java 使用JFrame的GUI;动作侦听器和事件处理程序

Posted 2021-05-07

import javax.swing.*;

class First{
    public static void main(String args[]) {

        // Creating an object for the Second class
        Second secondObject = new Second();
        // when hitting the X button the window will close
        secondObject.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        // setting the size of the window
        secondObject.setSize(350, 100);
        // setting the visibility of the window
        secondObject.setVisible(true);


    }
}

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.JPasswordField;
import javax.swing.JOptionPane;

// Inheriting JFrame methods
public class Second extends JFrame{

    // creating Textfield variables
    private JTextField item1, item2, item3;
    // creating password variable
    private JPasswordField passwordField;

    // making a constructor for the GUI
    public Second(){
        // setting the title
        super("Title");
        setLayout(new FlowLayout());

        // variable assigned to a textfield
        item1 = new JTextField(10);
        // adding the variable
        add(item1);

        // variable assigned to a textfield with default text in it
        item2 = new JTextField("Enter Text Here");
        // adding the variable
        add(item2);

        // variable assigned to textfield with default text in it
        item3 = new JTextField("Uneditable", 20);
        // making the textfield uneditable
        item3.setEditable(false);
        // adding the variable
        add(item3);

        //  variable assigned to password with default password in it
        passwordField = new JPasswordField("mypass");
        // adding the variable
        add(passwordField);

        // Creating an object because .addActionListener only takes on object as its argument
        thehandler handler = new thehandler();
        item1.addActionListener(handler);
        item2.addActionListener(handler);
        item3.addActionListener(handler);
        passwordField.addActionListener(handler);
    }

    // Creating the event handling class which implements ActionListener
    private class thehandler implements ActionListener{
        public void actionPerformed(ActionEvent event){

            String string = "";

            // checking if the source of the event is one of the variables and giving an output for each of them
            if (event.getSource() == item1){
                string = String.format("Field 1: %s", event.getActionCommand());
            } else if (event.getSource() == item2){
                string = String.format("Field 2: %s", event.getActionCommand());
            } else if(event.getSource() == item3){
                string = String.format("Field 3: %s", event.getActionCommand());
            } else if(event.getSource() ==  passwordField){
                string = String.format("Password field is: %s", event.getActionCommand());
            }

            // positioning the message dialog in the center of the screen and showing the string
            JOptionPane.showMessageDialog(null, string);
        }
    }
}