ok, i'm creating tic tac toe gui. having working frame of 3x3 buttons change either x or o. issue implementing jlabel on top of buttons. label keeps track of who's turn , change either "o's turn" or "x's turn" can't seem jlabel update (only spouts errors). here's portion of code showing how trying implement this. program runs fine add (turn.settext("o's turn");) errors.
any feedback why may not working appreciated.
import java.awt.borderlayout; import java.awt.gridlayout; import java.awt.event.actionevent; import java.awt.event.actionlistener; import javax.swing.jframe; import javax.swing.jlabel; import javax.swing.jpanel; public class tictactoe extends jframe { xobutton[] xob = new xobutton[9]; private jlabel turn; public static int state; public tictactoe() { super("tictactoe"); //add xobuttons panel jpanel center = new jpanel(); state = 0; jlabel turn = new jlabel("x's turn"); center.setlayout(new gridlayout(3, 3, 2, 2)); //action listener buttonlistener bl = new buttonlistener(); (int = 0; < 9; i++) { xob[i] = new xobutton(); xob[i].addactionlistener(bl); center.add(xob[i]); } //add panel frame setlayout(new borderlayout()); add(center, borderlayout.center); add(turn, borderlayout.north); } //inner action listener class private class buttonlistener implements actionlistener { @override public void actionperformed(actionevent ae) { (int = 0; < 9; i++) { if(ae.getsource() == xob[i] && xob[i].getstate() == xobutton.none && state == 0) { xob[i].setstate(xobutton.x); state = 1; //turn.settext("o's turn"); } else if(ae.getsource() == xob[i] && xob[i].getstate() == xobutton.none && state == 1) { xob[i].setstate(xobutton.o); state = 0; } } } } }
guess: error nullpointerexception because turn null. solution: don't shadow variable. in other words you're re-declaring turn variable in constructor leaving field null.
e.g.,
public class tictactoe extends jframe{ xobutton[] xob = new xobutton[9]; private jlabel turn; public static int state; public tictactoe() { super("tictactoe"); //add xobuttons panel jpanel center = new jpanel(); state = 0; jlabel turn = new jlabel("x's turn"); // **** you're re-declaring turn here! better:
public class tictactoe extends jframe{ xobutton[] xob = new xobutton[9]; private jlabel turn; public static int state; public tictactoe() { super("tictactoe"); //add xobuttons panel jpanel center = new jpanel(); state = 0; turn = new jlabel("x's turn"); // **** note difference? in future, if have similar problems, please post entire error message , indicate line throws exception immensely!
