What is Thread in Java : How They Work and Why You Need Them

What is Thread in Java, it’s useful to first have a basic understanding of the segments of memory in RAM that a program uses. Typically, a program’s memory is divided into four segments:

Code Segment :

• This part of memory contains the executable instructions of a program.
• It is usually read-only to prevent accidental modification of instructions.
• All threads of a process share this segment.

Stack Segment:

• The stack segment is used stores local variables, Methods parameters, return addresses, and the call stack.

Each thread in a process has its own stack segment to maintain its own function call history and local variables.

class Class2 {
    public void method1() {
        // Print numbers from 1 to 20 with a delay of 3 seconds between each number
        for (int i = 1; i <= 20; i++) {
            System.out.print(i + " ");
            try {
                Thread.sleep(300); // Delay for 3000 milliseconds (3 seconds)
            } catch (InterruptedException e) {
                
            }
        }
        System.out.println(); // Print a new line after printing numbers
    }

    public void method2() {
        // Print numbers from 21 to 40 with a delay of 3 seconds between each number
        for (int i = 21; i <= 40; i++) {
            System.out.print(i + " ");
            try {
                Thread.sleep(300); // Delay for 3000 milliseconds (3 seconds)
            } catch (InterruptedException e) {
                
            }
        }
       
        System.out.println(); // Print a new line after printing number
    }
}

public class Class1 {
    public static void main(String[] args) {
        Class2 obj = new Class2();
        
        // Call method1 from Class2
        
        obj.method1();
        obj.method2();
    }
}

The provided program defines 2 classes, Class1 and Class2, and it shows a simple use case where methods from Class2 are invoked sequentially to print numbers with a delay. Here is a detailed explanation of the program:

Class2

Class2 contains two methods, method1 and method2, each responsible for printing a sequence of numbers with a delay in milliscounds.

method1():

• This method prints numbers from 1 to 20.
• Each number is followed by a space.
• After printing each number, the method pauses for 300 milliseconds (not 3 seconds, as mentioned in the comments; 300 milliseconds is 0.3 seconds).
• The delay is implemented using Thread.sleep(300).
• If an InterruptedException occurs during the sleep, it is caught and ignored.
• After printing the sequence, a newline character is printed to move to the next line.

method2():

• This method prints numbers from 21 to 40.
• The behavior is similar to method1(), including the delay and exception handling.
• After printing the sequence, a newline character is printed.

Class1

Class1 contains the main method, which is the entry point of the program.

main():

• An instance of Class2 is created (obj).
• method1 of the Class2 instance (obj) is called, which prints numbers from 1 to 20.
• After method1 completes, method2 of the Class2 instance (obj) is called, which prints numbers from 21 to 40.

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Execution Flow

Creating an Instance of Class2:

• Class2 obj = new Class2();
• An object obj of Class2 is created.

Calling method1():

• obj.method1();
• This prints numbers from 1 to 20 with a delay of 300 milliseconds between each number.

Calling method2():

• obj.method2();
• This prints numbers from 21 to 40 with a delay of 300 milliseconds between each number.

Example Output

The program will produce the following output with a delay of 300 milliseconds between each number:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 
21 22 23 24 25 26 27 28 29 30 3 32 33 34 35 36 37 38 39 40

• Stack grows & shrinks as functions are called and return.

Heap Segment:

• The heap is used for dynamic memory allocation. This means that memory can be allocated, deallocated at runtime using functions.
• The heap is shared among all threads within a process.
• It is typically larger and more flexible than the stack but requires manual management.

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FAQs: Thread in Java