【JAVA语言程序设计基础篇】--事件驱动程序设计--贷款计算器

输入年份 利率 总金额 ，计算出总还款数 每月还款数

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{@Overridepublic 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;  }}

点击computer payment生成数据