java - Why does the first panel added to a frame disappear? -


below example of adding 2 panels frame. 1 panel (the 2nd, red panel) appears.

disappearing panel in frame

why first panel disappear?

import java.awt.*; import javax.swing.*; import javax.swing.border.emptyborder;  public class disappearingpanelinframe {      disappearingpanelinframe() {         jframe f = new jframe(this.getclass().getsimplename());         f.setdefaultcloseoperation(jframe.dispose_on_close);          f.add(new coloredpanel(color.green));         f.add(new coloredpanel(color.red));          f.pack();         f.setvisible(true);     }      public static void main(string[] args) {         runnable r = new runnable() {             @override             public void run() {                 new disappearingpanelinframe();             }         };         swingutilities.invokelater(r);     } }  class coloredpanel extends jpanel {      coloredpanel(color color) {         setbackground(color);         setborder(new emptyborder(20, 150, 20, 150));     } }

  • the default layout of jframe (or more in case, content pane of frame) borderlayout.
  • when adding component bordelayout no constraint, swing api put component in center.
  • a borderlayout can contain one component in each of 5 layout constraints.
  • when second component added same (in case center) constraint of borderlayout, implementation of java display last component added.

as better approach depends on specific needs of user interface.


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