Java(图形用户界面)中的消息对话框
消息对话框向用户提供信息。消息对话框是用 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项、消息文本、标题和消息类型。消息类型是以下常量之一:
- 错误消息
- 警告消息
- 问题 _ 消息
- 信息 _ 消息
使用的方法:
- setLayout(…): 方法帮助我们设置容器的布局，通常是一个 JPanel，也就是说 FlowLayout、BorderLayout、GridLayout、null 布局，或者任何我们想在容器上添加的布局。
- setBounds(…): 方法用于设置像 JButton 这样的组件的位置和大小，只有在 JFrame 中使用 null 布局时才有用。
- 设置可见(…): 方法用于设置 JFrame 的可见性状态。
- setVisible(true)将设置用户可见的 JFrame。
- setVisible(false)将设置 JFrame 对用户不可见。
- getSource(): 事件对象包含对生成事件的组件的引用。为了从事件对象中提取该引用，我们使用 getSource()方法。
- add(): 用于向 JFrame 的容器中添加 JButton 等组件。
下面是上面讨论的显示消息对话框的方法的实现:
Java 语言(一种计算机语言，尤用于创建网站)
// 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 语言(一种计算机语言，尤用于创建网站)
// 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 语言(一种计算机语言，尤用于创建网站)
// 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 语言(一种计算机语言，尤用于创建网站)
// 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:
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