显示一个 window 以获取用户输入

Question

我是 Java 编程新手。

我有这两个小项目。

import javax.swing.*;

public class tutorial {

    public static void main(String[] args){
        JFrame frame = new JFrame("Test");
        frame.setVisible(true);
        frame.setSize(300,300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JLabel label = new JLabel("hello");
        JPanel panel = new JPanel();
        frame.add(panel);
        panel.add(label);

        JButton button = new JButton("Hello again");
        panel.add(button);
    }
}

还有这个：

import java.util.*;

public class Test {

    public static void main(String[] args){
        int age;
        Scanner keyboard = new Scanner(System.in);
        System.out.println("How old are you?");
        age = keyboard.nextInt();
        if (age<18) 
        {
            System.out.println("Hi youngster!");
        }
        else 
        {
            System.out.println("Hello mature!");
        }
    }

}

如何将第二个代码添加到第一个代码中，以便用户看到 window 上面写着 'How old are you' 并且他们可以输入他们的年龄。

提前致谢！

Answer 1

这不是一个简单的问题，因为您在一个示例中使用命令行，而在另一个示例中使用 Swing GUI。

这是一个工作示例，我在这里和那里发表了评论。这与 java 最佳实践相去甚远，它错过了很多验证（看看当您在文本字段中输入几个字母或什么都不输入时会发生什么。

另外请忽略 setLayout(null) 和 setBounds() 语句，这只是一个不使用任何布局管理器的简单示例。

希望我的评论能帮助您发现java！

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.*;

//You'll need to implement the ActionListener to listen to buttonclicks
public class Age implements ActionListener{

    //Declare class variables so you can use them in different functions
    JLabel label;
    JTextField textfield;

    //Don't do al your code in the static main function, instead create an instance
    public static void main(String[] args){
        new Age();
    }

    // this constructor is called when you create a new Age(); like in the main function above.
    public Age()
    {
        JFrame frame = new JFrame("Test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(300,300);
        frame.setLayout(null);

        JPanel panel = new JPanel();
        panel.setBounds(0,0,300,300);
        panel.setLayout(null);

        label = new JLabel("hello");
        label.setBounds(5,5,100,20);

        // a JTextfield allows the user to edit the text in the field.
        textfield = new JTextField();
        textfield.setBounds(5,30,100,20);

        JButton button = new JButton("Hello again");
        button.setBounds(130,30,100,20);
        // Add this instance as the actionlistener, when the button is clicked, function actionPerformed will be called.
        button.addActionListener(this);

        panel.add(label);
        panel.add(textfield);
        panel.add(button);

        frame.add(panel);
        frame.setVisible(true);
    }

    //Required function actionPerformed for ActionListener. When the button is clicked, this function is called.
    @Override
    public void actionPerformed(ActionEvent e)
    {
        // get the text from the input.
        String text = textfield.getText();

        // parse the integer value from the string (! needs validation for wrong inputs !)
        int age = Integer.parseInt(text);
        if (age<18) 
        {
            //instead of writing out, update the text of the label.
            label.setText("Hi youngster!");
        }
        else 
        {
            label.setText("Hello mature!");
        }
    }
}

Answer 2

so that the user will see a window that says 'How old are you' and they can type their age.

最简单的开始方法是使用 JOptionPane。查看 Swing 教程中关于 How to Use Dialogs 的部分以获取示例和解释。

关于 Swing 的基本信息，请不要忘记查看其他 Swing 相关主题的 table 内容。

Answer 3

您将需要一个输入字段来获取文本，然后将 ActionListener 添加到包含按下按钮时执行的逻辑的按钮。

我修改了您的代码以实现您所描述的内容：

import javax.swing.*;
import java.awt.event.*;

public class tutorial {

    public static void main(String[] args) {
        JFrame frame = new JFrame("Test");
        frame.setVisible(true);
        frame.setSize(300, 300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JLabel label = new JLabel("hello");
        JPanel panel = new JPanel();
        frame.add(panel);
        panel.add(label);

        final JTextField input = new JTextField(5); // The input field with a width of 5 columns
        panel.add(input);

        JButton button = new JButton("Hello again");
        panel.add(button);

        final JLabel output = new JLabel(); // A label for your output
        panel.add(output);

        button.addActionListener(new ActionListener() { // The action listener which notices when the button is pressed
            public void actionPerformed(ActionEvent e) {
                String inputText = input.getText();
                int age = Integer.parseInt(inputText);
                if (age < 18) {
                    output.setText("Hi youngster!");
                } else {
                    output.setText("Hello mature!");
                }
            }
        });
    }
}

在该示例中，我们不验证输入。所以如果输入不是 Integer Integer.parseInt 将抛出异常。组件也没有很好地排列。但是为了一开始就保持简单，应该这样做。 :)

Answer 4

我不确定你想要的所有东西，因为它是未定义的，但据我所知，你想要一个包含输入字段的 JFrame，你将能够在其中输入值并显示适当的答案。我还建议您阅读教程，但如果您有任何疑问，请不要犹豫。我希望它有点接近你想要的。

package example.tutorial;

import java.awt.BorderLayout;
import java.awt.FlowLayout;
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;

public class Tutorial extends JPanel {
    private static final String YOUNG_RESPONSE = "Hi youngster!";
    private static final String ADULT_RESPONSE = "Hello mature!";
    private static final String INVALID_AGE = "Invalid age!";

    private static final int MIN_AGE = 0;
    private static final int MAX_AGE = 100;

    private static JTextField ageField;
    private static JLabel res;

    private Tutorial() {
        setLayout(new BorderLayout());

        JPanel northPanel = new JPanel();
        northPanel.setLayout(new FlowLayout());
        JLabel label = new JLabel("How old are you ? ");
        northPanel.add(label);

        ageField = new JTextField(15);
        northPanel.add(ageField);
        add(northPanel, BorderLayout.NORTH);


        JPanel centerPanel = new JPanel();  
        JButton btn = new JButton("Hello again");
        btn.addActionListener(new BtnListener());
        centerPanel.add(btn);

        res = new JLabel();
        res.setVisible(false);
        centerPanel.add(res);

        add(centerPanel, BorderLayout.CENTER);
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("Test");
        frame.add(new Tutorial());
        frame.setVisible(true);
        frame.setSize(300, 300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    private static class BtnListener implements ActionListener {
        @Override
        public void actionPerformed(ActionEvent e) {
            String content = ageField.getText();
            int age = -1;
            try{
                age = Integer.parseInt(content);
                if(isValid(age)) {
                    res.setText(age < 18 ? YOUNG_RESPONSE : ADULT_RESPONSE);
                } else {
                    res.setText(INVALID_AGE);
                }
                if(!res.isVisible())
                    res.setVisible(true);
            } catch(NumberFormatException ex) {
                res.setText("Wrong input");
            }
        }

        private boolean isValid(int age) {
            return age > MIN_AGE && age < MAX_AGE;
        }
    }
}

显示一个 window 以获取用户输入

Display a window to obtain user input

java

swing

frame