【JAVA语言程序设计基础篇】--事件驱动程序设计--贷款计算器

package chapter16;

import java.awt.BorderLayout;
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;//
import javax.swing.border.TitledBorder;

@SuppressWarnings("serial")
public class LoanCalculator extends JFrame{
private JTextField AnnualInterestRate = new JTextField();
private JTextField numberOfYears = new JTextField();
private JTextField LoanAmount = new JTextField();
private JTextField MonthlyPayment = new JTextField();
private JTextField TotalPayment = new JTextField();
public LoanCalculator(){

JPanel p1 = new JPanel();
p1.setLayout(new GridLayout(5,2));
p1.add(new JLabel("annual interest rate"));
p1.add(AnnualInterestRate);
p1.add(new JLabel("number of years"));
p1.add(numberOfYears);
p1.add(new JLabel("loan amount"));
p1.add(LoanAmount);
p1.add(new JLabel("monthly payment"));
p1.add(MonthlyPayment);
p1.add(new JLabel("totalpayment"));
p1.add(TotalPayment);
p1.setBorder(new TitledBorder("enter loan amount,interest rate,and year"));

JPanel p2 = new JPanel();
p2.setLayout(new FlowLayout(FlowLayout.RIGHT));
JButton button = new JButton("computer payment");
p2.add(button,BorderLayout.SOUTH);

add(p1,BorderLayout.CENTER);//需要在这里加入方位
add(p2,BorderLayout.SOUTH);

button.addActionListener(new buttonListener());

}
public static void main(String[] args) {
JFrame frame = new LoanCalculator();
frame.setTitle("loancalculator");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
frame.pack();
frame.setSize(300, 300);
}
class buttonListener implements ActionListener{

@Override
public void actionPerformed(ActionEvent e) {

double interest = Double.parseDouble(AnnualInterestRate.getText());
double loanamount = Double.parseDouble(LoanAmount.getText());
int year = Integer.parseInt(numberOfYears.getText());

Loan loan = new Loan(interest,year,loanamount);

MonthlyPayment.setText(String.format("%.2f", loan.getMonthlyPayment()));//why is no useful in Line 61？？
TotalPayment.setText(String.format("%.2f", loan.getTotalPayment()));

}
}
}

class Loan {
private double annualInterestRate;
private int numberOfYears;
private double loanAmount;
private java.util.Date loanDate;

/** Default constructor */
public Loan() {
this(2.5, 1, 1000);
}

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

/** Return annualInterestRate */
public double getAnnualInterestRate() {
return annualInterestRate;
}

/** Set a new annualInterestRate */
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 loanAmount */
public double getLoanAmount() {
return loanAmount;
}

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

/** Find monthly payment */
public double getMonthlyPayment() {
double monthlyInterestRate = annualInterestRate / 1200;
double monthlyPayment = loanAmount * monthlyInterestRate / (1 -
(Math.pow(1 / (1 + monthlyInterestRate), numberOfYears * 12)));
return monthlyPayment;
}

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

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