Question

java-swing 给文本区jtextarea怎么加个滚动条？

package processhomework;
import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.Color;
public class first extends JFrame{
private JLabel jLabel;
private JTextField jTextField;
private JButton jButton,jButton1,jButton2;
private JTextArea jtextarea;
private JScrollPane sp;

public first()
{
super();
this.setSize(700, 500);
this.getContentPane().setLayout(null);
this.add(getJLabel(), null);
this.add(getJTextField(), null);
this.add(getJButtonok(), null);
this.add(getJButtoncancel(),null);
this.add(getJButtonzero(),null);
this.setBackground(Color.red);
this.add(getJTextArea(), null);

this.setTitle("calculator");
}
private JTextArea getJTextArea(){
if(jtextarea==null){
jtextarea=new JTextArea();
jtextarea.setBounds(5, 45, 650, 400);
}
jtextarea.setLineWrap(true);
//sp=new JScrollPane(jtextarea);
//sp.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
return jtextarea;
}
private JLabel getJLabel() {
if(jLabel == null) {
jLabel = new javax.swing.JLabel();
jLabel.setBounds(10, 10, 150, 30);
jLabel.setText("请输入需要输出的位数：");
}

return jLabel;
}
private JTextField getJTextField() {
if(jTextField == null) {
jTextField = new javax.swing.JTextField();
jTextField.setBounds(150, 10, 160, 30);
}
return jTextField;
}
private JButton getJButtonok() {
if(jButton == null) {
jButton = new javax.swing.JButton();
jButton.setBounds(400, 10, 100,30);
jButton.setText("begin");
}
return jButton;
}
private JButton getJButtoncancel() {
if(jButton1 == null) {
jButton1 = new JButton();
jButton1.setBounds(530, 10, 100, 30);
jButton1.setText("stop");
}
return jButton1;
}
private JButton getJButtonzero() {
if(jButton2 == null) {
jButton2 = new JButton();
jButton2.setBounds(310, 10, 80, 30);
jButton2.setText("清零");
}
return jButton2;
}
public static void main(String[] args)
{
first w = new first();
w.setVisible(true);
}
}

Answer 1

private JScrollPane getJTextArea ()
{
	if (jtextarea == null)
	{
		jtextarea = new JTextArea ();
	}
	jtextarea.setLineWrap (true);
	jtextarea.setWrapStyleWord (true);
	sp = new JScrollPane (jtextarea);
	sp.setBounds (5, 45, 650, 400);
	return sp;
}

Answer 2

JTextArea放到 JScrollPane里。

追问

为什么是将JTextArea放到 JScrollPane里，而不是将JScroltArea放到 lPaneJTex里呢？

追答

JScrollPane为JTextArea提供滚动条属于装饰模式