java - Can't dispose of jframe window? -

i'm trying dispose of difficulty window after 1 of difficulty button's clicked won't happen. i've tried .dispose , frame.setdefaultcloseoperation(jframe.exit_on_close); can't it. placement or more?

import java.awt.flowlayout; import java.awt.event.*; import javax.swing.jbutton; import javax.swing.jdialog; import javax.swing.jframe; import javax.swing.jlabel; import javax.swing.joptionpane; import javax.swing.jtextfield; import java.awt.event.actionevent; import java.awt.event.actionlistener; import java.awt.gridlayout;  public class game extends jframe{      public static jframe frame = new jframe();       private jlabel lab;  public static void main(string[] args) {      game difficulty = new game();     difficulty.setsize(350,105);     difficulty.settitle("difficulty.");     difficulty.setvisible(true);     difficulty.setlocationrelativeto(null);       /**game sudoku = new game();     sudoku.setsize(900, 900);     sudoku.setvisible(false);*/  }      public game(){      setlayout(new flowlayout());     lab = new jlabel("please select difficulty.");     add(lab);      jbutton easy;     easy = new jbutton("easy");     add(easy);       easy.addactionlistener(new actionlistener() {              public void actionperformed(actionevent e)             {                 //execute when button pressed                 system.out.println("you clicked button");                 jframe.dispose();             }         });          jbutton medium;     medium = new jbutton("medium");     add(medium);      jbutton hard;     hard = new jbutton("hard");     add(hard);      jbutton evil;     evil = new jbutton("evil!");     add(evil);  } } 

dispose() method not static, it'll not work calling directly jframe class

jframe.dispose(); 

try :

dispose(); 

or dispose frame object have created

frame.dispose(); 

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