java练习 计算n位可被浮点数精确表示的小数

原理，穷举生成N-1位定点二进制小数（第N位为1），然后转换成十进制的就行了。

import java.util.Scanner;

public class GetDecimal {
	static Vector<int[]> record = null;

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		System.out.println("输入n,输出n位可被浮点数精确表示的小数");
		int len = sc.nextInt();
		if (len == 1)
			System.out.println(0.5);
		else
			f(len - 1);

	}

	public static void f(int len) {
		double dec = 0;
		int max = (int) Math.pow(2, len) - 1;
		for (int i = 0; i <= max; i++) {
			dec = getSum(getBinString(i, len) + "1");
			System.out.println(dec);
		}
	}

	// 转换成二进制字符串
	public static String getBinString(int i, int len) {
		StringBuffer str = new StringBuffer(Integer.toString(i, 2));
		for (int j = 0; str.length() != len; j++) {
			str.insert(0, "0");
		}
		return str.toString();
	}

	// 计算值
	public static double getSum(String s) {
		double sum = 0;
		for (int i = 0; i < s.length(); i++) {
			if (s.charAt(i) == '1') {
				sum += Math.pow(2, -(i + 1));
			}
		}
		return sum;
	}
}