Help with Exception

[bozovilla]

Hi, my code below gives an error:

Exception in thread "main" java.lang.NullPointerException
at Spaceship$DrawA.<init>(Spaceship.java:106)
at Spaceship.<init>(Spaceship.java:147)
at Spaceship.main(Spaceship.java:122)

I am tryingt to create a radar on the west border.


import java.awt.*;
import javax.swing.*;

public class Spaceship extends JFrame implements Runnable{

private JPanel displayP, radarP, rowsP, speedMeterP, messageP;
private JLabel display, radar, rows, speedMeter, message;

Container container;
Thread t;
int i=0;
Font font;


class Flash extends Thread{
private DrawA dA;
private int x;
private int xCor[];
private int yCor[];
private int i;
private int dir;
private Image im;
private Graphics buff;
public Flash(DrawA dA, Image im, Graphics buff){
this.dA = dA;
this.im = im;
this.buff = buff;
xCor = new int[451];
yCor = new int[451];
dir = 10;
}//end of Flash constructor
public void run(){
for(x = 75, i = 0; x <= 525; x++, i++){
xCor[i] = x - 300;
}
for(i = 0; i <= 450; i++){
yCor[i] = (int)Math.sqrt(62500 - (xCor[i] * xCor[i]));
yCor[i] = 300 - yCor[i];
}

for(x = 0; x <= 450; x++){
xCor[x]+=300;
}

i = 0;
while(true){
try{
Thread.sleep(35);
}
catch(Exception e){}


dA.repaint();
i += dir;

if(i < 0 || i > 450){
dir = -dir;
i += dir;
}//end of if
}//end of while
}//end of run
public void draw(Graphics g){
int green = 255;
buff.setColor(Color.black);
buff.fillRect(0, 0, 600, 330);
buff.setColor(new Color(0, 70, 0));
buff.fillArc(50, 50, 500, 500, 25, 130);
buff.setColor(Color.green);
if(i > 450)
return;
if(xCor[i] != 0 && yCor[i] != 0)
buff.drawLine(xCor[i], yCor[i], 300, 300);
if(dir > 0){
for(int j = i; j > (i - 100); j--){
if(j >= 0 && j <= 450){
green -= 2;
buff.setColor(new Color(0, green, 0));
buff.drawLine(xCor[j], yCor[j], 300, 300);
}//end of if
}//end of for
}//end of if
else{
for(int j = i; j < (i + 100); j++){
if(j >= 0 && j <= 450){
green -= 2;
buff.setColor(new Color(0, green, 0));
buff.drawLine(xCor[j], yCor[j], 300, 300);
}// end of if
}//end of for
}//end of else
buff.setColor(Color.green);
buff.drawArc(112, 112, 375, 375, 25, 130);
buff.drawArc(174, 174, 250, 250, 25, 130);
buff.drawArc(238, 238, 125, 125, 25, 130);

buff.drawLine(300, 300, 300, 50);
g.drawImage(im, 0, 0, null);
}//end of draw
}//end of flash class
class DrawA extends Panel{
private Flash fl;
private Image im;
private Graphics buff;
public DrawA(Image im){
this.im = im;
buff = im.getGraphics();
fl = new Flash(this, im, buff);
fl.start();
setBackground(Color.black);
}
public void paint(Graphics g){
fl.draw(g);
}
public void update(Graphics g){
paint(g);
}
}


public static void main(String[] args){

Spaceship f=new Spaceship();
f.setVisible(true);
}//end of main

public DrawA dA;
public Spaceship()
{

setSize(700,500);
setTitle("Spaceship");
setDefaultCloseOperation(EXIT_ON_CLOSE);

font=new Font("TimesNewRoman",font.ITALIC,28);

container = getContentPane();
container.setLayout(new BorderLayout());

displayP=new JPanel();
display = new JLabel("display");
displayP.add(display);
container.add(displayP, BorderLayout.NORTH);

dA = new DrawA(createImage(600, 330));
container.add(dA, BorderLayout.WEST);

rowsP =new JPanel();
rows= new JLabel("rows");
rowsP.add(rows);
container.add(rowsP, BorderLayout.CENTER);

speedMeterP =new JPanel();
speedMeter= new JLabel("speedmeter");
speedMeterP.add(speedMeter);
container.add(speedMeterP, BorderLayout.EAST);

messageP =new JPanel();
message= new JLabel();
messageP.add(message);
container.add(messageP, BorderLayout.SOUTH);//here messageP is added not counter


t=new Thread(this);
t.start();

}//end of constructor

public void run()
{
for(i=25;i>=0;i--)//countdown
{
try
{
Thread.sleep(1000);
message.setText("Estimated Landing Time:"+(Integer.valueOf(i)).toString()+" seconds"); //Here we print the Counter Values
}
catch(Exception e)
{
System.out.println(e);
}
}

repaint();
}//end of run

}

[Fubarable]

One problem is trying to create a graphics object from a JFrame prior to rendering. For example, run this:

import java.awt.Dimension;
import java.awt.Image;

import javax.swing.JFrame;

public class TestCreateImage
{
  private static void createAndShowUI()
  {
    JFrame frame = new JFrame("TestCreateImage");
    frame.setPreferredSize(new Dimension(300, 300));
    Image img = frame.createImage(600, 300);
    System.out.println("Before JFrame rendered, img == null: " + (img == null));
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
    img = frame.createImage(600, 300);
    System.out.println("After JFrame rendered, img == null: " + (img == null));
  }

  public static void main(String[] args)
  {
    java.awt.EventQueue.invokeLater(new Runnable()
    {
      public void run()
      {
        createAndShowUI();
      }
    });
  }
}

[Fubarable]

Cross-posting can frustrate anyone who tries to help you only to find out later that the same answer was given hours ago in a cross-posted thread. No one likes wasting their time, especially a volunteer. The polite thing to do would be to provide links in both cross-posts to each other.