int byte transfer relationship with the complement of

Source: http: //blog.sina.com.cn/s/blog_6cbe0cff0101ekfl.html 

public class Test {
    public static void main(String[] args) {
        int start = -131;
        int end = 131;

        for (int i = start; i < end; i++)
            if ((byte) i != i)
                System.out.println("原数：" + i + "\t转化后:" + (byte) i);
    }

}

Original number: after -131 Conversion: 125 
Number of Original: after -130 Conversion: 126 
Number of Original: after -129 Conversion: 127 
original number: 128 after conversion: -128 
Number Original: 129 after conversion: -127 
original number: 130 Conversion after: -126

 

 Why does this happen?

    Since the Java byte that represents only between -128 and 127 store 8 bits, when forced into the int type byte, the system taken after 8 taken int practice.

// store Java's complement integer, int type is a 32-bit, byte 8-bit   
@ 130 then representation in memory: 00000000 00000000 00000000 10000010   
@ 8 taken after this becomes 10000010, the complement representation the first time is the sign bit, 0 positive 1 negative,   
// so you can know that is certainly a negative number 10000010, and then look at its value part,   
// complement the positive becomes negative, positive or negative change, methods: "bitwise, plus 1",   
// so it should become 1111101 0000010 + 1 = 1111110 (ie 126)   
// and because it is negative, so the interception becomes -126   

// we look at -130 examples of (sign bit is 1, the remaining bitwise + 1)   
// --130 representation in memory: 1,111,111,111,111,111 1,111,111,101,111,110   
// so taken after 8 becomes 01111110   
// this is obviously an integer ah, then numerical part 126   
// 64 + 32 + 16 + 8 + 4 + 2 = 126