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。