一、計算需要多長時間才能夠儲存一定數量的退休金

import java.util.Scanner;

public class Retirement {

    public static void main(String[] args) {
        //read inputs
        Scanner in = new Scanner(System.in);

        System.out.print("你退休需要多少錢？");
        double goal = in.nextDouble();

        System.out.print("你每年的報酬是多少錢？"
 
);
        double payment = in.nextDouble();

        System.out.print("利率在%: ");
        double interestRate = in.nextDouble();

        double balance = 0;
        int years = 0;

        //在未達成目標時更新帳戶餘額
        while(balance < goal){
            //加上今年的付款和利息
            balance += payment;
            double
 
 interest = balance * interestRate / 100;
            balance += interest;
            years++;
        }

        System.out.println("你可以在"+years+"年內退休.");
    }

}

二、計算每年的餘額並由使用者決定是否滿足退休所用

import java.util.Scanner;

public class Retirement2 {

    public static void main(String[] args) {
        Scanner in
 
 = new Scanner(System.in);

        System.out.print("你每年的報酬是多少錢？");
        double payment = in.nextDouble();

        System.out.print("利率在%: ");
        double interestRate = in.nextDouble();

        double balance = 0;
        int year = 0;

        String input;

        //在未達成目標時更新帳戶餘額
        do{
            ////加上今年的付款和利息
            balance += payment;
            double interest = balance * interestRate / 100;
            balance += interest;
            year++;

            //列印當前賬戶餘額
            System.out.printf("在 %d年後,你的賬戶餘額是 %,.2f%n",year,balance);

            //詢問是否準備退休並獲得收入
            System.out.print("準備退休了嗎？(Y/N) ");
            input = in.next();
        }while(input.equals("N"));
    }

}

三、計算數字抽獎中獎的概率

import java.util.Scanner;

public class LotteryOdds {
    public static void main (String[] args){
        Scanner in = new Scanner(System.in);

        System.out.print("你要猜幾個數字？");
        int k = in.nextInt();

        System.out.print("你能猜的最高數字是多少？");
        int n = in.nextInt();

        /*
         * 計算二項式係數 n*(n-1)*(n-2)*...*(n-k+1)/(1*2*3*...*k)
         */
        int lotterOdds = 1;
        for(int i = 1;i<=k;i++){
            lotterOdds = lotterOdds * (n-i+1) / i;
        }
        System.out.println("你的中獎概率為1/"+lotterOdds+".祝你好運!");
    }
}