In this case, I realized that a bulk package is composed of a number of individual units, so I created the Pack class:

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Similar to the Unit class, the Pack class is immutable. A couple of things worth mentioning here:

• I could have passed a Unit instance into the Pack constructor. I chose not to because the bundled, physical nature of a bulk package encouraged me to think of the "unit-ness" as an internal thing not visible from the outside but that requires unpacking to expose the units. Is this an important decision in this case? Probably not, but to me, at least, it's always good to think through this kind of consideration.
• Which leads to the unpack() method. The Pack class creates the list of Unit instances only when you call this method—that is, the class is lazy . As a general design principle, I've found it's worthwhile to decide whether a class' behavior should be eager or lazy, and when it doesn't seem to matter, I go with lazy. Is this an important decision in this case? Maybe—this lazy design enables a new list of Unit instances to be generated on every call of unpack() , which could prove to be a good thing down the road. In any case, getting in the habit of always thinking about eager vs. lazy behavior is a good habit.

The sharp-eyed reader will note that, unlike in the Groovy and Python examples where I was mostly focused on compact code and spent way less time thinking about design decisions, here, I separated the definition of a Pack from the number of Pack instances purchased. Again, from a design perspective, this seemed like a good idea as the Pack is conceptually quite independent of the number of Pack instances acquired.

Given this, I need one more utility class: the Bought class:

• I decided to pass a Pack into the constructor. Why? Because to my way of thinking, the physical structure of the purchased bulk packages is external, not internal, as in the case of the individual bulk packages. Once again, it may not be important in this application, but I believe it's always good to think about these things. If nothing else, note that I am not married to symmetry!
• Once again the unpack() method demonstrates the lazy design principle. This goes to more effort to generate a list of Unit instances (rather than a list of lists of Unit instances, which would be easier but require flattening further out in the code).

OK! Time to move on and solve the problem. First, declare the purchased packs:

This is pretty nice from a readability perspective: there is one pack of Best Family Rice containing 10 units that cost 5,650 (using those crazy monetary units, like in the other examples). It's straightforward to see that in addition to the one bulk pack of 10 bags of rice, the organization acquired 10 bulk packs of one bag each of spaghetti. The utility classes are doing some work under the covers, but that's not important at this point because of the great design job!

Note the var keyword is used here; it's one of the nice features in recent versions of Java that help make the language a bit less verbose (the principle is called DRY —don't repeat yourself) by letting the compiler infer the variable's data type from the right-side expression's type. This looks kind of similar to the Groovy def keyword, but since Groovy by default is dynamically typed and Java is statically typed, the typing information inferred in Java by var persists throughout the lifetime of that variable.

Finally, it's worth mentioning that packs here is an array and not a List instance. If you were reading this data from a separate file, you would probably prefer to create it as a list.

Next, unpack the bulk packages. Because the unpacking of Pack instances is delegated into lists of Unit instances, you can use that like this:

This uses some of the nice functional programming features introduced in later Java versions. Convert the array packs declared previously to a Java stream, use flatmap() with a lambda to flatten the sublists of units generated by the unpack() method of the Bought class, and collect the resulting stream elements back into a list.

As in the Groovy and Java solutions, the final step is repacking the units into the hampers for distribution. Here's the code—it's not much wordier than the Groovy version (tiresome semicolons aside) nor really all that different:

Some clarification, with numbers in brackets in the comments above (e.g., [1] ) corresponding to the clarifications below:

• 1. Set up the ideal and maximum values to be loaded into any given hamper, initialize Java's random number generator and the hamper number.
• 2.1 Increment the hamper number, get a new empty hamper (a list of Unit instances), and set its value to 0.
• 2.2.1 Get a random number between zero and the number of remaining units minus 1.
• 2.2.2 Assume you can't find more units to add.
• 2.2.3.1 Figure out which unit to look at.
• 2.2.3.2 Add this unit to the hamper if there are only a few left or if the value of the hamper isn't too high once the unit is added and that unit isn't already in the hamper.
• 2.2.3.3 Add the unit to the hamper, increment the hamper value by the unit price, and remove the unit from the available units list.
• 2.2.3.4 As long as there are units left, you can add more, so break out of this loop to keep looking.
• 2.2.4 On exit from this for {} loop, if you inspected every remaining unit and could not find one to add to the hamper, the hamper is complete; otherwise, you found one and can continue looking for more.
• 2.3 Print out the contents of the hamper.
• 2.4 Print out the remaining units info.

