JRE

JRE (Java Runtime Environment)

Definition

JRE is the space where a Java program runs (gets executed). It provides the environment necessary to run Java applications.

What does JRE contain?

• JVM (Java Virtual Machine) – The engine that runs Java bytecode
• Libraries and Class Files – Predefined Java libraries required to run programs
• Other Supporting Files – Configuration and runtime tools

Purpose

• JRE does not compile code — it only runs already compiled Java programs (.class files).
• It ensures your program runs consistently on any system that has JRE installed.

Summary

JRE is like a stage where your Java play (program) is performed.
It doesn’t write the play — it just performs it.

Flow

public class Program {
    public static void main(String[] args) {
        add();
    }
    static void add(){
        int a = 10;
        int b = 20;
        int c = a+b;
        System.out.println(c);
    }
}

What Happens When a Method is Called?

Whenever a method is called in Java:

• A stack frame (also called an activation record) is created in the stack segment of memory.
• This stack frame holds all the information required for the method's execution.
• When the method execution is completed, its stack frame is removed (popped) from the stack.

Stack Frame (Activation Record)

• A stack frame is a block of memory that is allocated on the stack segment.
• It stores:
  • Local variables
  • Return address
  • Parameters
  • Temporary data used during method execution

Local Variables

• Local variables are the variables declared inside a method.
• Their memory is allocated within the method's stack frame.
• These variables are accessible only during the method's execution and are destroyed once the method ends.

import java.util.Scanner;

public class RemainderCalculator {

    // Method to calculate remainder
    public static double findRemainder(double num1, double num2) {
        return num1 % num2;
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        // Input two double numbers
        System.out.print("Enter first number: ");
        double a = sc.nextDouble();

        System.out.print("Enter second number: ");
        double b = sc.nextDouble();

        // Call the method to find remainder
        double result = findRemainder(a, b);

        // Output the result
        System.out.println("Remainder: " + result);

        sc.close();
    }
}