Hello, i have a problem with my code, it points out a Java.lang.NullPointerException error if i try to run it, could anybody try to help me?
import javax.swing.*; import java.awt.*; //Event brauchen wir für das Ereigniss, wenn ein Button geklickt wird import java.awt.event.*; public class secondgui extends JFrame { private JButton button; private JButton button1; private JButton button2; private JButton button3; private JButton button4; private JButton button5; private JButton button6; private JButton button7; private JButton button8; private JButton button9; private JButton button10; private JButton button11; private JButton button12; private JButton button13; private JButton button14; private JButton button15; private JButton button16; private JButton button17; private JButton button18; private JButton button19; private JButton button20; private JButton button21; private JButton button22; private JButton button23; private JButton button24; private JButton button25; private JButton button26; private JButton button27; private JButton button28; private JButton button29; private JButton button30; private JButton button31; private JButton button32; private JButton button33; private JButton button34; private JButton button35; private JButton button36; private JButton button37; private JButton button38; private JButton button39; private JButton button40; private JButton button41; private JButton button42; private JButton button43; private JButton button44; private JButton button45; private JButton button46; private JButton button47; private JButton button48; private JButton button49; private JButton button50; private JButton button51; private JButton button52; private JButton button53; private JButton button54; private JButton button55; private JButton button56; private JButton button57; private JButton button58; private JButton button59; private JButton button60; private JButton button61; private JButton button62; private JButton button63; private JButton button64; private JButton button65; private JButton button66; private JButton button67; private JButton button68; private JButton button69; private JButton button70; private JButton button71; private JButton button72; private JButton button73; private JButton button74; private JButton button75; private JButton button76; private JButton button77; private JButton button78; private JButton button79; private JButton button80; private JButton button81; private JPanel panelButton; private JLabel oben; private JButton anzeige; private String string; private String string2; private String string3; private String string4; private String string5; private String string6; private String string7; private String string8; private String string9; private String stringa; private int x1 =1; private int y1 =0; private int x2 =1; private int y2 =0; private int x3 =1; private int y3 =0; private int y4 =0; private int x4 =1; private int y5 =0; private int x5 =1; private int x6 =1; private int y6 =0; private int x7 =1; private int y7 =0; private int x8 =1; private int y8 =0; private int x9 = 1; private int y9 =0; private int o; private int q; int[][] sudo = {{1, 0, 0, 6, 0, 0, 0, 0, 0}, {0, 2, 0, 0, 0, 0, 9, 0, 0}, {0, 0, 3, 0, 0, 0, 0, 0, 0}, {0, 0, 0, 4, 0, 0, 0, 1, 0}, {0, 4, 0, 0, 5, 0, 0, 0, 0}, {0, 0, 0, 0, 0, 6, 0, 9, 0}, {0, 0, 2, 0, 0, 0, 7, 0, 0}, {0, 0, 0, 0, 0, 0, 0, 8, 0}, {3, 0, 0, 5, 0, 0, 0, 0, 9}}; public secondgui() { super("Sudoku"); setLocation(300,300); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //Das BorderLayout wird erzeugt getContentPane().setLayout(new BorderLayout(5,5)); //Buttons erzeugen button = new JButton("1"); button1 = new JButton("1"); button2 = new JButton("1"); button3 = new JButton("1"); button4 = new JButton("1"); button5 = new JButton("1"); button6 = new JButton("1"); button7 = new JButton("1"); button8 = new JButton("1"); button9 = new JButton("1"); button10 = new JButton("1"); button11 = new JButton("1"); button12 = new JButton("1"); button13 = new JButton("1"); button14 = new JButton("1"); button15 = new JButton("1"); button16 = new JButton("1"); button17 = new JButton("1"); button18 = new JButton("1"); button19 = new JButton("1"); button20 = new JButton("1"); button21 = new JButton("1"); button22 = new JButton("1"); button23 = new JButton("1"); button24 = new JButton("1"); button25 = new JButton("1"); button26 = new JButton("1"); button27 = new JButton("1"); button28 = new JButton("1"); button29 = new JButton("1"); button30= new JButton("1"); button31 = new JButton("1"); button32 = new JButton("1"); button33 = new JButton("1"); button34 = new