When you run this code, the output looks quite similar to the output from the Groovy and Python programs:

The last hamper is abbreviated in contents and value.

Closing thoughts

The similarities in the "working code" with the Groovy original are obvious—the close relationship between Groovy and Java is evident. Groovy and Java diverged in a few ways in things that were added to Java after Groovy was released, such as the var vs. def keywords and the superficial similarities and differences between Groovy closures and Java lambdas. Moreover, the whole Java streams framework adds a great deal of power and expressiveness to the Java platform (full disclosure, in case it's not obvious—I am but a babe in the Java streams woods).

Java's intent to use maps for mapping instances of a single type to instances of another single type pushes you to use utility classes, or tuples, instead of the more inherently flexible intents in Groovy maps (which are basically just Map<Object,Object> plus a lot of syntactic sugar to vanish the kinds of casting and instanceof hassles that you would create in Java) or in Python. The bonus from this is the opportunity to apply some real design effort to these utility classes, which pays off at least insofar as it instills good habits in the programmer.

Aside from the utility classes, there isn't a lot of additional ceremony nor boilerplate in the Java code compared to the Groovy code. Well, except that you need to add a bunch of imports and wrap the "working code" in a class definition, which might look like this:

The same fiddly bits are necessary in Java as they are in Groovy and Python when it comes to grabbing stuff out of the list of Unit instances for the hampers, involving random numbers, loops through remaining units, etc.

Another issue worth mentioning—this isn't a particularly efficient approach. Removing elements from ArrayLists , being careless about repeated expressions, and a few other things make this less suitable for a huge redistribution problem. I've been a bit more careful here to stick with integer data. But at least it's quite quick to execute.

Yes, I'm still using the dreaded while { … } and for { … } . I still haven't thought of a way to use map and reduce style stream processing in conjunction with a random selection of units for repackaging. Can you?

Stay tuned for the next articles in this series, with versions in Julia and Go .

Why I use Java

There are probably better languages than Java, depending on work requirements. But I haven't seen anything yet to pull me away.

Managing a non-profit organization's supply chain with Groovy

Let's use Groovy to solve a charity's distribution problem.

Use Python to solve a charity's business problem

Comparing how different programming languages solve the same problem is fun and instructive. Next up, Python.

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Web Development

How to improve problem solving skills in java programming.

Most developers would agree that Java problem solving skills are one of the most important skills to have when it comes to programming. After all, what good is a developer who can’t solve problems? But even for the best Java developers, problem solving skills in Java programming can be a difficult task.

That’s why we’ve put together this list of 6 easy tips to improve problem solving skills in programming (Java).

What Do We Mean By Programming Problem Solving Skills?

Problem solving skills are the ability to identify and solve problems. When it comes to Java development, this means being able to find solutions to coding challenges, debugging errors, and working through difficult logic puzzles.

Java Problem Solving For Beginners (With An Example):

Let’s take a look at an example of how to use problem-solving skills in Java. Suppose you have a list of numbers, and you want to find the sum of the even numbers in that list. This is what your code might look like:

In this code, we are using a for loop to iterate through the list of numbers. We then use a conditional statement to determine if the integer passed to the conditional statement is even or not. If it is an even number, we add it to our sum variable.

Here’s how you would solve this problem without using any of the available tools in Java:

Use a for loop to iterate through each number in your list. Use modulus (%) and double-check your work to make sure that you know which numbers are even.

With a for loop, this might not look too difficult. But what happens when the problem gets more complex? What happens when you have a list of 100 or 1000 numbers instead of just 6? You would have to use nested for loops, and it could get very confusing.

