java中的移位运算符

<<  左移 ：按二进制形式把所有的数字向左移动对应的位数，高位移出（舍弃），低位的空位补零。

>> 带符号右移　：按二进制形式把所有的数字向右移动对应位数，低位移出（舍弃），高位的空位补符号位，即正数补零，负数补1.

>>> 无符号右移　：按二进制形式把所有的数字向右移动对应位数，低位移出（舍弃），高位的空位补零。对于正数来说和带符号右移相同，对于负数来说不同。

　　　　int i = 12;
		System.out.println("i = " + i + " and binary is " + Integer.toBinaryString(i));
		System.out.println("i << 2 = " + Integer.toBinaryString(i<<2));
		System.out.println("i >> 2 = " + Integer.toBinaryString(i>>2));
		System.out.println("i >>> 2 = " + Integer.toBinaryString(i>>>2));
		
		System.out.println("==========================================================================");
		
		int j = -1;
		System.out.println("j = " + j  + " and binary is " + Integer.toBinaryString(j));
		System.out.println("j << 2 = " + Integer.toBinaryString(j<<2));
		System.out.println("j >> 2 = " + Integer.toBinaryString(j>>2)); //?
		System.out.println("j >>> 2 = " + Integer.toBinaryString(j>>>2)); 

打印出结果是：

i = 12 and binary is 1100
i << 2 = 110000
i >> 2 = 11
i >>> 2 = 11
==========================================================================
j = -1 and binary is 11111111111111111111111111111111
j << 2 = 11111111111111111111111111111100
j >> 2 = 11111111111111111111111111111111  --不明白
j >>> 2 = 111111111111111111111111111111