java - Adding JPanel to JFrame? -

i'm trying add jlabel jpanel jframe. set border jpanel, see on jframe small black square in center of frame. whatever can't change size or location of it. please help.

    start main = new start();     random random = new random();      jframe mainframe = new jframe("mainframe");     jpanel mainpanel = new jpanel();     jlabel welcomelabel = new jlabel();      mainframe.add(main);     mainframe.setlayout(new gridbaglayout());     mainframe.setdefaultcloseoperation(jframe.exit_on_close);     mainframe.settitle(names[random.nextint(names.length)]);     mainframe.pack();     mainframe.setvisible(true);     mainframe.setsize(mainframex, mainframey);     mainframe.setresizable(false);     mainframe.setlocationrelativeto(null);     mainframe.add(mainpanel);      mainpanel.add(welcomelabel);     mainpanel.setborder(new lineborder(color.black));     mainpanel.setsize(new dimension(200, 200));      welcomelabel.setfont(new font("verdana", 1, 20));     welcomelabel.setlocation(100, 100);      main.start(); 

suggestions:

• you want read tutorial, laying out components, explain how code swing layout managers, , information essential solve current problem.
• one caveat: urge avoid temptation use null layout use of lead creation of code hard maintain or upgrade.
• your jlabel, welcomelabel, of course need text visible.
• don't set it's location via setlocation(...) again use layout managers dirty work of placing , sizing components.
• you want call pack() , setvisible(true) on jframe after adding initial components.