Why Is Learning Problem Solving Skills In Java So Crucial?

While having adequate skills in problem-solving, Java developers can create ample amount of opportunities for themselves, like:

• They can meet the high demand for Java developers and command high salaries.
• They can ace software engineering, as problem solving is a critical skill for any software engineer.
• They can get support from the largest development communities in the world.

How To Improve Problem Solving Skills In Competitive Programming:

1. practice makes perfect with skills of problem solving.

The only way to get better at solving problems is by practicing. The more complex the situation, the more you will need to rely on your problem solving skills and ability to think outside the box. If you’re one of those developers that are always looking for a challenge, take online boot camps where companies post coding challenges and Java programmers compete against each other to find solutions as quickly as possible.

2. Use the Power of Google (or other dev tools)

There may be times when your code works perfectly fine but you still don’t know how it actually works. When you run into these times, don’t be afraid to use Google! There are times when a simple Google search is all you need to complete the task at hand.

3. Find a Friend for Code Reviews

If you have a colleague or friend who’s also passionate about Java development, find them and do code reviews together! Code reviews are an excellent learning experience for any developer. Not only will they help improve your skills of problem solving in Java, but they will also teach you new things that you might not know about the language.

4. Try Pair Programming

Pair programming is a great way to work through bugs and complex logic problems with another person. When coding in pairs, it becomes much easier to solve difficult problems since there are two brains working on it—and if one of those programmers knows how to solve the problem, the other one might just learn something new.

Read the Related Article – what is pair programming ?

5. Use Debuggers to Your Advantage

Debuggers are a developer’s best friend—they will save you time and headaches when it comes to debugging errors in code. If you don’t have any experience with Java debuggers, now would be a great time to try one out! Just knowing how to use a debugger can go a long way in helping you solve difficult problems.

6. Keep an Open Mind

When solving a problem, there will be some developers who try to use the “standard” way of doing things. For some problems, this might work perfectly fine—but when you’re trying to solve a difficult problem, sometimes it’s best not to follow convention and think outside the box!

Being able to solve problems is one of the essential web developer skills , but Java developers, in particular, need strong skills in problem-solving to succeed. If you’re looking for help with how to improve your problem solving abilities in Java, start by practicing more often and using the power of Google or other dev tools when needed. You can also find friends who are passionate about programming to do code reviews together—or if you want some hands-on experience try pair programming! Debuggers will save time and headaches as well, so make sure that you know how they work before tackling difficult problems on your own. The key is practice; give these tips a shot today and see what happens!

Ans- Skills of Problem solving in Java are the ability to identify and solve problems. This includes being able to understand the problem, come up with a solution, and then code that solution. Java developers need these skills to be successful because they often have to work on projects with tight deadlines and limited resources.

Ans- The best time to use Google is when a developer doesn’t know how to solve a problem that they’re facing. There’s almost always someone who has run into the same problem, so it’s important to know how to use Google to find other solutions.

Ans- Pair programming is a method of working on a task with another person. One developer codes while the other reviews, and together they work through the problem. It’s a great way to learn while you work, and it can be especially helpful for more difficult problems that require the knowledge of both developers.

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• Output of Java program | Set 16 (Threads)

In computing, the producer-consumer problem (also known as the bounded-buffer problem) is a classic example of a multi-process synchronization problem. The problem describes two processes, the producer and the consumer, which share a common, fixed-size buffer used as a queue. 

• The producer’s job is to generate data, put it into the buffer, and start again.
• At the same time, the consumer is consuming the data (i.e. removing it from the buffer), one piece at a time.

Problem   To make sure that the producer won’t try to add data into the buffer if it’s full and that the consumer won’t try to remove data from an empty buffer.

