Java 练习题

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编写一个 Application 并定义一个异常类，要求完成如下操作。定义一个 money 类，包括：
存款余额：成员变量 yu；
存款操作：方法 putMoney(double money)
取款操作：方法 getMoney(double money)
获取余额：方法 getYu()
如果存款余额小于取款额时，显示当前余额，并告之不能取款，否则显示取款成功的信息。

public class Exercise {    public static void main(String[] args) {        Money money = new Money();        money.putMoney(1000);        try {            money.getMoney(500);        } catch (MoneyException e) {            System.out.println("当前余额为：" + money.getYu() + " 不能取款");        }    }}class MoneyException extends Exception {    MoneyException() {    }}class Money {    private double yu = 0;    public void putMoney(double money) {        yu = yu + money;        System.out.println("存款成功！");    }    public void getMoney(double money) throws MoneyException{        if (!(yu >= money))            throw new MoneyException();        yu = yu - money;        System.out.println("取款成功！");    }    public double getYu() {        return yu;    }}

实现两个定时器，一个线程每隔 1s 显示一次，一个线程每隔 3s 显示一次。

public class Exercise {    public static void main(String[] args) {        Thread1 thread1 = new Thread1();        Thread2 thread2 = new Thread2();        thread1.start();        thread2.start();    }}class Thread1 extends Thread {    public void run() {        while (true) {            System.out.println("第一个线程！");            try {                sleep(1000);            } catch (InterruptedException e) {                e.printStackTrace();            }        }    }}class Thread2 extends Thread {    public void run() {        while (true) {            System.out.println("第二个线程！");            try {                sleep(3000);            } catch (InterruptedException e) {                e.printStackTrace();            }        }    }}

编写一个类，类名为 MulThread，定义含一个字符串参数的构造方法，并实现 Runnable 接口，接口中的 run() 方法如下实现，方法先在命令行显示该线程信息，然后随机休眠小于 1s 的时间，最后显示线程结束信息：finished + 线程名。编写一个 Application 程序，创建 MulThread 类的 3 个线程对象 t1, t2, t3，并再启动这 3 个线程。

public class Exercise {    public static void main(String[] args) {        MulThread th1 = new MulThread("th1");        MulThread th2 = new MulThread("th2");        MulThread th3 = new MulThread("th3");        Thread t1 = new Thread(th1);        Thread t2 = new Thread(th2);        Thread t3 = new Thread(th3);        t1.start();        t2.start();        t3.start();    }}class MulThread implements Runnable {    private String string;    MulThread (String str) {        string = str;    }    public void run() {        System.out.println(string);        try {            Thread.sleep((int)(Math.random() * 1000));        } catch (InterruptedException e) {            e.printStackTrace();        }        System.out.println("Finished " + string);    }}

设计一个窗口，内含一个按钮。开始运行时，按钮显示 “click me ！” 字样，但按下按钮时，按钮上面的文字变成 “click me again ！”，再按一次，则会变成 “click me ！”。如此循环。

import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import javax.swing.JButton;import javax.swing.JFrame;public class Exercise {    public static void main(String[] args) {        new Windows();    }}class Windows extends JFrame {    JButton button;    public Windows(){        button = new JButton("Click Me");        this.add(button);        button.addActionListener(new ActionListener() {            @Override            public void actionPerformed(ActionEvent actionEvent) {                if(button.getText().equals("Click Me")){                    button.setText("Click Me Again");                }                else button.setText("Click Me");            }        });        this.setVisible(true);        this.setBounds(50,50,200,150);        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);    }}