JButton("1"); button35 = new JButton("1"); button36 = new JButton("1"); button37 = new JButton("1"); button38 = new JButton("1"); button39 = new JButton("1"); button40 = new JButton("1"); button41 = new JButton("1"); button42 = new JButton("1"); button43 = new JButton("1"); button44 = new JButton("1"); button45 = new JButton("1"); button46 = new JButton("1"); button47 = new JButton("1"); button48 = new JButton("1"); button49 = new JButton("1"); button50 = new JButton("1"); button51 = new JButton("1"); button52 = new JButton("1"); button53 = new JButton("1"); button54 = new JButton("1"); button55 = new JButton("1"); button56 = new JButton("1"); button57 = new JButton("1"); button58 = new JButton("1"); button59 = new JButton("1"); button60 = new JButton("1"); button61 = new JButton("1"); button62 = new JButton("1"); button63 = new JButton("1"); button64 = new JButton("1"); button65 = new JButton("1"); button66 = new JButton("1"); button67 = new JButton("1"); button68 = new JButton("1"); button69 = new JButton("1"); button70 = new JButton("1"); button71 = new JButton("1"); button72 = new JButton("1"); button73 = new JButton("1"); button74 = new JButton("1"); button75 = new JButton("1"); button76 = new JButton("1"); button77 = new JButton("1"); button78 = new JButton("1"); button79 = new JButton("1"); button80 = new JButton("1"); button81 = new JButton("1"); //Panels erzeugen auf einem GridLayout panelButton = new JPanel(new GridLayout(9,9)); //Auf Panel Buttons packen panelButton.add(button1); panelButton.add(button2); panelButton.add(button3); panelButton.add(button4); panelButton.add(button5); panelButton.add(button6); panelButton.add(button7); panelButton.add(button8); panelButton.add(button9); panelButton.add(button10); panelButton.add(button11); panelButton.add(button12); panelButton.add(button13); panelButton.add(button14); panelButton.add(button15); panelButton.add(button16); panelButton.add(button17); panelButton.add(button18); panelButton.add(button19); panelButton.add(button20); panelButton.add(button21); panelButton.add(button22); panelButton.add(button23); panelButton.add(button24); panelButton.add(button25); panelButton.add(button26); panelButton.add(button27); panelButton.add(button28); panelButton.add(button29); panelButton.add(button30); panelButton.add(button31); panelButton.add(button32); panelButton.add(button33); panelButton.add(button34); panelButton.add(button35); panelButton.add(button36); panelButton.add(button37); panelButton.add(button38); panelButton.add(button39); panelButton.add(button40); panelButton.add(button41); panelButton.add(button42); panelButton.add(button43); panelButton.add(button44); panelButton.add(button45); panelButton.add(button46); panelButton.add(button47); panelButton.add(button48); panelButton.add(button49); panelButton.add(button50); panelButton.add(button51); panelButton.add(button52); panelButton.add(button53); panelButton.add(button54); panelButton.add(button55); panelButton.add(button56); panelButton.add(button57); panelButton.add(button58); panelButton.add(button59); panelButton.add(button60); panelButton.add(button61); panelButton.add(button62); panelButton.add(button63); panelButton.add(button64); panelButton.add(button65); panelButton.add(button66); panelButton.add(button67); panelButton.add(button68); panelButton.add(button69); panelButton.add(button70); panelButton.add(button71); panelButton.add(button72); panelButton.add(button73); panelButton.add(button74); panelButton.add(button75); panelButton.add(button76); panelButton.add(button77); panelButton.add(button78); panelButton.add(button79); panelButton.add(button80); panelButton.add(button81); //Listener für Buttons addButtonListenerPruefen(anzeige); addButtonListener(button1); addButtonListener2(button2); addButtonListener3(button3); addButtonListener4(button4); addButtonListener5(button5); addButtonListener6(button6); addButtonListener7(button7); addButtonListener8(button8); addButtonListener9(button9); //Labels erzeugen oben = new JLabel("Sudoku"); //Label zentrieren oben.setHorizontalAlignment(JLabel.CENTER); anzeige = new JButton("Prüfen"); //Labels auf Frame packen (direkt auf das BorderLayout) getContentPane().add(BorderLayout.NORTH, oben); getContentPane().add(anzeige); //Panels auf Frame packen (das panelButton hat ein GridLayout, dass jetzt in den WestBereich des BorderLayouts kommt) getContentPane().add(BorderLayout.WEST, panelButton); getContentPane().add(BorderLayout.EAST, anzeige); pack(); setVisible(true); } public static void main(String[] args) { FirstGUI g = new FirstGUI(); } private void addButtonListener(JButton B)/>/> { b.