Solution  The producer is to either go to sleep or discard data if the buffer is full. The next time the consumer removes an item from the buffer, it notifies the producer, who starts to fill the buffer again. In the same way, the consumer can go to sleep if it finds the buffer to be empty. The next time the producer puts data into the buffer, it wakes up the sleeping consumer.  An inadequate solution could result in a deadlock where both processes are waiting to be awakened.  Recommended Reading- Multithreading in JAVA , Synchronized in JAVA , Inter-thread Communication

Implementation of Producer Consumer Class  

• A LinkedList list – to store list of jobs in queue.
• A Variable Capacity – to check for if the list is full or not
• A mechanism to control the insertion and extraction from this list so that we do not insert into list if it is full or remove from it if it is empty.

Note: It is recommended to test the below program on a offline IDE as infinite loops and sleep method may lead to it time out on any online IDE   

Output:  

Important Points   

• In PC class (A class that has both produce and consume methods), a linked list of jobs and a capacity of the list is added to check that producer does not produce if the list is full.
• Also, we have an infinite outer loop to insert values in the list. Inside this loop, we have a synchronized block so that only a producer or a consumer thread runs at a time.
• An inner loop is there before adding the jobs to list that checks if the job list is full, the producer thread gives up the intrinsic lock on PC and goes on the waiting state.
• If the list is empty, the control passes to below the loop and it adds a value in the list.
• Inside, we also have an inner loop which checks if the list is empty.
• If it is empty then we make the consumer thread give up the lock on PC and passes the control to producer thread for producing more jobs.
• If the list is not empty, we go round the loop and removes an item from the list.
• In both the methods, we use notify at the end of all statements. The reason is simple, once you have something in list, you can have the consumer thread consume it, or if you have consumed something, you can have the producer produce something.
• sleep() at the end of both methods just make the output of program run in step wise manner and not display everything all at once so that you can see what actually is happening in the program.

Exercise :  

• Readers are advised to use if condition in place of inner loop for checking boundary conditions.
• Try to make your program produce one item and immediately after that make the consumer consume it before any other item is produced by the producer.

Reference – https://en.wikipedia.org/wiki/Producer%E2%80%93consumer_problem

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Top 20 Java coding interview questions for 2024

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From your first line of code, to your first day on the job — Educative has you covered. Join 2M+ developers learning in-demand programming skills.

Coding interviews are aimed at gauging how well-prepared a candidate is in terms of language proficiency, foundational knowledge, problem-solving skills, and soft skills. For a position that explicitly mentions a language, such as a job listing for a Java developer, it makes even more sense to spend some time and energy polishing Java skills by exploring the common interview questions asked in such interviews. Doing this not only allows us to benefit directly from the experience of others but more importantly, it’s an opportunity to learn things that we are not aware are gaps in our knowledge.

Java interview questions

In this blog, we cover 20 Java language-specific interview questions on a variety of topics. We’re also including answers to these questions to help you prepare for them. For more interview questions, check out the links at the end of this blog.

16. What’s an anonymous class?

An anonymous class is a nested class that has no name and is defined and instantiated all at once. For this reason, an anonymous class can be instantiated only once. Note that an anonymous class is used to either extend another class or implement an interface. To create an anonymous class instance, the new operator is applied to the name of its superclass or the name of the interface being implemented, as shown on lines 11–23 in the widget below.

17. What’s the difference between an iterable and an iterator?

An iterable is an object that implements the Iterable interface. All Java collections implement this interface. This enables us to iterate over these collections using an iterator returned by the iterator() method, as well as by using the forEach() method.

An iterator , on the other hand, is an object that implements the Iterator interface. It supports the hasNext() method which can be used for checking if there is a non-null element at the next position in the collection. If the element exists, it can be retrieved using the next() method. It also supports the remove() method, which can be used for safely removing an element from the iterable during the iteration. The element removed is the same as the one returned by the previous call to next() . The following code shows how these methods can be used on lines 15–18 .

Note that when an iterator is in use, direct additions or removals from a collection can result in a ConcurrentModificationException exception being thrown. The iterators that implement this behavior are called fail-fast iterators .

