java - Background color does not change in bluej -


i have written code has label , button in frame. have changed background never changes. 

    import javax.swing.*;     import java.awt.*;      import javax.swing.border.*;     public class frames      {     jframe main_menu=new jframe("main menu");jframe circumference=new jframe("circumference");     jframe area=new jframe("area");jframe perimeter=new jframe("perimeter");jframe sets=new   jframe("sets");     jframe fundamental_oprations=new jframe("fundamental oprations");jframe power_and_roots=new jframe("power_and_roots");     void main_menu()     {         jpanel contentpane = (jpanel) main_menu.getcontentpane();         contentpane.setlayout(new borderlayout(10,10));         contentpane.setborder(new emptyborder(300, 150, 300, 150));         contentpane.setlayout(new gridlayout(4, 4));         jpanel buttonpanel = new jpanel(new gridlayout(8,8));         contentpane.add(labels.main_menu,borderlayout.north);         contentpane.add(buttons.sets,borderlayout.south);         main_menu.setbackground(color.yellow);         main_menu.pack();         main_menu.setvisible(true);       }       }

you should setting background color of content pane via getcontentpane().setbackground(color.yellow):

import java.awt.color; import java.awt.dimension; import java.awt.eventqueue;  import javax.swing.jframe;  public class frames extends jframe {     private static final long serialversionuid = 1l;      public static void main(string[] args) {         eventqueue.invokelater(new runnable() {             public void run() {                 try {                     new frames();                 } catch (exception e) {                     e.printstacktrace();                 }             }         });     }      public frames() {         setsize(new dimension(100, 100));         settitle("main menu");         getcontentpane().setbackground(color.yellow);         setvisible(true);     }  }

also, consider using variable naming conventions; instance, main_menu should named mainmenu.


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