I keep getting a NullPointerException when I call the method I created, draw(), in the constructor. It’s especially frustrating because I found a way around it but it’s not what I want. This is the code that works.
public class TutorialGrid extends JFrame{
private JPanel contentPane;
private Graphics g;
private int currentlength;
private int currentwidth;
private Integer[][] maze = new Integer[20][30];
private static TutorialGrid frame;
public static JTable table;
private JTextField title;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
frame = new TutorialGrid();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
public TutorialGrid(){
setResizable(false);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(0, 0, 1366, 768);
contentPane = new JPanel();
contentPane.setBorder(new BevelBorder(BevelBorder.LOWERED, null, null, null, null));
setContentPane(contentPane);
contentPane.setLayout(null);
ImageIcon icon = new ImageIcon("C:\\Users\\Brendan\\Desktop\\GAME\\Images\\BG7.jpg");
input();
table = new JTable();
table.addMouseListener(new MouseAdapter() {
@Override
public void mouseClicked(MouseEvent e) {
draw(maze);
}
});
table.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);
table.setAutoCreateRowSorter(true);
table.setCellSelectionEnabled(true);
table.setColumnSelectionAllowed(true);
table.setDoubleBuffered(true);
table.setDragEnabled(true);
table.setFillsViewportHeight(true);
table.setFocusCycleRoot(true);
table.setFocusTraversalPolicyProvider(true);
table.setIgnoreRepaint(true);
table.setInheritsPopupMenu(true);
table.setSurrendersFocusOnKeystroke(true);
table.setBackground(new Color(0, 0, 0));
table.setForeground(new Color(255, 255, 255));
table.setBorder(new LineBorder(new Color(139, 0, 0)));
table.setBounds(180, 40, 1000, 600);
contentPane.add(table);
title = new JTextField();
title.addMouseListener(new MouseAdapter() {
@Override
public void mouseClicked(MouseEvent e) {
draw(maze);
}
});
title.setHorizontalAlignment(SwingConstants.CENTER);
title.setText("Click to Start");
title.setBorder(new LineBorder(new Color(0, 128, 0)));
title.setEditable(false);
title.setForeground(Color.WHITE);
title.setBackground(new Color(0, 0, 0));
title.setBounds(606, 11, 151, 20);
contentPane.add(title);
title.setColumns(10);
JLabel lblBgpanel = new JLabel("", icon,JLabel.CENTER);
lblBgpanel.setBounds(0, 0, 1360, 740);
contentPane.add(lblBgpanel);
}
As you can see I have mouseListeners on both the table and the title which call the draw method successfully no problems at all. It draws the grid I want on the table, however in order to draw it I have to click one of those containers. I want it to draw the grid when the JFrame is initialized. But if I simply put draw(maze); in the constructor it gives me a null pointer exception. This is the code for both the methods draw and input which are used to draw the grid.
public void draw(Integer[][] maze){
int x= 125;
int y =50;
int width1 =25;
int length1 =25;
g=table.getGraphics();
for(int i=0; i<20; i++)
{
for(int j=0; j<30; j++)
{
if(maze[i][j] == maze[currentlength][currentwidth])
{
g.setColor(Color.YELLOW);
g.fillRect(x,y,width1,length1);
g.setColor(Color.RED);
g.drawRect(x,y,width1,length1);
x = x+25;
}
else if(maze[i][j] == 1)
{
g.setColor(Color.BLACK);
g.fillRect(x,y,width1,length1);
g.setColor(Color.RED);
g.drawRect(x,y,width1,length1);
x = x+25;
}
else if(maze[i][j] == 0)
{
g.setColor(Color.BLUE);
g.fillRect(x,y,width1,length1);
g.setColor(Color.RED);
g.drawRect(x,y,width1,length1);
x = x+25;
}
else if(maze[i][j] == -2)
{
g.setColor(Color.GREEN);
g.fillRect(x,y,width1,length1);
g.setColor(Color.RED);
g.drawRect(x,y,width1,length1);
x = x+25;
}
else if(maze[i][j] == -10)
{
g.setColor(Color.WHITE);
g.fillRect(x,y,width1,length1);
g.setColor(Color.RED);
g.drawRect(x,y,width1,length1);
x = x+25;
}
}
y=y+25;
x=125;
}
}
public void input(){
//Imports and reads grid file
Scanner scan = null;
try
{
FileReader grid = new FileReader("C:\\Users\\Brendan\\Desktop\\tutorialgrid.txt");
scan = new Scanner(grid);
}
catch(FileNotFoundException e)
{
System.out.println(e.getMessage() + "Could not find that file");
System.exit(0);
}
for(int i=0; i<20; i++)
{
for(int j=0; j<30; j++)
{
maze[i][j]=scan.nextInt();
if(maze[i][j] == -1)
{
currentlength = i;
currentwidth = j;
}
if(maze[i][j] == -10)
{
}
}
}
}
}
All this is inside the same class. This is what I’m trying to do but gives me an error. I add the draw(maze) at the bottom of the constructor and it blows up on me the moment I try to run it.
public TutorialGrid(){
setResizable(false);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(0, 0, 1366, 768);
contentPane = new JPanel();
contentPane.setBorder(new BevelBorder(BevelBorder.LOWERED, null, null, null, null));
setContentPane(contentPane);
contentPane.setLayout(null);
ImageIcon icon = new ImageIcon("C:\\Users\\Brendan\\Desktop\\GAME\\Images\\BG7.jpg");
input();
table = new JTable();
table.addMouseListener(new MouseAdapter() {
@Override
public void mouseClicked(MouseEvent e) {
draw(maze);
}
});
table.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);
table.setAutoCreateRowSorter(true);
table.setCellSelectionEnabled(true);
table.setColumnSelectionAllowed(true);
table.setDoubleBuffered(true);
table.setDragEnabled(true);
table.setFillsViewportHeight(true);
table.setFocusCycleRoot(true);
table.setFocusTraversalPolicyProvider(true);
table.setIgnoreRepaint(true);
table.setInheritsPopupMenu(true);
table.setSurrendersFocusOnKeystroke(true);
table.setBackground(new Color(0, 0, 0));
table.setForeground(new Color(255, 255, 255));
table.setBorder(new LineBorder(new Color(139, 0, 0)));
table.setBounds(180, 40, 1000, 600);
contentPane.add(table);
title = new JTextField();
title.addMouseListener(new MouseAdapter() {
@Override
public void mouseClicked(MouseEvent e) {
draw(maze);
}
});
title.setHorizontalAlignment(SwingConstants.CENTER);
title.setText("Click to Start");
title.setBorder(new LineBorder(new Color(0, 128, 0)));
title.setEditable(false);
title.setForeground(Color.WHITE);
title.setBackground(new Color(0, 0, 0));
title.setBounds(606, 11, 151, 20);
contentPane.add(title);
title.setColumns(10);
JLabel lblBgpanel = new JLabel("", icon,JLabel.CENTER);
lblBgpanel.setBounds(0, 0, 1360, 740);
contentPane.add(lblBgpanel);
draw(maze);
}
Here’s the error.
java.lang.NullPointerException
at game.TutorialGrid.draw(TutorialGrid.java:136)
at game.TutorialGrid.<init>(TutorialGrid.java:111)
at game.TutorialGrid$1.run(TutorialGrid.java:41)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)
The game.TutorialGrid.draw line 136 is the line where the draw method starts.
The game.TutorialGrid. line 111 is last line in the constructor where I put draw(maze).
The game.TutorialGrid$1.run line 41 is the line frame = new TutorialGrid();
Help is appreciated.
getGraphics() returns null until things are visible.