public static void main(String[] args) {
		System.out.println(bili(2,6));
	}
	public static String bili(int a,int b) {
		int g=gcd(a,b);
		if(g!=0)
			return new StringBuilder().append((a/g)).append(":").append((b/g)).toString();
		else
			return null;
	}
	public static int gcd(int a,int b) {
        if(b==0) return a;
        return gcd(b,a%b);
    }

 输出：1:3