18. What’s the difference between a HashMap and a TreeMap ?

Both are Java collections used for storing key-value pairs. Internally, the HashMap class is implemented like a hash table, but the TreeMap class is implemented as a red-black tree, which is a balanced binary search tree. So retrieval, addition, and checking for containment of an element is O ( 1 ) O(1) O ( 1 ) for HashMap vs. O ( log ⁡ n ) O(\log n) O ( lo g n ) for TreeMap . Searching is asymptotically the same at O ( log ⁡ n ) O(\log n) O ( lo g n ) for both.

On the other hand, a tree map has a distinct advantage over a hash map in that the keys stored in it are ordered, and if an application has a need for ordering data, then it’s a better fit. The order in which the keys are stored is said to be the natural order and is specified by the implementation of compareTo in the Comparable interface. By default, the numeric keys in a tree map are stored under the usual ordering on the set of real numbers. Keys that are strings are ordered alphabetically.

The following example shows a few method calls that retrieve ordered data from a tree map.

19. What purpose does the synchronized keyword serve?

The synchronized keyword is applied to code blocks or methods to ensure that each such code block can be executed by only one thread at a time. Each code block is synchronized over an object shown as follows:

The synchronized keyword can also be applied directly to a method name. In such a case, the method is synchronized on the this object. For instance, in the following code, the increment() method defined on lines 6–16 is synchronized on the this object.

A thread that enters the code of one of the synchronized methods has the lock over the this object, and all other threads are blocked from entering and executing any method or code block synchronized on the same object.

Once the thread holding the lock exits the code block, the lock over the object is released.

If we remove the synchronized keyword from line 6 , we note that in one execution (see below), the first thread prints 0 Ping , then the second thread prints 0 Pong , followed by the first thread printing 2 Ping . The fact that 0 was printed twice and 1 was never printed indicates that the threads were switched while increment() was still being executed.

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Solve any number patterns programs in Java

• Categories Java , Iterative Statements , Nested loops

Watch our video on How to solve any number pattern program in Java – Click Here

1. write a python program to print following number pattern: .

   1    2 2    3 3 3    4 4 4 4    5 5 5 5 5

2. Write a python program to print following pattern: 

  5   4 4   3 3 3   2 2 2 2   1 1 1 1 1

3. Write a python code to print following number pattern: 

  0   2 2   4 4 4   6 6 6 6   8 8 8 8 8

Code:       

4. Write a python code to print following pattern: 

  1   2 2   1 1 1   2 2 2 2   1 1 1 1 1

5. Write a python program to print following Dimond number pattern: 

                  1               2 2 2           3 3 3 3 3       4 4 4 4 4 4 4    5 5 5 5 5 5 5 5 5       6 6 6 6 6 6 6           7 7 7 7 7             8 8 8                 9

6. Write a python program to print following diamond number pattern: 

                  1                2 2 2             3 3 3 3 3         4 4 4 4 4 4 4      5 5 5 5 5 5 5 5 5        4 4 4 4 4 4 4            3 3 3 3 3               2 2 2                  1

7. Write a python program to print number pattern: 

   1     1 2    1 2 3    1 2 3 4    1 2 3 4 5

8. Write a python code to print following number pattern: 

  1 2 3 4 5      1 2 3 4         1 2 3            1 2               1

9. Write a python code to print following number hill pattern: 

                1              1 2 3           1 2 3 4 5       1 2 3 4 5 6 7    1 2 3 4 5 6 7 8 9

10. Write a python code to print following number pattern : 

  5   5 4   5 4 3   5 4 3 2   5 4 3 2 1

11. Write a python code to print following number pattern : 

  5 4 3 2 1      4 3 2 1         3 2 1            2 1               1

12. Write a python code to print hill pattern with numbers : 

                1              1 2 1           1 2 3 2 1        1 2 3 4 3 2 1     1 2 3 4 5 4 3 2 1

13. Write a python code to print following number pattern : 

  1   2 3   4 5 6   7 8 9 10

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More From Forbes

How tech teams go analog to solve business problems.

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To help its tech team stay innovative, online catering leader ezCater uses in-person improve ... [+] sessions.

One unexpected transformation that came out of the pandemic is the dramatic change in how companies serve lunch. Gone are the days when the company cafeteria was the place to mingle with colleagues, grab a working lunch with the team or pop in for a between-meeting coffee.

