java - Selecting text in JTextArea does not show any selection color -


i have piece of code in jtextarea added jframe. whenever user presses ↑ key content of jtextarea should selected.

here code

import javax.swing.*; import java.awt.event.keyevent; import java.awt.event.keyadapter;  public class selectiontest extends keyadapter {     final jtextarea jtextarea;     public static void main(string[] args)     {         new selectiontest();     }      selectiontest()     {         jframe jframe=new jframe();         jframe.setlocationrelativeto(null);         jframe.setdefaultcloseoperation(windowconstants.exit_on_close);         jtextarea = new jtextarea("test 1-2-3");         jtextarea.addkeylistener(this);         jframe.add(jtextarea);         jframe.pack();         jframe.setvisible(true);     }      @override     public void keypressed(keyevent e)     {         if( e.getkeycode() != keyevent.vk_up ) return;         jtextarea.selectall();     } }

however observe nothing selected on pressing ↑ key, instead if change method keypressed following, works.

@override public void keypressed(keyevent e) {     if( e.getkeycode() != keyevent.vk_up ) return;     swingutilities.invokelater(new runnable()     {         @override         public void run()         {             jtextarea.selectall();         }     }); }

i want know reason behaviour. threading issue ?

jtextarea uses arrow keys moving caret. you're interfering it. why invokelater() helps.

also, have make sure component focusable , has focus. key listener lower level interface. mention above in comments, better use key bindings instead. see how use key bindings details , examples.

here example based on posted code uses key bindings : 

import javax.swing.*;  import java.awt.event.actionevent; import java.awt.event.keyevent; import java.awt.event.keyadapter;  public class selectiontest extends keyadapter {     final jtextarea jtextarea;     public static void main(string[] args)     {         new selectiontest();     }      selectiontest()     {         jframe jframe=new jframe();         jframe.setlocationrelativeto(null);         jframe.setdefaultcloseoperation(windowconstants.exit_on_close);         jtextarea = new jtextarea("test 1-2-3");          action someaction = new abstractaction() {             public void actionperformed(actionevent e) {                 jtextarea.selectall();             }         };         jtextarea.getinputmap().put(                 keystroke.getkeystroke(keyevent.vk_up, 0), "someaction");         jtextarea.getactionmap().put("someaction", someaction);          jframe.add(jtextarea);         jframe.pack();         jframe.setvisible(true);     } }

also note if text area looses focus may not show selection. may need add jtextarea.requestfocusinwindow() before altering selection. there selectall() may use select text. see bug 4320295 : select , selectall don't work on jtextarea details.


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