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標題: java中byte數組與int，long，short，float，char之間的轉換 [打印本頁]

作者: wf18332700757 時間: 2018-6-21 23:04
標題: java中byte數組與int，long，short，float，char之間的轉換
Byte和int之間的轉換
/**
  *將32位的int值放到4字節的里
  * @param num
  * @return
  */
public static byte[] int2byteArray(int num) {
byte[] result = new byte[4];
result[0] = (byte)(num >>> 24);//取最高8位放到0下標
result[1] = (byte)(num >>> 16);//取次高8為放到1下標
result[2] = (byte)(num >>> 8); //取次低8位放到2下標
result[3] = (byte)(num );    //取最低8位放到3下標
return result;
}

/**
  * 將4字節的byte數組轉成一個int值
  * @param b
  * @return
  */
public static int byteArray2int(byte[] b){
byte[] a = new byte[4];
int i = a.length - 1,j = b.length - 1;
for (; i >= 0; i--,j--) {//從b的尾部(即int值的低位)開始copy數據
      if(j >= 0)
         a[i] = b[j];
      else
         a[i] = 0;//如果b.length不足4,則將高位補0
  }
int v0 = (a[0] & 0xff) << 24;//&0xff將byte值無差異轉成int,避免Java自動類型提升后,會保留高位的符號位
int v1 = (a[1] & 0xff) << 16;
int v2 = (a[2] & 0xff) << 8;
int v3 = (a[3] & 0xff) ;
return v0 + v1 + v2 + v3;
}
short和byte的互轉

/**
  * 轉換short為byte
  *
  * @param b
  * @param s 需要轉換的short
  * @param index
  */
public static void putShort(byte b[], short s, int index) {
   b[index + 1] = (byte) (s >> 8);
   b[index + 0] = (byte) (s >> 0);
}

/**
  * 通過byte數組取到short
  *
  * @param b
  * @param index 第幾位開始取
  * @return
  */
public static short getShort(byte[] b, int index) {
   return (short) (((b[index + 1] << 8) | b[index + 0] & 0xff));
}
byte和char類型的轉換

/**
  * 字符到字節轉換
  *
  * @param ch
  * @return
  */
public static void putChar(byte[] bb, char ch, int index) {
      int temp = (int) ch;
      // byte[] b = new byte[2];
      for (int i = 0; i < 2; i ++ ) {
         // 將最高位保存在最低位
         bb[index + i] = new Integer(temp & 0xff).byteValue();
         temp = temp >> 8; // 向右移8位
      }
}

/**
  * 字節到字符轉換
  *
  * @param b
  * @return
  */
public static char getChar(byte[] b, int index) {
      int s = 0;
      if (b[index + 1] > 0)
         s += b[index + 1];
      else
         s += 256 + b[index + 0];
      s *= 256;
      if (b[index + 0] > 0)
         s += b[index + 1];
      else
         s += 256 + b[index + 0];
      char ch = (char) s;
      return ch;
}
byte和float的轉換

/**
  * float轉換byte
  *
  * @param bb
  * @param x
  * @param index
  */
public static void putFloat(byte[] bb, float x, int index) {
      // byte[] b = new byte[4];
      int l = Float.floatToIntBits(x);
      for (int i = 0; i < 4; i++) {
         bb[index + i] = new Integer(l).byteValue();
         l = l >> 8;
      }
}

/**
  * 通過byte數組取得float
  *
  * @param bb
  * @param index
  * @return
  */
public static float getFloat(byte[] b, int index) {
      int l;
      l = b[index + 0];
      l &= 0xff;
      l |= ((long) b[index + 1] << 8);
      l &= 0xffff;
      l |= ((long) b[index + 2] << 16);
      l &= 0xffffff;
      l |= ((long) b[index + 3] << 24);
      return Float.intBitsToFloat(l);
}
byte和double轉換

/**
  * double轉換byte
  *
  * @param bb
  * @param x
  * @param index
  */
public static void putDouble(byte[] bb, double x, int index) {
      // byte[] b = new byte[8];
      long l = Double.doubleToLongBits(x);
      for (int i = 0; i < 4; i++) {
         bb[index + i] = new Long(l).byteValue();
         l = l >> 8;
      }
}

/**
  * 通過byte數組取得float
  *
  * @param bb
  * @param index
  * @return
  */
public static double getDouble(byte[] b, int index) {
      long l;
      l = b[0];
      l &= 0xff;
      l |= ((long) b[1] << 8);
      l &= 0xffff;
      l |= ((long) b[2] << 16);
      l &= 0xffffff;
      l |= ((long) b[3] << 24);
      l &= 0xffffffffl;
      l |= ((long) b[4] << 32);
      l &= 0xffffffffffl;
      l |= ((long) b[5] << 40);
      l &= 0xffffffffffffl;
      l |= ((long) b[6] << 48);
      l &= 0xffffffffffffffl;
      l |= ((long) b[7] << 56);
      return Double.longBitsToDouble(l);
}
}

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