• 本例演示如何编写程序来计算贷款支付问题。
• 下面是编写程序的步骤：
• 1.提示用户输入年利率、年数和贷款总额
• 2.利用年利率算出月利率
• 3.通过前面的公式计算月支付额。
• 4.计算总支付额，它是月支付额乘以12再乘以年数。
• 5.在消息对话框中显示月支付额和总支付额。

package cn.hncu.Chapter2;

import javax.swing.JOptionPane;

/**

 * @author hncu_chx

 *

 * Mylove amin

 *

 */

public class ComputeLoan {

    public static void main(String[] args) {

        //Enter yearly interest rate开始的年利率

        String annualInterestRateString = JOptionPane.showInputDialog("Enter yearly " +

                "interest rate,for example 8.25:");

        //Convert转换… string to double

        double annualInterestRate =

                Double.parseDouble(annualInterestRateString);

        //Obtain获得 monthly每月的 interest rate利息率

        double monthlyInterestRate = annualInterestRate/1200;

        //Enter number of years

        String numberOfYearsString =JOptionPane.showInputDialog("Enter number of years as an integer," +

                "\nfor example 5:");

        //Convert转换 string to int

        int numberOfYears = Integer.parseInt(numberOfYearsString);

        //Enter开始 loan借款 amount总额

        String loanString = JOptionPane.showInputDialog("Enter loan amount," +

                "for example 120000.95:");

        //Convert string to double

        double loanAmount = Double.parseDouble(loanString);

        //Calculate 计算 payment付款，支付；报酬

        double monthlyPayment = loanAmount * monthlyInterestRate/(1-1/Math.pow(1+monthlyInterestRate,

                numberOfYears*12));

        double totalPayment = monthlyPayment*numberOfYears*12;

        //Format格式 to keep tow digits位数 数字 after the decimal小数 point点

        //格式保留小数点后两位数

        monthlyPayment = (int )(monthlyPayment *100)/100.0;

        totalPayment = (int)(totalPayment *100)/100.0;

        //Display显示 results结果 成绩

        String output = "The monthly payment is "+monthlyPayment+

                "\nThe total payment is "+totalPayment;

        JOptionPane.showMessageDialog(null, output);

    }

}

注意：如果在输入对话框中点击取消，无字符串返回，系统会出现运行时错误。