Java--类和对象 --实例学习

贷款类：loan

1.创建2个class。TestLoanClass 和 Loan

2.在TestLoanClass类 中，写入代码：

package com.algorithm.java.blueBirdge;

import javax.swing.*;

//JOptionPane消息提示框

public class TestLoanClass {
    public static void main(String args[]) {
        //JOptionPane消息提示框
        //enter yearly interest rate
        String annualInterestRateString = JOptionPane.showInputDialog(
                // JOptionPane.showInputDialog方法返回用户输入的字符串。
                "Enter yearly interestrate,for example 8.25:"
        );

        //Convert string to double

        //Double.parseDouble方法是把数字类型的字符串，转换成double类型
        //Double.valueOf方法是把数字类型的字符串，转换成Double类型
        double annualInterestRate = Double.parseDouble(annualInterestRateString);

        //enter number of years

        String numberOfYearString = JOptionPane.showInputDialog(
                // JOptionPane.showInputDialog方法返回用户输入的字符串。
                "Enter number of years as an integer,
for example 5:"
        );

        //Convert string to int
        int numberOfyears = Integer.parseInt(numberOfYearString);

        //enter loan amout
        String loanString = JOptionPane.showInputDialog(
                "Enter loan amout,for example 120000.95:"
        );

        //convert string to double
        double loanAmount = Double.parseDouble(loanString);

        //Create Loan object
        Loan loan = new Loan(annualInterestRate, numberOfyears, loanAmount);

        //Format to keep two digits after the decimal point
        double monthlyPayment = (int) (loan.getMonthlyPayment() * 100) / 100.0;
        double totalPayment = (int) (loan.getTotalPayment() * 100) / 100.0;

        //diaplay results
        String output = "The loan was create on " + loan.getLoanDate().toString() + "
The monthly payment is" + monthlyPayment + "
The total Payment is" + totalPayment;
        JOptionPane.showMessageDialog(null, output);
    }
}

3.在Loan类中插入代码：

package com.algorithm.java.blueBirdge;

import com.sun.xml.internal.ws.api.streaming.XMLStreamReaderFactory;

public class Loan {
    private double annualInterestRate;
    private int numberOfYears;
    private double loanAmount;
    private java.util.Date loanDate;//为什么这句话要写在类里面？？？？？？？？？？？？？

    /*Default constructor*/
    public Loan() {
        this(7.5, 30, 100000);
    }

    /*Construct a loan with specified annual interest rate,
     *  number of years and loan amout*/
    public Loan(double annualInterestRate, int numberOfYears, double loanAmount) {
        this.annualInterestRate = annualInterestRate;
        this.numberOfYears = numberOfYears;
        this.loanAmount = loanAmount;
        loanDate = new java.util.Date();//????????????????????????????????
    }

    //*************封装后的获取和修改********************
    /*return annualInteresRate*/
    public double getAnnualInterestRate() {
        return annualInterestRate;
    }

    /*Set a new annualInteresRate*/
    public void setAnnualInterestRate(double annualInterestRate) {
        this.annualInterestRate = annualInterestRate;
    }

    /*return numberOfYears*/
    public int getNumberOfYears() {
        return numberOfYears;
    }

    /*Set a new numberOfYears*/
    public void setNumberOfYears(int numberOfYears) {
        this.numberOfYears = numberOfYears;
    }

    /*return loanAmout*/
    public double getLoanAmount() {
        return loanAmount;
    }

    /*Set a new loanAmount*/
    public void setLoanAmount(double loanAmount) {
        this.loanAmount = loanAmount;
    }
    //*************************************************

    /*find Monthly payment*/
    public double getMonthlyPayment() {
        double mothlyInterestRate = annualInterestRate / 1200;
        return loanAmount * mothlyInterestRate / (1 - (Math.pow(1 / (1 + mothlyInterestRate), numberOfYears * 12)));

    }

    /*find total payment*/
    public double getTotalPayment() {
        return getMonthlyPayment() * numberOfYears * 12;
    }

    /*return loan date*/
    //?????????????????????????????
    public java.util.Date getLoanDate() {
        return loanDate;
    }
}

4.代码分析：
（1）代码部分出现了：private java.util.Date loanDate;写在类里面，是为了引入loanDate变量。同时，在构造方法中也出现：loanDate = new java.util.Date();

（2）Loan的数据域有 ：annualInterestRate,numberOfYears,loanAmount和loanDate

  Loan的数据域有:

getAnnualInterestRate(返回这笔贷款的年利率),getNumberOfYears（返回这笔贷款的年限）,getLoanAmount（返回这笔贷款额）,getLoanDate（返回这笔贷款发生日期）,

setAnnualInterstRate（设置这笔贷款新的年利率）,setNumberOfYears（设置这笔贷款新的贷款年限）,setLoanAmount（设置这笔贷款新的贷款额）,

getMonthlyPayment（返回这笔贷款的月支付额）和getTotalPayment（返回这笔贷款的总支付额）

5.测试结果：

6.测试成功！

 

package com.algorithm.java.blueBirdge;

import javax.swing.*;

//JOptionPane消息提示框

public class TestLoanClass {
    public static void main(String args[]) {
        //JOptionPane消息提示框
        //enter yearly interest rate
String annualInterestRateString = JOptionPane.showInputDialog(
                // JOptionPane.showInputDialog方法返回用户输入的字符串。
"Enter yearly interestrate,for example 8.25:"
);

        //Convert string to double

        //Double.parseDouble方法是把数字类型的字符串，转换成double类型
        //Double.valueOf方法是把数字类型的字符串，转换成Double类型
double annualInterestRate = Double.parseDouble(annualInterestRateString);

        //enter number of years

String numberOfYearString = JOptionPane.showInputDialog(
                // JOptionPane.showInputDialog方法返回用户输入的字符串。
"Enter number of years as an integer,
for example 5:"
);

        //Convert string to int
int numberOfyears = Integer.parseInt(numberOfYearString);

        //enter loan amout
String loanString = JOptionPane.showInputDialog(
                "Enter loan amout,for example 120000.95:"
);

        //convert string to double
double loanAmount = Double.parseDouble(loanString);

        //Create Loan object
Loan loan = new Loan(annualInterestRate, numberOfyears, loanAmount);

        //Format to keep two digits after the decimal point
double monthlyPayment = (int) (loan.getMonthlyPayment() * 100) / 100.0;
        double totalPayment = (int) (loan.getTotalPayment() * 100) / 100.0;

        //diaplay results
String output = "The loan was create on " + loan.getLoanDate().toString() + "
The monthly payment is" + monthlyPayment + "
The total Payment is" + totalPayment;
        JOptionPane.showMessageDialog(null, output);
    }
}