Integer reverse() Method In Java

Last Updated : 07 Jul, 2018

The java.lang.Integer.reverse() is an inbuilt method in Java and is used to return the reverse order of the bits in the two's complement binary representation of the specified int value. Syntax:

public static int reverse(int a)

Parameters: The parameter a is an integer value whose bits are to be reversed. Return Value: The method returns the value which is obtained by reversing the order of the bits in the specified int value. Examples:

Input: 86
Output: 1778384896
Explanation:
Consider an integer a = 86
Binary Representation = 1010110
The number of one bit = 4 
After reversing it is = 1778384896

Input: 168
Output: 352321536

Below programs illustrate the java.lang.Integer.reverse() method: Program 1: For a positive number.

// Java program to illustrate the
// Java.lang.Integer.reverse() method
import java.lang.*;

public class geeks {

    public static void main(String[] args)
    {

        int a = 168;
        System.out.println("Number = " + a);

        // It returns the value obtained by reversing order of the bits
        System.out.println("By reversing we get = " + Integer.reverse(a));
    }
}

 
// Java program to illustrate the
// Java.lang.Integer.reverse() method
import java.lang.*;
​
public class geeks {
​
    public static void main(String[] args)
    {
​
        int a = 168;
        System.out.println("Number = " + a);
​
        // It returns the value obtained by reversing order of the bits
        System.out.println("By reversing we get = " + Integer.reverse(a));
    }
}

Output:

Number = 168
By reversing we get = 352321536

Program 2: For a Negative number.

// Java program to illustrate the
// Java.lang.Integer.reverse() method
import java.lang.*;

public class geeks {

    public static void main(String[] args)
    {

        int a = -72;
        System.out.println("Number = " + a);

        // It returns the value obtained by reversing order of the bits
        System.out.println("By reversing we get = " + Integer.reverse(a));
    }
}

 
// Java program to illustrate the
// Java.lang.Integer.reverse() method
import java.lang.*;
​
public class geeks {
​
    public static void main(String[] args)
    {
​
        int a = -72;
        System.out.println("Number = " + a);
​
        // It returns the value obtained by reversing order of the bits
        System.out.println("By reversing we get = " + Integer.reverse(a));
    }
}

Output:

Number = -72
By reversing we get = 503316479

Program 3: For a decimal value and string. Note: It throws an error message when a decimal value or string is passed as an argument.

// Java program to illustrate the
// Java.lang.Integer.reverse() method
import java.lang.*;

public class geeks {

    public static void main(String[] args)
    {

        int a = 37.9;
        System.out.println("Number = " + a);

        // It returns the value obtained by reversing order of the bits in
        // the specified int value
        System.out.println("By reversing we get = " + Integer.reverse(a));
        a = "21";
        System.out.println("Number = " + a);

        // It returns the value obtained by reversing order of the bits in
        // the specified int value
        System.out.println("By reversing we get = " + Integer.reverse(a));
    }
}

 
// Java program to illustrate the
// Java.lang.Integer.reverse() method
import java.lang.*;
​
public class geeks {
​
    public static void main(String[] args)
    {
​
        int a = 37.9;
        System.out.println("Number = " + a);
​
        // It returns the value obtained by reversing order of the bits in
        // the specified int value
        System.out.println("By reversing we get = " + Integer.reverse(a));
        a = "21";
        System.out.println("Number = " + a);
​
        // It returns the value obtained by reversing order of the bits in
        // the specified int value
        System.out.println("By reversing we get = " + Integer.reverse(a));
    }
}

Output:

prog.java:9: error: incompatible types: possible lossy conversion from double to int
    int a = 37.9;
            ^
prog.java:17: error: incompatible types: String cannot be converted to int
     a = "21";
         ^
2 errors