Question

Swapping the values of two variables involves the exchange of their values. For example, assume that a == 5; and b == 10; If the values of these variables were swapped, the resultant values would be: a == 10; b == 5.

Write a program to initialise two memory locations with values 10 and 5 before then swapping them without the use of a third memory location using:

1. The IJVM instruction set.
2. Create a table with the values of all relevant memory locations and registers at each step

Answer 1

// Java program to swap two numbers without using third memory location

import java.*;

class Swap {   

    public static void main(String a[])

    {

        int a = 10;

        int b = 5;

a = a + b;

b = a - b;

a = a - b;

    }

}

Local Variable indices: a = 10, b = 5.

Java	IJVM Assembly	IJVM ISA
	ILOAD a	0X15 0X02
{	ILOAD b	0X15 0X03
a = a + b;	IADD	0X60
	ISTORE a	0X36 0X02
	ILOAD a	0X15 0X02
	ILOAD b	0X15 0X03
b = a - b;	ISUB	0X64
	ISTORE b	0X36 0X03
	ILOAD a	0X15 0X02
	ILOAD b	0X15 0X03
a = a - b;	ISUB	0X64
}	ISTORE a	0X36 0X02

Output : a = 5, b = 10.