java中int與byte，以及long與byte之間的轉換

原文地址：

http://blog.csdn.net/zgyulongfei/article/details/7738970

public class Utilities {
    
    public static byte[] int2Bytes(int num) {
        byte[] byteNum = new byte[4];
        for (int ix = 0; ix < 4; ++ix) {
            int offset = 32 - (ix + 1) * 8;
            byteNum[ix] = (byte) ((num >> offset) & 0xff);
        }
        return byteNum;
    }

    public static int bytes2Int(byte[] byteNum) {
        int num = 0;
        for (int ix = 0; ix < 4; ++ix) {
            num <<= 8;
            num |= (byteNum[ix] & 0xff);
        }
        return num;
    }

    public static byte int2OneByte(int num) {
        return (byte) (num & 0x000000ff);
    }

    public static int oneByte2Int(byte byteNum) {
        return byteNum > 0 ? byteNum : (128 + (128 + byteNum));
    }

    public static byte[] long2Bytes(long num) {
        byte[] byteNum = new byte[8];
        for (int ix = 0; ix < 8; ++ix) {
            int offset = 64 - (ix + 1) * 8;
            byteNum[ix] = (byte) ((num >> offset) & 0xff);
        }
        return byteNum;
    }

    public static long bytes2Long(byte[] byteNum) {
        long num = 0;
        for (int ix = 0; ix < 8; ++ix) {
            num <<= 8;
            num |= (byteNum[ix] & 0xff);
        }
        return num;
    }

    public static void main(String[] args) {
        int num = 129;
        System.out.println("測試的int值為:" + num);

        byte[] int2bytes = Utilities.int2Bytes(num);
        System.out.printf("int轉成bytes: ");
        for (int i = 0; i < 4; ++i) {
            System.out.print(int2bytes[i] + " ");
        }
        System.out.println();

        int bytes2int = Utilities.bytes2Int(int2bytes);
        System.out.println("bytes轉行成int: " + bytes2int);

        byte int2OneByte = Utilities.int2OneByte(num);
        System.out.println("int轉行成one byte: " + int2OneByte);

        int oneByte2Int = Utilities.oneByte2Int(int2OneByte);
        System.out.println("one byte轉行成int: " + oneByte2Int);
        System.out.println();

        long longNum = 100000;
        System.out.println("測試的long值為：" + longNum);

        byte[] long2Bytes = Utilities.long2Bytes(longNum);
        System.out.printf("long轉行成bytes: ");
        for (int ix = 0; ix < long2Bytes.length; ++ix) {
            System.out.print(long2Bytes[ix] + " ");
        }
        System.out.println();

        long bytes2Long = Utilities.bytes2Long(long2Bytes);
        System.out.println("bytes轉行成long: " + bytes2Long);
    }
}

測試的int值為:129
int轉成bytes: 0 0 0 -127
bytes轉行成int: 129
int轉行成one byte: -127
one byte轉行成int: 129

測試的long值為：100000
long轉行成bytes: 0 0 0 0 0 1 -122 -96
bytes轉行成long: 100000