In the new world of hybrid and remote work, companies no longer see the financial sense of feeding employees three meals a day on a broad scale. With the on-site employee cafeteria obsolete, companies are challenged with how to provide the now-expected meals to employees without considerable waste.

Enter ezCater , an online catering platform that provides meals for clients that range from Rice University to the San Francisco Giants baseball franchise. Its innovations include not only custom meals for groups of all sizes, but also ordering from local restaurants , which supports local economies, and an app where individuals can each order from the restaurant of their choice to achieve the customization not available during the cafeteria days.

On its way to becoming the source for post-covid companies to order lunch for employees, one tech leader embraced an analog methodology to drive innovative thinking. Curious about how innovators stay innovative, I caught up with Erin DeCesare, chief technology officer of ezCater.

To keep her team’s thinking fresh, DeCesare brought in a distinctly non-tech approach to problem solving: improv.

Once the bastion of comedy clubs and acting classes, improv has migrated into the world of business to help build creative muscle in a way that’s fun and engaging. In a workplace where most employees are glued to their laptops for the majority of their days, bringing improv into the mix has been an exercise in creative thinking and innovative problem solving.

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Taking the process a step beyond the traditional team building exercises, ezCater’s Chief Technology Officer Erin DeCesare introduced a weekly gathering to help address challengess and bring fresh thinking to the group.

“My engineers were super skeptical at first, but then they had so much fun and it drove up the energy level,” said DeCesare. “The idea of exposing half-baked ideas was uncomfortable at first. They want to come up with the perfect answer.”

Getting comfortable with the discomfort, and inviting a sense of play, are two keys for successful sessions. If you want to bring a more innovative mindset to your team, here are a few things to consider.

Set The Right Tone

"The most important factor is creating a safe environment for half-baked ideas," DeCesare says. "Leave judgement at the door and make it clear this is an experiment where there are no mistakes."

Tech people want to be absolutely accurate and are uncomfortable with making mistakes in front of each other. DeCesare reframed the process as “learning sprints” designed to explore new ideas without having the answer right away.

Expand Thinking About Resources

Sometimes people limit their thinking because they don’t have the right information or resources. DeCesare invites the team to imagine they are in a “magic room” with leaders who can give them what they need to move ideas forward, or outside industry experts can help. This introduces the idea of which new questions might lead them to a solution.

Make The Problem Personal

"People naturally become more engaged when they can relate the issue to real situations and experiences," said DeCesare. Having the problem presenter share the human context and struggle allows others to empathize and ideate more freely. Invite your team members to share their individual experiences working the problem rather than presenting a data dump.

End With Commitments

While divergent thinking is valuable to idea generation, DeCesare stresses the importance of “closing the scene” to bring resolution to a specific session.

"Don't leave the improv session without specific next steps. Someone should rearticulate the potential solutions and volunteer to apply them over the next sprint." This brings closure and accountability, and makes people believe their time was well spent.

DeCesare points out that her team’s process took some experimenting to arrive at ongoing practice to create skills that deliver compelling solutions.

"Improv forces people to break out of their normal thinking patterns," said DeCesare. "But you have to be intentional about bridging that creativity back to real-world execution. The magic is in making it repeatable for your team's workflow."

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2024 Global Climate Challenge

How Can we get rid from Waterlogging Problem in a City?

Sayed Huzaifa Mumit

Our Organization

What is the name of your solution, provide a one-line summary of your solution..

Production of Methane Gas from Rainwater and Carbon dioxide

In what city, town, or region is your solution team headquartered?

In what country is your solution team headquartered, what type of organization is your solution team.

Not registered as any organization

What specific problem are you solving?