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent ae) { eingabe(ae.getActionCommand()); int i = Integer.parseInt(button1.getText()); if (x1==1) { if (i<9) { i= i+1; String string = String.valueOf(i); button1.setText(string); y1= y1+1; } if (y1==8) { x1=0; y1=0; } } else { if (i>0) { i= i-1; String string = String.valueOf(i); button1.setText(string); y1= y1+1; } if (y1==8) { x1=1; y1=0; } } } }); } private void addButtonListener2(JButton B)/>/> { b.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent ae) { eingabe(ae.getActionCommand()); int h = Integer.parseInt(button2.getText()); if (x2==1) { if (h<9) { h= h+1; String string2 = String.valueOf(h); button2.setText(string2); y2= y2+1; } if (y2==8) { x2=0; y2=0; } } else { if (h>0) { h= h-1; String string2 = String.valueOf(h); button2.setText(string2); y2= y2+1; } if (y2==8) { x2=1; y2=0; } } } }); } private void addButtonListener3(JButton B)/>/> { b.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent ae) { eingabe(ae.getActionCommand()); int j = Integer.parseInt(button3.getText()); if (x3==1) { if (j<9) { j= j+1; String string3 = String.valueOf(j); button3.setText(string3); y3= y3+1; } if (y3==8) { x3=0; y3=0; } } else { if (j>0) { j= j-1; String string = String.valueOf(j); button3.setText(string); y3= y3+1; } if (y3==8) { x3=1; y3=0; } } } }); } private void addButtonListener4(JButton B)/>/> { b.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent ae) { eingabe(ae.getActionCommand()); int h = Integer.parseInt(button4.getText()); if (x4==1) { if (h<9) { h= h+1; String string4 = String.valueOf(h); button4.setText(string4); y4= y4+1; } if (y4==8) { x4=0; y4=0; } } else { if (h>0) { h= h-1; String string4 = String.valueOf(h); button4.setText(string4); y4= y4+1; } if (y4==8) { x4=1; y4=0; } } } }); } private void addButtonListener5(JButton B)/>/> { b.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent ae) { eingabe(ae.getActionCommand()); int h = Integer.parseInt(button5.getText()); if (x5==1) { if (h<9) { h= h+1; String string5 = String.valueOf(h); button5.setText(string5); y5= y5+1; } if (y5==8) { x5=0; y5=0; } } else { if (h>0) { h= h-1; String string5 = String.valueOf(h); button5.setText(string5); y5= y5+1; } if (y5==8) { x5=1; y5=0; } } } }); } private void addButtonListener6(JButton B)/>/> { b.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent ae) { eingabe(ae.getActionCommand()); int h = Integer.parseInt(button6.getText()); if (x6==1) { if (h<9) { h= h+1; String string6 = String.valueOf(h); button6.setText(string6); y6= y6+1; } if (y6==8) { x6=0; y6=0; } } else { if (h>0) { h= h-1; String string6 = String.valueOf(h); button6.setText(string6); y6= y6+1; } if (y6==8) { x6=1; y6=0; } } } }); } private void addButtonListener7(JButton B)/>/> { b.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent ae) { eingabe(ae.getActionCommand()); int h = Integer.parseInt(button7.getText()); if (x7==1) { if (h<9) { h= h+1; String string7 = String.valueOf(h); button7.setText(string7); y7= y7+1; } if (y7==8) { x7=0; y7=0; } } else { if (h>0) { h= h-1; String string7 = String.valueOf(h); button7.setText(string7); y7= y7+1; } if (y7==8) { x7=1; y7=0; } } } }); } private void addButtonListener8(JButton B)/>/> { b.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent ae) { eingabe(ae.getActionCommand()); int h = Integer.parseInt(button8.getText()); if (x8==1) { if (h<9) { h= h+1; String string8 = String.valueOf(h); button8.setText(string8); y8= y8+1; } if (y8==8) { x8=0; y8=0; } } else { if (h>0) { h= h-1; String string8 = String.valueOf(h); button8.setText(string8); y8= y8+1; } if (y8==8) { x8=1; y8=0; } } } }); } private void addButtonListener9(JButton B)/>/> { b.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent ae) { eingabe(ae.getActionCommand()); int h = Integer.parseInt(button9.getText()); if (x9==1) { if (h<9) { h= h+1; String string9 = String.valueOf(h); button9.setText(string9); y9= y9+1; } if (y9==8) { x9=0; y9=0; } } else { if (h>0) { h= h-1; String string9 = String.valueOf(h); button9.setText(string9); y9= y9+1; } if (y9==8) { x9=1; y9=0; } } } }); } private void addButtonListenerPruefen(JButton B)/>/> { b.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent ae) { eingabe(ae.getActionCommand()); if ((string == "1") && (string2 == "2") || (string2 == "3") || string2 == "4" || string2 == "5" || string2 == "6" || string2 == "7" || string2 == "8" || string2 == "9") { button1.setBackground(Color.GREEN); anzeige.setText("Richtig"); } } }); } private void eingabe(String a) { anzeige.setText("Prüfen"); } }