做的程式有時候會需要用到,

記錄下

public class NumberUtil {
	/**
	 * int整數轉換為4位元組的byte陣列
	 * 
	 * @param i
	 *            整數
	 * @return byte陣列
	 */
	public static byte[] intToByte4(int i) {
		byte[] targets = new byte[4];
		targets[3] = (byte) (i & 0xFF);
		targets[2] = (byte) (i >> 8 & 0xFF);
		targets[1] = (byte) (i >> 16 & 0xFF);
		targets[0] = (byte) (i >> 24 & 0xFF);
		return targets;
	}

	/**
	 * long整數轉換為8位元組的byte陣列
	 * 
	 * @param lo
	 *            long整數
	 * @return byte陣列
	 */
	public static byte[] longToByte8(long lo) {
		byte[] targets = new byte[8];
		for (int i = 0; i < 8; i++) {
			int offset = (targets.length - 1 - i) * 8;
			targets[i] = (byte) ((lo >>> offset) & 0xFF);
		}
		return targets;
	}

	/**
	 * short整數轉換為2位元組的byte陣列
	 * 
	 * @param s
	 *            short整數
	 * @return byte陣列
	 */
	public static byte[] unsignedShortToByte2(int s) {
		byte[] targets = new byte[2];
		targets[0] = (byte) (s >> 8 & 0xFF);
		targets[1] = (byte) (s & 0xFF);
		return targets;
	}

	/**
	 * byte陣列轉換為無符號short整數
	 * 
	 * @param bytes
	 *            byte陣列
	 * @return short整數
	 */
	public static int byte2ToUnsignedShort(byte[] bytes) {
		return byte2ToUnsignedShort(bytes, 0);
	}

	/**
	 * byte陣列轉換為無符號short整數
	 * 
	 * @param bytes
	 *            byte陣列
	 * @param off
	 *            開始位置
	 * @return short整數
	 */
	public static int byte2ToUnsignedShort(byte[] bytes, int off) {
		int high = bytes[off];
		int low = bytes[off + 1];
		return (high << 8 & 0xFF00) | (low & 0xFF);
	}

	/**
	 * byte陣列轉換為int整數
	 * 
	 * @param bytes
	 *            byte陣列
	 * @param off
	 *            開始位置
	 * @return int整數
	 */
	public static int byte4ToInt(byte[] bytes, int off) {
		int b0 = bytes[off] & 0xFF;
		int b1 = bytes[off + 1] & 0xFF;
		int b2 = bytes[off + 2] & 0xFF;
		int b3 = bytes[off + 3] & 0xFF;
		return (b0 << 24) | (b1 << 16) | (b2 << 8) | b3;
	}
}