Swing组件的构造函数

先看一下效果



啥也不说了，直接上程序对比。

程序1：

import java.awt.BorderLayout;
import java.awt.Dimension;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;

public class Client extends JFrame{
private JTextField textField;
private JTextArea textArea;

public Client(){
setTitle("客户端");
setBounds(100, 100, 373, 257);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

final JPanel panel = new JPanel();
this.add(panel,BorderLayout.NORTH);

final JLabel label = new JLabel();
label.setText("路径：");
panel.add(label);

textField = new JTextField();
textField.setPreferredSize(new Dimension(140, 25));
panel.add(textField);

final JButton button = new JButton();
button.setText("选择视频");
panel.add(button);

final JButton button2 = new JButton();
button2.setText("发送");
panel.add(button2);

final JScrollPane scrollPane = new JScrollPane();
this.add(scrollPane,BorderLayout.CENTER);

textArea = new JTextArea();
scrollPane.setViewportView(textArea);
}

public static void main(String[] args) {
Client client = new Client();
client.setVisible(true);
}
}

程序2：

import java.awt.BorderLayout;
import java.awt.Dimension;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;

public class Client extends JFrame{
private JTextField textField;
private JTextArea textArea;

public Client(){
final JPanel panel = new JPanel();

final JLabel label = new JLabel();
label.setText("路径：");
panel.add(label);

textField = new JTextField();
textField.setPreferredSize(new Dimension(140, 25));
panel.add(textField);

final JButton button = new JButton();
button.setText("选择视频");
panel.add(button);

final JButton button2 = new JButton();
button2.setText("发送");
panel.add(button2);

this.add(panel,BorderLayout.NORTH);

final JScrollPane scrollPane = new JScrollPane();

textArea = new JTextArea();
scrollPane.setViewportView(textArea);

this.add(scrollPane,BorderLayout.CENTER);

setTitle("客户端");
setBounds(100, 100, 373, 257);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setVisible(true);
}

public static void main(String[] args) {
Client client = new Client();
}
}

显著的区别：

1. setVisible（）位置不同。

2.构造函数中，组件的添加顺序不同。程序1按照从小到大的顺序，程序2按照从大到小的顺序。

程序1必须在构造对象之后，使用setVisible方法，否则无法正常显示组件。原因不详。