When it rains in Bangladesh many city areas go underwater and waterlogging in the streets. These cities are situated on the riverside. The project was conducted to solve this problem and to get benefits from the environment. The procedure was Collecting rainwater samples in a flask or large area requires separating pure water vapor in a balloon or any alternative container. Reduced heat, analogous to condensation, causes it to form liquid water. Now, need to separate hydrogen gas from water using the best method of electrolysis at an affordable cost. The production of hydrogen gas is one of the final products that produces methane gas. Now, pure carbon dioxide needs to be collected from any source in a wolf bottle or any other alternative container, like a flask. Collected hydrogen gas and carbon dioxide need to be mixed in a bottle. Mixed gases are called water gases, and where they need to provide heat, therefore, they become methane gas, and as a side product, water vapor is also produced. But when products need to decrease heat, like condensation, then methane gas will separate. The final product will grow the country’s economy by exporting and meeting the needs of citizens.

What is your solution?

The environment will also be balanced if carbon dioxide emissions decrease. Produced Methane gas can be utilized in manufacturing to drive or power motors and turbines. The energy released is used by industries such as pulp and paper, food processors, petroleum refineries, and firms that work with stone, clay, and glass. Businesses may use methane-based combustion to dry, dehumidify, melt, and clean their products. It is also utilized to generate energy for illumination. Some other countries where yearlong wet places exist have a great chance to use them. This country can grow their economy and also meet their mineral needs. Some Places in many countries are Emei Shan, Sichuan Province, China Average annual rainfall: is 8169mm. Kukui, Maui, HawaiiAverage annual rainfall: 9293mm.Mt Waialeale, Kauai, Hawaii Average annual rainfall: 9763mm. Etc.[c.1] It was easy to collect samples. But the large area will require a cost. The product can be profitable after being exported outside of the country. Water also produces methane, s

water can be recycled while rainwater can’t be collected. In the street when water together to make the project profitable and directly or indirectly increase the quality of life of the people for whom it was conducted. Here the graph shows the previous four years of data on the waterlogging road of Chittagong city in percent. The red dot shows a blocked road by rainwater, and the green dot shows an unblocked road. Graph 2: Here Climate chart of Chittagong city[c.2] Some data on air pollution by carbon of Chittagong, Bangladesh: The mission inventory of Chittagong city is 20 X 32 km2, with the pivot point at 377374.00 mE and 2472510.00 mN and cell resolution of 1x1 km2.The whole Chittagong City Corporation region, as well as sections of the Sitakunda, Hathhazari, Raozan, BoalKhali, Patiya, and Anowara Upazilas, are included.[9]

Who does your solution serve, and in what ways will the solution impact their lives?

In Bangladesh, many cities and towns go underwater during the rainy season. Bangladesh has a value geographically; it has 6 seasons, of which 3 are mostly rainy. Chittagong and Dhaka have a common waterlogging problem due to all the canals containing trash and pollution. If using the method or experiment explained above, we collect rainwater, purify it, and then produce methane gas, it can meet the demand of certain areas where people live in middle-class families, and after meeting the demand, we can export it outside Bangladesh. The cost of production will be lower than the procurement cost of methane from minerals.

How are you and your team well-positioned to deliver this solution?

My team Will contact the government and after getting permission then will contact the Industries that emit CO2. To Capture CO2 there will be a contract. 

Then talking with the municipality mayor about collecting the rainwater from the street where waterlogged. 

Both will bring a Factory and Use the procedure of the research to produce methane gas and distribute it to the nation.

Which dimension of the Challenge does your solution most closely address?

Which of the un sustainable development goals does your solution address.

• 3. Good Health and Well-Being
• 6. Clean Water and Sanitation
• 7. Affordable and Clean Energy
• 8. Decent Work and Economic Growth
• 9. Industry, Innovation, and Infrastructure
• 11. Sustainable Cities and Communities
• 13. Climate Action

What is your solution’s stage of development?

Please share details about why you selected the stage above..

I have developed the Model for solving specific cities and environmental disasters.

Production of Methane Gas from Rainwater caused unwantedly fro Climate changes By Carbon dioxide Emission.

Why are you applying to Solve?

It has several answers, 

The growth of the economy by exporting, To get rid of the people of the city. CIlmate changes or the disasters of nature to get rid.To meet the demand of the people.

In which of the following areas do you most need partners or support?

