CODEWITHSUNDEEP
javauser-interfaceswingjscrollpanejtextarea
Amit
Amit

Reputation: 34735

How to set AUTO-SCROLLING of JTextArea in Java GUI?

I have embedded a JTextArea on a JScrollPane and am using that JTextArea for output.

I want that whenever the ouput goes beyond the size of the JTextArea, the JTextArea scrolls automatically so that user don't have to do manual scroll down to see the recent output.

How can I do that?

I have already set the autoscroll property of both JTextArea and JScrollPane to true.

Upvotes: 70

Views: 106719

Answers (8)

Chandra_lal
Chandra_lal

Reputation: 61

Best and easiest way, Try this :

  import javax.swing.text.DefaultCaret;
  DefaultCaret caret = (DefaultCaret) textArea.getCaret();
  caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);

Upvotes: 0

camickr
camickr

Reputation: 324118

When using JDK1.4.2 (or earlier) the most common suggestion you will find in the forums is to use code like the following:

textArea.append(...);
textArea.setCaretPosition(textArea.getDocument().getLength());

However, I have just noticed that in JDK5 this issue has actually been resolved by an API change. You can now control this behaviour by setting a property on the DefaultCaret of the text area. Using this approach the code would be:

JTextArea textArea = new JTextArea();
DefaultCaret caret = (DefaultCaret)textArea.getCaret();
caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);

Note:

The above suggestion to set the caret update policy does not work.

Instead you may want to check out Smart Scrolling which gives the user the ability to determine when scrolling should be automatic or not.

A more detailed description of automatic scrolling in a text area can be found here: Text Area Scrolling

Upvotes: 153

HAig
HAig

Reputation: 21

I tried most suggestions but ran into problems when the content of the JTextArea becomes large (several MB). Finally the following showed best performance:

myTextArea.append( someText );
myTextArea.getCaret().setDot( Integer.MAX_VALUE );

Of course, any selection the user had made gets lost. Hence, its only usable for a "display-only" usage of the text area.

Still, in my installation, if the content of the JTextArea exceeds some 9MB, it gets kind of unusable (very sluggish to almost frozen GUI).

A similar phenomenon occurs when the text contains characters that are represented by two chars (two 16-bit units) in the UTF-16 encoding (so-called surrogate pairs, like this: 🌹). I have a solution for filtering, but maybe a different topic.

Upvotes: 2

Honest
Honest

Reputation: 192

Try this:

JTextArea jTextArea = new JTextArea();
JScrollPane jScrollPane = new JScrollPane();
jScrollPane.setViewport(jTextArea);

Upvotes: -3

JavaBeginner
JavaBeginner

Reputation: 7

Use this instead

JTextArea textArea = new JTextArea();
DefaultCaret caret = (DefaultCaret)textArea.getCaret();
caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);
scrollPane = new JScrollPane();
scrollPane.add(textArea);
scrollPane.setViewportView(textArea);

Upvotes: -2

kayz1
kayz1

Reputation: 7434

    JTextArea jTextArea = new JTextArea();
    DefaultCaret caret = (DefaultCaret)jTextArea.getCaret();
    caret.setUpdatePolicy(DefaultCaret.OUT_BOTTOM);

Upvotes: 2

ton1
ton1

Reputation: 7628

When you click anywhere over JTextArea, auto-scrolling have possible to be stopped. Because the position of caret once changed, view point changed too. In this time you should set caret position when you append or add some text. On my way, I made method including set caret position, and then use it when anything to be added or appended.

Upvotes: 2

user211233
user211233

Reputation: 31

    JScrollBar vbar = scrollPane.getVerticalScrollBar();

    for (int i = 0; i < 20; i++) {

        myJTxt.append("This is text " + i + "\n");
        vbar.setValue(vbar.getMaximum());
        vbar.paint(vbar.getGraphics());
        myJTxt.scrollRectToVisible(myJTxt.getVisibleRect());
        myJTxt.paint(myJTxt.getGraphics());
        try {
            Thread.sleep(250);
        } catch (InterruptedException ex) {
            Logger.getLogger(ScrollTextView.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

Upvotes: 2

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