byte数组和int互转

import java.nio.ByteBuffer;



public class Program

{

    public static void main(String[] args)

    {

        ByteBuffer buf = ByteBuffer.allocate(3);



        writeInt24(-113, buf);

        buf.flip();

        int i1 = readInt24(buf);



        buf.clear();

        writeInt24(9408399, buf);

        buf.flip();

        int i2 = readUnsigedInt24(buf);//readInt24(buf);



        System.out.println("i1 = " + i1);

        System.out.println("i2 = " + i2);

    }



    static void writeInt24(int val, ByteBuffer buf)

    {

        buf.put((byte)(val >> 16));

        buf.put((byte)(val >> 8));

        buf.put((byte)val);

    }



    static int readInt24(ByteBuffer buf)

    {

        byte[] data = new byte[3];

        for (int i = 0; i < 3; ++i)

            data[i] = buf.get();



        return (data[0] << 16)

                | (data[1] << 8 & 0xFF00)

                | (data[2] & 0xFF);// Java总是把byte当做有符号处理；我们可以通过将其和0xFF进行二进制与来得到有符号的整型

    }



    static int readUnsigedInt24(ByteBuffer buf)

    {

        byte[] data = new byte[3];

        for (int i = 0; i < 3; ++i)

            data[i] = buf.get();



        return (data[0] << 16 & 0xFF0000)

                | (data[1] << 8 & 0xFF00)

                | (data[0] & 0xFF);

    }

}