编写一个应用程序，设计 4 个按钮，分别明明 “加”，“减”，“乘”，“除”；有三个文本框。单击相应的按钮，将两个文本框的数字做运算，在第三个文本框中显示结果。

import java.awt.Color;import java.awt.Dimension;import java.awt.FlowLayout;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import javax.swing.Box;import javax.swing.JButton;import javax.swing.JFrame;import javax.swing.JOptionPane;import javax.swing.JTextField;public class Exercise {    public static void main(String[] args) {        new Calculaor();    }}class Calculaor implements ActionListener{    private JButton jb1,jb2,jb3,jb4;    private JTextField jt1,jt2,jt3;    private JFrame jf;    private Box box1,box2,basebox;    public Calculaor(){        jf=new JFrame("简单计算器");        jf.setBounds(300, 300, 440, 130);        jf.setVisible(true);        jf.setLayout(new FlowLayout());        jb1 = new JButton("加");        jb2 = new JButton("减");        jb3 = new JButton("乘");        jb4 = new JButton("除");        jb1.addActionListener(this);        jb2.addActionListener(this);        jb3.addActionListener(this);        jb4.addActionListener(this);        jt1 = new JTextField(" ");        jt2 = new JTextField(" ");        jt3 = new JTextField(" ");        Dimension dim = new Dimension(100, 20);        Dimension dim2 = new Dimension(180, 20);        jt1.setPreferredSize(dim);        jt2.setPreferredSize(dim);        jt3.setPreferredSize(dim2);        jt3.setEditable(false);        jt3.setBackground(Color.gray);        box1 = Box.createHorizontalBox();        box1.add(jt1);        box1.add(Box.createHorizontalStrut(10));        box1.add(jt2);        box1.add(Box.createHorizontalStrut(10));        box1.add(jt3);        box2 = Box.createHorizontalBox();        box2.add(jb1);        box2.add(Box.createHorizontalStrut(10));        box2.add(jb2);        box2.add(Box.createHorizontalStrut(10));        box2.add(jb3);        box2.add(Box.createHorizontalStrut(10));        box2.add(jb4);        basebox = Box.createVerticalBox();        basebox.add(box1);        basebox.add(Box.createVerticalStrut(10));        basebox.add(box2);        jf.add(basebox);        jf.validate();        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);    }    public void actionPerformed(ActionEvent e) {        String temp1 = jt1.getText().trim();        String temp2 = jt2.getText().trim();        if(temp1.equals("")||temp2.equals("")){            JOptionPane.showMessageDialog(jf,"文本框不能为空。");        }else{            double a = 0, b = 0;            try{                a = Double.parseDouble(temp1);                b = Double.parseDouble(temp2);            }catch(Exception e1){                JOptionPane.showMessageDialog(jf,"您输入了非法字符,请输入正确的数字。");                return;            }            if(e.getSource() == jb1){                jt3.setText(""+(a + b));                System.out.println("" + (a + b));            }else if(e.getSource() == jb2){                jt3.setText("" + (a - b));            }else if(e.getSource() == jb3){                jt3.setText("" + (a * b));            }else if(e.getSource() == jb4){                jt3.setText("" + (a / b));            }        }    }}

编写一个图形用户界面的应用程序，包括两个文本框和一个按钮，当单击按钮时，可以把一个文本框中的内容复制到另一个文本框中。

import javax.swing.*;import java.awt.*;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;public class Exercise {    public static void main(String[] args) {        new Windows();    }}class Windows extends JFrame {    JButton button = new JButton("Add");    JTextField textField1 = new JTextField(30);    JTextField textField2 = new JTextField(30);    public Windows() {        Container app = this.getContentPane();        BoxLayout boxLayout = new BoxLayout(app, BoxLayout.X_AXIS);        setLayout(boxLayout);        add(textField1);        JPanel panel = new JPanel();        panel.add(button);        add(panel);        add(textField2);        button.addActionListener(new ActionListener() {            @Override            public void actionPerformed(ActionEvent actionEvent) {                if (textField1.getText().length() > 0) {                    textField2.setText(textField2.getText() + textField1.getText() + "\n");                    textField1.setText("");                }            }        });        setVisible(true);        pack();        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);    }}

编写一个应用程序，要求有一个含有菜单的窗口，窗口中有文本区组件。菜单有 “打开文件” 的菜单项，当单击菜单项时，使用输入流将一个名为 “hello.txt” 文件的内容读入到文本区。

import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import java.io.*;import javax.swing.*;public class Exercise {    public static void main(String[] args) throws IOException{        File file = new File("hello.txt");        FileOutputStream out = new FileOutputStream(file);        String st = new String("This is a string of characters!");        byte[] bytes = st.getBytes("UTF-8");        out.write(bytes);        out.flush();        out.close();        new Window();    }}class Window extends JFrame {    JTextArea textArea = new JTextArea(20, 30);    public Window() throws IOException{        setLayout(new BoxLayout(getContentPane(), BoxLayout.Y_AXIS));        JMenuBar menuBar = new JMenuBar();        JButton openFile = new JButton("Open File");        menuBar.add(openFile);        add(menuBar);        add(textArea);        openFile.addActionListener(new ActionListener() {            @Override            public void actionPerformed(ActionEvent actionEvent) {                File file = new File("hello.txt");                FileInputStream in = null;                try {                    in = new FileInputStream(file);                } catch (FileNotFoundException e) {                    e.printStackTrace();                }                byte[] bytes = new byte[1024];                try {                    while (in.read(bytes) != -1) {                        textArea.setText(new String(bytes));                    }                } catch (IOException e) {                    e.printStackTrace();                }                try {                    in.close();                } catch (IOException e) {                    e.printStackTrace();                }            }        });        setVisible(true);        pack();        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);    }}

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