分解质因数(如:90=二*3*3*5)

分解质因数(如:90=2*3*3*5)
    分解质因数:如90=2*3*3*5,代码如下:

package com.flyingh.demo;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Demo {

	public static void main(String[] args) throws NumberFormatException,
			IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		System.out.println("请输入一个正整数:");
		int n = Integer.parseInt(br.readLine());
		System.out.println(n + "=" + getOut(n));
	}

	private static StringBuilder sb = new StringBuilder();

	private static String getOut(int n) {
		if (!isPrime(n)) {
			for (int i = 2; i < n; i++) {
				if (isPrime(i) && n % i == 0) {
					sb.append(i).append("*");
					return getOut(n / i);
				}
			}
		} else {
			sb.append(n);
		}
		return sb.toString();
	}

	private static boolean isPrime(int n) {
		// TODO Auto-generated method stub
		if (n == 1) {
			throw new IllegalArgumentException("参数不能为1");
		}
		if (n == 2 || n == 3) {
			return true;
		}
		for (int j = 2; j <= Math.sqrt(n); j++) {
			if (n % j == 0) {
				return false;
			}
		}
		return true;
	}

}

    当输入108时,运行结果如下:

108=2*2*3*3*3