11.19. JTextArea

A JTextArea provides an area for manipulating multiple lines of text. Like class JTextField , JTextArea is a subclass of JTextComponent , which declares common methods for JTextFields , JTextArea s and several other text-based GUI components .

The application in Fig. 11.47 and Fig. 11.48 demonstrates JTextArea s. One JTextArea displays text that the user can select. The other JTextArea is uneditable and is used to display the text the user selected in the first JTextArea . Unlike JTextFields , JTextArea s do not have action events. As with multiple-selection JLists (Section 11.12), an external event from another GUI component indicates when to process the text in a JTextArea . For example, when typing an e-mail message, you normally click a Send button to send the text of the message to the recipient. Similarly, when editing a document in a word processor, you normally save the file by selecting a Save or Save As... menu item. In this program, the button Copy >>> generates the external event that copies the selected text in the left JTextArea and displays it in the right JTextArea .

Figure 11.47. Copying selected text from one JTextArea to another.

1

// Fig. 11.47: TextAreaFrame.java

2

// Copying selected text from one textarea to another.

3

import

java.awt.event.ActionListener;
 4

import

java.awt.event.ActionEvent;
 5

import

javax.swing.Box;
 6

import

javax.swing.JFrame;
 7


import

javax.swing.JTextArea;

8

import

javax.swing.JButton;
 9


import

javax.swing.JScrollPane;

10
11

public class

TextAreaFrame

extends

JFrame
12  {
13


private

JTextArea textArea1;

// displays demo string


14


private

JTextArea textArea2;

// highlighted text is copied here


15

private

JButton copyJButton;

// initiates copying of text

16
17

// no-argument constructor

18

public

TextAreaFrame()
19     {
20

super

(

"TextArea Demo"

);
21

Box box = Box.createHorizontalBox();

// create box


22        String demo =

"This is a demo string to\n"

+
23

"illustrate copying text\nfrom one textarea to \n"

+
24

"another textarea using an\nexternal event\n"

;
25
26

textArea1 =

new

JTextArea( demo,

10

,

15

);

// create textarea1


27

box.add(

new

JScrollPane( textArea1 ) );

// add scrollpane


28
29        copyJButton =

new

JButton(

"Copy >>>"

);

// create copy button

30

box.add( copyJButton );

// add copy button to box


31        copyJButton.addActionListener(
32
33

new

ActionListener()

// anonymous inner class

34           {
35

// set text in textArea2 to selected text from textArea1

36

public void

actionPerformed( ActionEvent event )
37              {
38

textArea2.setText( textArea1.getSelectedText() );

39              }

// end method actionPerformed

40           }

// end anonymous inner class

41        );

// end call to addActionListener

42
43

textArea2 =

new

JTextArea(

10

,

15

);

// create second textarea


44

textArea2.setEditable(

false

);

// disable editing


45

box.add(

new

JScrollPane( textArea2 ) );

// add scrollpane


46
47        add( box );

// add box to frame

48     }

// end TextAreaFrame constructor

49  }

// end class TextAreaFrame

Figure 11.48. Test class for TextAreaFrame .

1

// Fig. 11.48: TextAreaDemo.java

2

// Copying selected text from one textarea to another.

3

import

javax.swing.JFrame;
 4
 5

public class

TextAreaDemo
 6  {
 7

public static void

main( String args[] )
 8     {
 9        TextAreaFrame textAreaFrame =

new

TextAreaFrame();
10        textAreaFrame.setDefaultCloseOperation(

JFrame.EXIT_ON_CLOSE

);
11        textAreaFrame.setSize(

425

,

200

);

// set frame size

12        textAreaFrame.setVisible(

true

);

// display frame

13     }

// end main

14  }

// end class TextAreaDemo

In the constructor (lines 1848), line 21 creates a Box container (package javax.swing ) to organize the GUI components. Box is a subclass of Container that uses a BoxLayout layout manager (discussed in detail in Section 22.9) to arrange the GUI components either horizontally or vertically. Box 's static method createHorizontalBox creates a Box that arranges components from left to right in the order that they are attached.

Lines 26 and 43 create JTextArea s textArea1 and textArea2 . Line 26 uses JTextArea 's three-argument constructor, which takes a String representing the initial text and two int s specifying that the JTextArea has 10 rows and 15 columns . Line 43 uses JTextArea 's two-argument constructor, specifying that the JTextArea has 10 rows and 15 columns. Line 26 specifies that demo should be displayed as the default JTextArea content. A JTextArea does not provide scrollbars if it cannot display its complete contents. So, line 27 creates a JScrollPane object, initializes it with textArea1 and attaches it to container box . By default, horizontal and vertical scrollbars will appear as necessary in a JScrollPane .

Lines 2941 create JButton object copyButton with the label "Copy >>>" , add copyButton to container box and register the event handler for copyButton 's ActionEvent . This button provides the external event that determines when the program should copy the selected text in textArea1 to textArea2 . When the user clicks copyButton , line 38 in actionPerformed indicates that method getSelectedText (inherited into JTextArea from JTextComponent ) should return the selected text from textArea1 . The user selects text by dragging the mouse over the desired text to highlight it. Method setText changes the text in textArea2 to the string returned by getSelectedText .

Lines 4345 create textArea2 , set its editable property to false and add it to container box . Line 47 adds box to the JFrame . Recall from Section 11.17 that the default layout of a JFrame is a BorderLayout and that the add method by default attaches its argument to the CENTER of the BorderLayout .

It is sometimes desirable, when text reaches the right side of a JTextArea , to have the text wrap to the next line. This is referred to as line wrapping . By default, JTextArea does not wrap lines.

Look-and-Feel Observation 11.20

To provide line-wrapping functionality for a JTextArea , invoke JTextArea method setLineWrap with a TRue argument.

JScrollPane Scrollbar Policies

This example uses a JScrollPane to provide scrolling for a JTextArea . By default, JScrollPane displays scrollbars only if they are required. You can set the horizontal and vertical scrollbar policies of a JScrollPane when it is constructed . If a program has a reference to a JScrollPane , the program can use JScrollPane methods setHorizontalScrollBarPolicy and setVerticalScrollBarPolicy to change the scrollbar policies at any time. Class JScrollPane declares the constants

JScrollPane.VERTICAL_SCROLLBAR_ALWAYS


JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS

to indicate that a scrollbar should always appear, constants

JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED


JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED

to indicate that a scrollbar should appear only if necessary (the defaults) and constants

JScrollPane.VERTICAL_SCROLLBAR_NEVER


JScrollPane.HORIZONTAL_SCROLLBAR_NEVER

to indicate that a scrollbar should never appear. If the horizontal scrollbar policy is set to JScrollPane.HORIZONTAL_SCROLLBAR_NEVER , a JTextArea attached to the JScrollPane will automatically wrap lines.