Java中的消息对话框 (GUI)

消息对话框向用户提供信息。消息对话框是使用 JOptionPane.showMessageDialog() 方法创建的。

我们调用 JOptionPane 类的静态 showMessageDialog()方法来创建消息对话框。我们提供对话框的父级、消息文本、标题和消息类型。消息类型是以下常量之一：

1. 错误信息
2. 警告信息
3. QUESTION_MESSAGE
4. INFORMATION_MESSAGE

使用方法：

1. setLayout(…):方法帮助我们设置容器的布局，通常是一个 JPanel，比如 FlowLayout、BorderLayout、GridLayout、null 布局，或者我们想在容器上添加的任何布局。
2. setBounds(…)：方法用于设置JButton等组件的位置和大小，只有在JFrame中使用空布局时才有用。
3. setVisible(…)：方法用于设置 JFrame 的 Visibility 状态。
   1. setVisible(true) 将设置 JFrame 对用户可见。
   2. setVisible(false) 将设置 JFrame 对用户不可见。
4. getSource()：事件对象包含对生成事件的组件的引用。要从事件对象中提取该引用，我们使用 getSource() 方法。
5. add()：用于将 JButton 等组件添加到 JFrame 的容器中。

下面是上面讨论的显示消息对话框的方法的实现：

Java

// Java program to show ERROR_MESSAGE dialog
// in Java. Importing different Package.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
class Demo extends JFrame implements ActionListener
{
    // Declaration of object of JButton class.
    JButton b1;
     
    // Constructor of Demo class
    Demo()
    {
        // Setting layout as null of JFrame.
        this.setLayout(null);
         
        // Initialization of object of "JButton" class.
        b1 = new JButton("Button 1");
         
        // Setting Bounds of a JButton.
        b1.setBounds(130, 05, 100, 50);
         
        //"this" keyword in java refers to current object.
        // Adding JButton on JFrame.
        this.add(b1);
         
        // Adding Listener toJButton.
        b1.addActionListener(this);
    }
 
    // Override Method
    public void actionPerformed(ActionEvent evt)
    {
        if (evt.getSource() == b1)
        {
            // Code To popup an ERROR_MESSAGE Dialog.
            JOptionPane.showMessageDialog(this, "Enter a valid Number",
                                   "ERROR", JOptionPane.ERROR_MESSAGE);
        }
    }
}
 
class MessageDialogs1 {
     
    // Driver code
    public static void main(String args[])
    {
        // Creating Object of demo class.
        Demo f = new Demo();
         
        // Setting Bounds of a Frame.
        f.setBounds(200, 200, 400, 300);
         
        // Setting Resizable status of frame as false
        f.setResizable(false);
         
        // Setting Visible status of frame as true.
        f.setVisible(true);
    }
}

输出 ：

Java

// Java program to show WARNING_MESSAGE dialog
// in Java. Importing different Package.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
class Demo extends JFrame implements ActionListener
{
    // Declaration of object of JButton class.
    JButton b1;
     
    // Constructor of Demo class
    Demo()
    {
        // Setting layout as null of JFrame.
        this.setLayout(null);
         
        // Initialization of object of "JButton" class.
        b1 = new JButton("Button 2");
         
        // Setting Bounds of a JButton.
        b1.setBounds(130, 05, 100, 50);
         
        //"this" keyword in java refers to current object.
        // Adding JButton on JFrame.
        this.add(b1);
         
        // Adding Listener toJButton.
        b1.addActionListener(this);
    }
 
    // Override Method
    public void actionPerformed(ActionEvent evt)
    {
        if (evt.getSource() == b1) {
             
            // Code To popup an WARNING_MESSAGE Dialog.
            JOptionPane.showMessageDialog(this, "Enter a valid String",
                               "WARNING", JOptionPane.WARNING_MESSAGE);
        }
    }
}
 
class MessageDialogs2 {
     
    // Driver code
    public static void main(String args[])
    {
        // Creating Object of demo class.
        Demo f = new Demo();
         
        // Setting Bounds of a Frame.
        f.setBounds(200, 200, 400, 300);
         
        // Setting Resizable status of frame as false
        f.setResizable(false);
         
        // Setting Visible status of frame as true.
        f.setVisible(true);
    }
}

输出 ：

Java

// Java program to show QUESTION_MESSAGE
// dialog in Java. Importing different Package.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
class Demo extends JFrame implements ActionListener
{
    // Declaration of object of JButton class.
    JButton b1;
     
    // Constructor of Demo class
    Demo()
    {
        // Setting layout as null of JFrame.
        this.setLayout(null);
         
        // Initialization of object of "JButton" class.
        b1 = new JButton("Button 3");
         
        // Setting Bounds of a JButton.
        b1.setBounds(130, 05, 100, 50);
         
        //"this" keyword in java refers to current object.
        // Adding JButton on JFrame.
        this.add(b1);
         
        // Adding Listener toJButton.
        b1.addActionListener(this);
    }
 
    // Override Method
    public void actionPerformed(ActionEvent evt)
    {
        if (evt.getSource() == b1)
        {
            // Code TO popup a QUESTION_MESSAGE Dialog.
            JOptionPane.showMessageDialog(this, "Do you want to quit",
                             "Question", JOptionPane.QUESTION_MESSAGE);
        }
    }
}
 
class MessageDialogs3 {
     
    // Driver code
    public static void main(String args[])
    {
        // Creating Object of demo class.
        Demo f = new Demo();
         
        // Setting Bounds of a Frame.
        f.setBounds(200, 200, 400, 300);
         
        // Setting Resizable status of frame as false
        f.setResizable(false);
         
        // Setting Visible status of frame as true.
        f.setVisible(true);
    }
}

输出 ：

Java

// Java program to show INFORMATION_MESSAGE
// dialog in Java. Importing different Package.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
class Demo extends JFrame implements ActionListener
{
    // Declaration of object of JButton class.
    JButton b1;
     
    // Constructor of Demo class
    Demo()
    {
        // Setting layout as null of JFrame.
        this.setLayout(null);
         
        // Initialization of object of "JButton" class.
        b1 = new JButton("Button 4");
         
        // Setting Bounds of a JButton.
        b1.setBounds(130, 05, 100, 50);
         
        //"this" keyword in java refers to current object.
        // Adding JButton on JFrame.
        this.add(b1);
         
        // Adding Listener toJButton.
        b1.addActionListener(this);
    }
 
    // Override Method
    public void actionPerformed(ActionEvent evt)
    {
        if (evt.getSource() == b1)
        {
            // Code To popup an INFORMATION_MESSAGE Dialog.
            JOptionPane.showMessageDialog(this, "You Pressed Button FOUR",
                                          "INFORMATION",
                                          JOptionPane.INFORMATION_MESSAGE);
        }
    }
}
 
class MessageDialogs4 {
     
    // Driver code
    public static void main(String args[])
    {
         
        // Creating Object of demo class.
        Demo f = new Demo();
         
        // Setting Bounds of a Frame.
        f.setBounds(200, 200, 400, 300);
         
        // Setting Resizable status of frame as false
        f.setResizable(false);
         
        // Setting Visible status of frame as true.
        f.setVisible(true);
    }
}

输出 ：