RotateMatrix.java

public class RotateMatrix {
    
    public void rotate(int[][] matrix) {
        int l = 0;
        int r = matrix.length - 1;
        
        while ( l < r ) {
            for(int i = 0; i < r - l; i++) {
                int top = l;
                int bottom = r;
                 //save the topleft
                int topLeft = matrix[top][l + i];

                //move bottom left into top left
                matrix[top][l + i] = matrix[bottom - i][l];

                // move bottom right into bottom left
                matrix[bottom - i][l] = matrix[bottom][r - i];

                // move top right into bottom right
                matrix[bottom][r - i] = matrix[top + i][r];

                // move top left into top right
                matrix[top + i][r] = topLeft;
                
            }
            
            r -= 1;
            l += 1;
        }
    }
}