进制之间的转换

public class ToBin {
	public static void main(String[] args) {
		System.out.println("16的二进制为：" + toBin(16));
		System.out.println("16的十六进制为：" + toHex(16));
		System.out.println(toHex(255, 2, 1));
		System.out.println(toHex(255, 16, 4));
		System.out.println(toHex(255, 8, 3));
	}

	public static String toBin(int a) {
		StringBuilder sb = new StringBuilder();
		char[] chs = { '0', '1' };
		while (a != 0) {
			int b = a & 1;// 得到一个二进制位
			sb.append(chs[b]);
			a = a >>> 1;// 下一个二进制位
		}

		return sb.reverse().toString();
	}

	public static String toHex(int a) {
		StringBuilder sb = new StringBuilder();
		char[] chs = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };
		while (a != 0) {
			int b = a & 15; // 取最低4位
			sb.append(chs[b]);// b-10+'A'
			a = a >>> 4; // 下一个4位
		}
		return sb.reverse().toString();
	}

	public static String toHex(int a, int hex, int off) {
		if (a == 0) return "0";

		int base = -1;
		if (hex == 2)
			base = 1;
		else if (hex == 16)
			base = 15;// 1111
		else if (hex == 8) base = 7;// 111

		StringBuilder sb = new StringBuilder();
		char[] chs = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };
		while (a != 0) {
			int b = a & base; //取最低位
			sb.append(chs[b]);
			a = a >>> off;
		}
		return sb.reverse().toString();
	}
}