Java byte到Int的转换
Java byte到Int的转换有两种:

1. 带符号转换,数值转换
2. 无符号转换

byte本身是带正负符号的, 默认向上转换也是带符号

带符号转换

byte本身是带正负符号的, 默认向上转换也是带符号

方法1 默认转换

		byte b = -3;
		int i = b;
		System.out.println(i); // 结果是 -3

方法2 强制转换

		byte b = -3;
		int i = (int)b;
		System.out.println(i); // 结果是 -3

无符号转换

方法1 i = Byte.toUnsignedInt(b);

i = Byte.toUnsignedInt(b);

源码是?

    /**
     * Converts the argument to an {@code int} by an unsigned
     * conversion.  In an unsigned conversion to an {@code int}, the
     * high-order 24 bits of the {@code int} are zero and the
     * low-order 8 bits are equal to the bits of the {@code byte} argument.
     *
     * Consequently, zero and positive {@code byte} values are mapped
     * to a numerically equal {@code int} value and negative {@code
     * byte} values are mapped to an {@code int} value equal to the
     * input plus 2<sup>8</sup>.
     *
     * @param  x the value to convert to an unsigned {@code int}
     * @return the argument converted to {@code int} by an unsigned
     *         conversion
     * @since 1.8
     */
    public static int toUnsignedInt(byte x) {
        return ((int) x) & 0xff;
    }

1.8版才有? ?

方法2 i = b&0xff;

i = b&0xff;
或者
i = b&0xFF;

方法3 i = b&255;

i = b&255;

方法4 if(b<0)i=b+256; else i=b;

if(b<0)i=b+256; else i=b;

方法5 i = b<0 ? b+256 : b;

i = b<0 ? b+256 : b;

测试代码1

public class T2206040611 {

	public static void main(String[] args) {
		byte b = -3;
		int i;
		i = b;		System.out.println(i);
		i = (int)b;		System.out.println(i);
		i = Byte.toUnsignedInt(b);		System.out.println(i);
		i = b&0xff;		System.out.println(i);
		i = b&255;		System.out.println(i);
		if(b<0)i=b+256; else i=b; System.out.println(i);
		i = b<0 ? b+256 : b; System.out.println(i);
	}

}

结果

-3
-3
253
253
253
253
253