• Product / Service Distribution (e.g. delivery, logistics, expanding client base)
• Technology (e.g. software or hardware, web development/design)

Who is the Team Lead for your solution?

Solution team.

The Solve team will review your report and remove any inappropriate content.

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I have been solving the Project Euler Problem since 2021, most of problems have been solved using python, now I am going to solve again at the beginning of the problem set using JavaScript.

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Pave the Way for Self-regulation and Problem-solving With Social-emotional Learning

Posted: April 3, 2024

Problem-solving is a social-emotional learning (SEL) skill children need for lifelong success. Effective problem-solving skills support children's ability to self-regulate, focus on tasks, think flexibly and creatively, work with others, and generate multiple ways to solve problems. When young children develop and build these skills, it positively impacts their interactions with others, grows their capacity to manage challenges, and boosts a sense of competence.

A group of school-age children are stacking plastic blocks with an educator.

The foundation for effective social problem-solving is grounded in self-regulation, or the ability to regulate emotions when interacting with others. It is easier to focus on one's feelings and the feelings and perspectives of others and to work cooperatively toward solutions when a child can self-regulate and calm down. Children develop self-regulation skills over time, with practice and with adult guidance. Equally important is how an adult models emotion regulation and co-regulation. 

"Caregivers play a key role in cultivating the development of emotion regulation through co-regulation, or the processes by which they provide external support or scaffolding as children navigate their emotional experiences" (Paley & Hajal, 2022, p. 1).

When adults model calm and self-regulated approaches to problem-solving, it shows children how to approach problems constructively. For example, an educator says, "I'm going to take a breath and calm down so I can think better." This model helps children see and hear a strategy to support self-regulation.

Problem-solving skills help children resolve conflicts and interact with others as partners and collaborators. Developing problem-solving skills helps children learn and grow empathy for others, stand up for themselves, and build resilience and competence to work through challenges in their world. 

Eight strategies to support problem-solving 

• Teach about emotions and use feeling words throughout the day. When children have more words to express themselves and their feelings, it is easier to address and talk about challenges when they arise. 
• Recognize and acknowledge children's feelings throughout the day. For example, when children enter the classroom during circle time, mealtime, and outside time, ask them how they feel. Always acknowledge children's feelings, both comfortable and uncomfortable, to support an understanding that all feelings are OK to experience.  
• Differentiate between feelings and behaviors. By differentiating feelings from behaviors, educators contribute to children’s understanding that all feelings are OK, but not all behaviors are OK. For example, an educator says, "It looks like you may be feeling mad because you want the red blocks, and Nila is playing with them. It's OK to feel mad but not OK to knock over your friend’s blocks."
• Support children's efforts to calm down. When children are self-regulated, they can think more clearly. For example, practice taking a breath with children as a self-regulation technique during calm moments. Then, when challenges arise, children have a strategy they have practiced many times and can use to calm down before problem-solving begins.  
• Encourage children's efforts to voice the problem and their feelings after they are calm. For example, when a challenge arises, encourage children to use the phrase, "The problem is_______, and I feel______." This process sets the stage to begin problem-solving.
• Acknowledge children's efforts to think about varied ways to solve problems. For example, an educator says, "It looks like you and Nila are trying to work out how to share the blocks. What do you think might work so you can both play with them? Do you have some other ideas about how you could share?"
• Champion children's efforts as they problem-solve. For example, "You and Nila thought about two ways you could share. One way is to divide the red blocks so you can each build, and the other is to build a tower together. Great thinking, friends!"
• Create opportunities for activities and play that offer problem-solving practice. For example, when children play together in the block area, it provides opportunities to negotiate plans for play and role-play, build perspective, talk about feelings, and share. The skills children learn during play, along with adult support, enhance children’s ability to solve more complex and challenging social problems and conflicts when they occur in and out of the early learning setting.

References: 

Paley, B., & Hajal, N. J. (2022). Conceptualizing emotion regulation and coregulation as family-level phenomena. Clinical Child and Family Psychology Review ,  25 (1), 19-43.

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