Java基本类型与byte数组的转换

Java基本类型与byte数组之间相互转换：

package cn.teaey.utils;

import java.nio.charset.Charset;

public class ByteUtil
{
public static byte[] getBytes(short data)
{
byte[] bytes = new byte[2];
bytes[0] = (byte) (data & 0xff);
bytes1 = (byte) ((data & 0xff00) >> 8);
return bytes;
}

public static byte[] getBytes(char data)
{
    byte[] bytes = new byte[2];
    bytes[0] = (byte) (data);
    bytes[1] = (byte) (data >> 8);
    return bytes;
}

public static byte[] getBytes(int data)
{
    byte[] bytes = new byte[4];
    bytes[0] = (byte) (data & 0xff);
    bytes[1] = (byte) ((data & 0xff00) >> 8);
    bytes[2] = (byte) ((data & 0xff0000) >> 16);
    bytes[3] = (byte) ((data & 0xff000000) >> 24);
    return bytes;
}

public static byte[] getBytes(long data)
{
    byte[] bytes = new byte[8];
    bytes[0] = (byte) (data & 0xff);
    bytes[1] = (byte) ((data >> 8) & 0xff);
    bytes[2] = (byte) ((data >> 16) & 0xff);
    bytes[3] = (byte) ((data >> 24) & 0xff);
    bytes[4] = (byte) ((data >> 32) & 0xff);
    bytes[5] = (byte) ((data >> 40) & 0xff);
    bytes[6] = (byte) ((data >> 48) & 0xff);
    bytes[7] = (byte) ((data >> 56) & 0xff);
    return bytes;
}

public static byte[] getBytes(float data)
{
    int intBits = Float.floatToIntBits(data);
    return getBytes(intBits);
}

public static byte[] getBytes(double data)
{
    long intBits = Double.doubleToLongBits(data);
    return getBytes(intBits);
}

public static byte[] getBytes(String data, String charsetName)
{
    Charset charset = Charset.forName(charsetName);
    return data.getBytes(charset);
}

public static byte[] getBytes(String data)
{
    return getBytes(data, "GBK");
}

public static short getShort(byte[] bytes)
{
    return (short) ((0xff & bytes[0]) | (0xff00 & (bytes[1] << 8)));
}

public static char getChar(byte[] bytes)
{
    return (char) ((0xff & bytes[0]) | (0xff00 & (bytes[1] << 8)));
}

public static int getInt(byte[] bytes)
{
    return (0xff & bytes[0]) | (0xff00 & (bytes[1] << 8)) | (0xff0000 & (bytes[2] << 16)) | (0xff000000 & (bytes[3] << 24));
}

public static long getLong(byte[] bytes)
{
    return(0xffL & (long)bytes[0]) | (0xff00L & ((long)bytes[1] << 8)) | (0xff0000L & ((long)bytes[2] << 16)) | (0xff000000L & ((long)bytes[3] << 24))
     | (0xff00000000L & ((long)bytes[4] << 32)) | (0xff0000000000L & ((long)bytes[5] << 40)) | (0xff000000000000L & ((long)bytes[6] << 48)) | (0xff00000000000000L & ((long)bytes[7] << 56));
}

public static float getFloat(byte[] bytes)
{
    return Float.intBitsToFloat(getInt(bytes));
}

public static double getDouble(byte[] bytes)
{
    long l = getLong(bytes);
    System.out.println(l);
    return Double.longBitsToDouble(l);
}

public static String getString(byte[] bytes, String charsetName)
{
    return new String(bytes, Charset.forName(charsetName));
}

public static String getString(byte[] bytes)
{
    return getString(bytes, "GBK");
}

public static void main(String[] args)
{
    short s = 122;
    int i = 122;
    long l = 1222222;

    char c = 'a';

    float f = 122.22f;
    double d = 122.22;

    String string = "我是好孩子";
    System.out.println(s);
    System.out.println(i);
    System.out.println(l);
    System.out.println(c);
    System.out.println(f);
    System.out.println(d);
    System.out.println(string);

    System.out.println("**************");

    System.out.println(getShort(getBytes(s)));
    System.out.println(getInt(getBytes(i)));
    System.out.println(getLong(getBytes(l)));
    System.out.println(getChar(getBytes(c)));
    System.out.println(getFloat(getBytes(f)));
    System.out.println(getDouble(getBytes(d)));
    System.out.println(getString(getBytes(string)));
}

}

java的基本类型存储长度都是固定的，不因机器的不同而不同，因此使java拥有了良好的移植性。

最近在做项目时，需要在一个变量里存放16位长的二进制数字，查看上表可知short类型正好符合需要。

但是因为java中的数字类型都是有符号的，因此short类型的第一位被用于表示符号，实际存储长度只有15位，

即－7FFF－＋7FFF。那如果要存放＋7FFF－＋FFFF的数字该怎么办呢？只有采取变通的办法，采用变换算法。我们可以利用－7FFF－－0001来存放大于7FFF的数字。转换公式为－(FFFF－X)－1。由于有了符号，所以＋0000和－0000是相等的，所以比无符号数少了1个数字，所以要在公式里减1，由于这个问题，用这个方法我们就不能存放＋8000了。

用这个方法可以基本满足我们的需要，如有特殊需要，如要存储＋8000，那只有采取别的办法了。