[CC150][1.5] Given an image represented by an NxN matrix, where each pixel in the image is 4 bytes, write a method to rotate the image by 90 degrees. Can you do this in place?

Image.java

public class Image {
	private int N;
	private int[][] img;
	public Image(int[][] image) {
		if (image == null) throw new NullPointerException();
		this.img = image;
		if (image.length != image[0].length) throw new IllegalArgumentException();
		this.N = image[0].length;
	}
	
	//*	need total [(N-1) + (N-3) + ...3 + 1]*3 exchange if N is even
	// 	need total [(N-1) + (N-3) + ...4 + 2 + 0]*3 exchange if N is odd
	//* time O(N^2)
	public void rotate(String s) {
		if (s == "ClockWise") {
			for (int j = N - 1; j > (N - 1)/2; j--) { 
				for (int i = (N - 1) - j; i < j; i++ ) { 
					exch(i, j, j, N - 1 - i); //(dstX, dstY) =  (j, N - 1 - i)
					exch(i, j, N - 1 - i, N - 1 - j); // (dstX, dstY) = (odl_dstY, N-1-old_dstX)
					exch(i, j, N - 1 - j, i); // (dstX, dstY) = (odl_dstY, N-1-old_dstX)
				}
			}
		}
		else if (s == "CounterClockWise") {
			for (int j = N - 1; j > (N - 1)/2; j--) {
				for (int i = (N - 1) - j; i < j; i++ ) {
					exch(i, j, N - 1 - j, i);
					exch(i, j, N - 1 - i, N - 1 - j);
					exch(i, j, j, N - 1 -i);
				}
			}
		}	
		else throw new UnsupportedOperationException("Invalid operation");
	}
	
	public String toString() {
		String s = "";
		for (int i = 0; i < N; i++) {
			for (int j = 0; j < N; j++)
				s += img[i][j] + " ";
			s += "\n";
		}
		return s;
	}
	
	//* Helpler function, in-place exchane
	private void exch(int srcX, int srcY, int dstX, int dstY) {
		img[srcX][srcY] ^= img[dstX][dstY];
		img[dstX][dstY] ^= img[srcX][srcY];
		img[srcX][srcY] ^= img[dstX][dstY];		
	}
	
	public static void main(String[] args) {
		System.out.println("***********TEST**************");
		int[][] testA = {{1}};
		Image a = new Image(testA);
		System.out.print(a.toString());
		
		a.rotate("ClockWise");
		System.out.println("\nClockWise:");
		System.out.print(a.toString());;
		
		a.rotate("CounterClockWise");
		System.out.println("\nCounterClockWise:");
		System.out.print(a.toString());;
		
		System.out.println("***********TEST**************");
		int[][] testB = {{1,2},{3,4}};
		Image b = new Image(testB);
		System.out.print(b.toString());
		
		b.rotate("ClockWise");
		System.out.println("\nClockWise:");
		System.out.print(b.toString());
		
		b.rotate("CounterClockWise");
		System.out.println("\nCounterClockWise:");
		System.out.print(b.toString());;
		
		System.out.println("***********TEST**************");
		int[][] testC = {{1,2,3},{4,5,6},{7,8,9}};
		Image c = new Image(testC);
		System.out.print(c.toString());
		
		c.rotate("ClockWise");
		System.out.println("\nClockWise:");
		System.out.print(c.toString());
		
		c.rotate("CounterClockWise");
		System.out.println("\nCounterClockWise:");
		System.out.print(c.toString());;
		
		System.out.println("***********TEST**************");
		int[][] testD = {{1,2,3,4},{5,6,7,8},{9,10,11,12},{13,14,15,16}};
		Image d = new Image(testD);
		System.out.print(d.toString());
		
		d.rotate("ClockWise");
		System.out.println("\nClockWise:");
		System.out.print(d.toString());
		
		d.rotate("CounterClockWise");
		System.out.println("\nCounterClockWise:");
		System.out.print(d.toString());;
		
		System.out.println("***********TEST**************");
		int[][] testE = {{1,2,3,4,5},{6,7,8,9,10},{11,12,13,14,15},{16,17,18,19,20},
				{21,22,23,24,25}};
		Image e = new Image(testE);
		System.out.print(e.toString());
		
		e.rotate("ClockWise");
		System.out.println("\nClockWise:");
		System.out.print(e.toString());
		
		e.rotate("CounterClockWise");
		System.out.println("\nCounterClockWise:");
		System.out.print(e.toString());;
		
	}
}