Rotate matrix clockwise, Java

Rotate matrix clockwise

//'main' method must be in a class 'Rextester'.
//Compiler version 1.8.0_111

import java.util.*;
import java.lang.*;

//Rotate nXn 2D matrix by 90degrees

class Rextester
{  
    public static void main(String args[])
    {
        System.out.println("Hello, World!");
        
    }
    public static void rotate(int[][] matrix) {
        //1. Rows become columns
        //2. First column becomes last column & so on.
            
        //[]i,j] to [j,i]
        for(int i = 0;i<matrix.length;i++){
            for(int j =i;j<matrix[0].length;j++){
                int tmp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = tmp;
            }
        }

int n = matrix.length;
        //up is down
        for(int i = 0;i<matrix.length;i++){
            for(int j = 0;j<matrix[0].length/2;j++){
                int tmp = matrix[i][n-j-1];
                matrix[i][n-j-1] = matrix[i][j];
                matrix[i][j] = tmp;
            }
        }

}


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