java - JFrame components being able to call paintComponent through repaint, although using flowlayout -

i have jframe in flowlayout multiple jlabels added it, when call repaint on jlabels, paintcomponent not being called. if remove flowlayout, last jlabel added shows , repaints properly. tried use panel didn't work. i'm not sure i'm using though.

import java.awt.dimension; import java.awt.eventqueue; import java.awt.flowlayout; import java.awt.toolkit; import javax.swing.jframe;  public class racingletters {      public static void main(string[] args) {          eventqueue.invokelater(new runnable() {             public void run() {                 final jframe jframe = new jframe();                 jframe.settitle("racing letters");                 jframe.setdefaultcloseoperation(jframe.exit_on_close);                 //jframe.setextendedstate(frame.maximized_both);                 dimension dimension = toolkit.getdefaulttoolkit().getscreensize();                 int x = (int) ((dimension.getwidth() - jframe.getwidth()) / 2);                 int y = (int) ((dimension.getheight() - jframe.getheight()) / 2);                 jframe.setlocation(x, y);                 jframe.setminimumsize(new dimension(500, 200));                 flowlayout fl = new flowlayout();                 jframe.setlayout(fl);                 //jframe.setlayout(null);                 jframe.setvisible(true);                      stringbuffer[] stringbufferarray = new stringbuffer[20];                 char ch = 'a';                  int yy = 20;                 (int = 0; < 5; i++) {                     stringbufferarray[i] = new stringbuffer("");                     bufferthread bt = new bufferthread(stringbufferarray[i], ch, 10, yy);                     //pane.add(bt);                     jframe.add(bt);                      new thread(bt).start();                     ch++;                     yy += 20;                 }              }         });      } } 

..

import java.awt.font; import java.awt.graphics; import java.awt.graphics2d; import java.util.random; import java.util.logging.level; import java.util.logging.logger; import javax.swing.jlabel;   public class bufferthread extends jlabel implements runnable {      char ch;     stringbuffer sb;     int x,y;      bufferthread(stringbuffer sb, char ch,int x, int y) {         this.sb = sb;         this.ch = ch;         this.x = x;         this.y = y;     }      @override     public void run() {         random rand = new random();          (int = 0; < 5; i++) {             sb.append(ch);             system.out.println(x + " " + y + " " + ch);             repaint();              try {                 thread.sleep(rand.nextint(500));             } catch (interruptedexception ex) {                 logger.getlogger(bufferthread.class.getname()).log(level.severe, null, ex);             }         }     }      public void paintcomponent(graphics g) {         //system.out.println(x + " " + y + " " + ch);         //system.out.println("aaaa");         //stem.out.println(sb);         graphics2d g2 = (graphics2d) g;          font f = new font("serif", font.plain, 24);         //if (sb.tostring().indexof("e") < 0)             g2.drawstring(sb.tostring(), x, y);      }  } 

the core problem jlabel isn't providing information frame's layout manager how big be. nor telling frame's layout manager it's updated , needs resized.

why you're trying paint text on label beyond me, seen that's label design.

you should avoid using thread when dealing swing components , should use javax.swing.timer , swingworker possible.

import java.awt.eventqueue; import java.awt.flowlayout; import java.awt.event.actionevent; import java.awt.event.actionlistener; import javax.swing.jframe; import javax.swing.jlabel; import javax.swing.timer; import javax.swing.uimanager; import javax.swing.unsupportedlookandfeelexception;  public class ticker {      public static void main(string[] args) {         new ticker();     }      public ticker() {         eventqueue.invokelater(new runnable() {             @override             public void run() {                 try {                     uimanager.setlookandfeel(uimanager.getsystemlookandfeelclassname());                 } catch (classnotfoundexception ex) {                 } catch (instantiationexception ex) {                 } catch (illegalaccessexception ex) {                 } catch (unsupportedlookandfeelexception ex) {                 }                  jframe frame = new jframe("test");                 frame.setdefaultcloseoperation(jframe.exit_on_close);                 frame.setlayout(new flowlayout());                 frame.add(new tickerlabel());                 frame.setsize(100, 100);                 frame.setlocationrelativeto(null);                 frame.setvisible(true);             }          });     }      public class tickerlabel extends jlabel {          private int counter;          public tickerlabel() {             timer timer = new timer(500, new actionlistener() {                 @override                 public void actionperformed(actionevent e) {                     if (counter > 4) {                         ((timer)e.getsource()).stop();                     } else {                         string text = gettext();                         text += (char)(((int)'a') + counter);                         settext(text);                     }                     counter++;                 }             });             timer.setrepeats(true);             timer.setcoalesce(true);             timer.start();         }      }  }