java常用位操作

版权声明：自由转载，无需过问 https://blog.csdn.net/Next__One/article/details/78767284

public class TestIndex {
    /**
     * 数组越界
     * 这个方法是java源码中常用的一个数组越界的判断检测
     * 顺便复习一下位操作
     */
    public static int read(byte[] b, int off, int len) throws Exception {
        // parameter check
        int result = off | len | (off + len) |(b.length - (off+len));
        if (result < 0) {
            System.out.println(result);
        } else if (len == 0) {
            return 0;
        }
        return result;
    }

    /**
     * 将一个高位在前的字节数组转为int
     * @param num
     * @return
     */
    public static byte[] intToBytes(int num){
        byte[] bytes = new byte[4];
        bytes[0] = (byte) (num >>> 24);
        bytes[1] = (byte) (num >>> 16);
        bytes[2] = (byte) (num >>> 8);
        bytes[3] = (byte) (num >>> 0);
        return bytes;
    }

    /**
     * 将一个高位在前的字节数组转为int
     * @param bytes
     * @return
     */
    public static int byteToInt(byte[] bytes){
        int _1 = bytes[0] << 24;
        int _2 = bytes[1] << 16;
        int _3 = bytes[2] << 8;
        int _4 = bytes[3] << 0;
        return _1 | _2 | _3 | _4;
    }

    /**
     * 显示一个byte数组
     * @param bytes
     */
    public static void showByte(byte[] bytes){
        for (byte b : bytes) {
            System.out.print(byteToBit(b) +" ");
        }
        System.out.println();
    }

    /** 
     * 将byte转换为一个长度为8的byte数组，数组每个值代表bit 
     */  
    public static byte[] getBooleanArray(byte b) {  
        byte[] array = new byte[8];  
        for (int i = 7; i >= 0; i--) {  
            array[i] = (byte)(b & 1);  
            b = (byte) (b >> 1);  
        }  
        return array;  
    }  
    /** 
     * 把byte转为字符串的bit 
     */  
    public static String byteToBit(byte b) {  
        return ""  
                + (byte) ((b >> 7) & 0x1) + (byte) ((b >> 6) & 0x1)  
                + (byte) ((b >> 5) & 0x1) + (byte) ((b >> 4) & 0x1)  
                + (byte) ((b >> 3) & 0x1) + (byte) ((b >> 2) & 0x1)  
                + (byte) ((b >> 1) & 0x1) + (byte) ((b >> 0) & 0x1);  
    }  

    public static void main(String[] args) {
        int num = 100;
        byte[] bytes = intToBytes(num);
        showByte(bytes);
        num = byteToInt(bytes);
        System.out.println(num);
    }
}