Java 中 byte、byte 数组和 int、long 之间的转换

public class Test {

private static ByteBuffer buffer = ByteBuffer.allocate(8);

public static void main(String[] args) {

//测试 int 转 byte
int int0 = 234;
byte byte0 = intToByte(int0);
System.out.println("byte0=" + byte0);//byte0=-22
//测试 byte 转 int
int int1 = byteToInt(byte0);
System.out.println("int1=" + int1);//int1=234

//测试 int 转 byte 数组
int int2 = 1417;
byte[] bytesInt = intToByteArray(int2);
System.out.println("bytesInt=" + bytesInt);//bytesInt=[B@de6ced
//测试 byte 数组转 int
int int3 = byteArrayToInt(bytesInt);
System.out.println("int3=" + int3);//int3=1417

//测试 long 转 byte 数组
long long1 = 2223;
byte[] bytesLong = longToBytes(long1);
System.out.println("bytes=" + bytesLong);//bytes=[B@c17164
//测试 byte 数组 转 long
long long2 = bytesToLong(bytesLong);
System.out.println("long2=" + long2);//long2=2223
}

//byte 与 int 的相互转换
public static byte intToByte(int x) {
return (byte) x;
}

public static int byteToInt(byte b) {
//Java 总是把 byte 当做有符处理；我们可以通过将其和 0xFF 进行二进制与得到它的无符值
return b & 0xFF;
}

//byte 数组与 int 的相互转换
public static int byteArrayToInt(byte[] b) {
return   b[3] & 0xFF |
(b[2] & 0xFF) << 8 |
(b[1] & 0xFF) << 16 |
(b[0] & 0xFF) << 24;
}

public static byte[] intToByteArray(int a) {
return new byte[] {
(byte) ((a >> 24) & 0xFF),
(byte) ((a >> 16) & 0xFF),
(byte) ((a >> 8) & 0xFF),
(byte) (a & 0xFF)
};
}

//byte 数组与 long 的相互转换
public static byte[] longToBytes(long x) {
buffer.putLong(0, x);
return buffer.array();
}

public static long bytesToLong(byte[] bytes) {
buffer.put(bytes, 0, bytes.length);
buffer.flip();//need flip
return buffer.getLong();
}

}