对一个数异或两次等于没有异或

public class xortest {
	public static void main(String[] args) {
		int a = 10;
		int b = 20;
		System.out.println(a ^ b);
		System.out.println(a ^ b ^ a);
		System.out.println(a ^ b ^ b);
		System.out.println(a ^ a);
	}

}

30
20
10
0