Difference Between Stack and Heap Memory in Java

JVM has divided memory space between two parts: one is Stack and another one is Heap space. Stack space is mainly used for storing order of method execution and local variables.

Stacks always store blocks in LIFO order whereas heap memory uses dynamic allocation for allocating and deallocating memory blocks. 

Memory allocated to the heap lives until one of the following events occurs :

• Program terminated 
• Memory free 

What is a Heap memory?

Heap memory is allocated for storing objects, arrays, and JRE (Java Runtime Environment) classes. Memory may be allocated at random address and automatically free memory that is not in use.

Example

The following is an example of a heap in Java:

public class HeapExample {
    public static void main(String[] args) {
        int[] numbers = new int[3];  // Array object in heap
        numbers[0] = 5;
        numbers[1] = 10;
        numbers[2] = 15;

        for (int num : numbers) {
            System.out.println(num);
        }
    }
}

The output of the above Java program is:

5
10
15

What is a Stack memory?

Stack memory is used to store items that have a very short life, such as local variables and reference variables of objects. It follows the LIFO (Last-In First-Out) principle and is automatically managed during method calls and exits.

Example

The following is an example of stack in java:

public class StackExample {
    public static void main(String[] args) {
        int a = 10;   // stored in stack
        int b = 20;   // stored in stack
        int sum = add(a, b);  // method call adds a new frame on the stack
        System.out.println("Sum: " + sum);
    }

    public static int add(int x, int y) {
        int result = x + y;  // local variable in stack
        return result;
    }
}

The output of the above Java program is:

Sum: 30

Difference Between Stack and Heap Memory

Below are the differences between Stack and Heap Memory: