Solved

NullPointerException .......

Posted on 2004-09-29
3
191 Views
Last Modified: 2010-03-31
Hi experts,

   I got  a java.lang.NullPointerException at line 00 while I tried to set size for a JButton .... does any one know what i might have missed .... thanks.

--------------------
       :
       :
 getContentPane().setLayout(null);
        getContentPane().setSize(600,600) ;
        getContentPane().setLocation(0,0) ;
        getContentPane().add(myHead) ;
          // set cookies location
        JButton cookies[] = new JButton[10] ;
        for(int i=0; i< cookiesNum; i++){
              int cookies_x, cookies_y ;
             
              cookies_x = ((int)Math.floor(Math.random()*1000)) % 500 ;
              cookies_y = ((int)Math.floor(Math.random()*1000)) % 500 ;
              cookies[i].setSize(20,20) ;                                       // line 00
              cookies[i].setLocation(cookies_x,cookies_y) ;
             
              getContentPane().add(cookies[i]) ;
             
          }
0
Comment
Question by:meow00
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
3 Comments
 
LVL 1

Expert Comment

by:Dave_Toland
ID: 12185912
the array is empty.  try somthing like..

JButton cookies[] = new JButton[10] ;
cookies[0] = new JButton("A Button");
cookies[1] = new JButton("B Button");
cookies[2] = new JButton("C Button");
cookies[3] = new JButton("D Button");

        for(int i=0; i< cookiesNum; i++){
              int cookies_x, cookies_y ;
             
              cookies_x = ((int)Math.floor(Math.random()*1000)) % 500 ;
              cookies_y = ((int)Math.floor(Math.random()*1000)) % 500 ;
              cookies[i].setSize(20,20) ;                                       // line 00
              cookies[i].setLocation(cookies_x,cookies_y) ;
             
              getContentPane().add(cookies[i]) ;
             
          }
0
 
LVL 1

Accepted Solution

by:
Dave_Toland earned 250 total points
ID: 12185940
actually, if you're array is of size 10 you either need to fill it with objects, set empty cells to null or detect the fact that the cell is empty:

the array is empty.  try somthing like..

JButton cookies[] = new JButton[10] ;
cookies[0] = new JButton("A Button");
cookies[1] = new JButton("B Button");
cookies[2] = new JButton("C Button");
cookies[3] = new JButton("D Button");

   //use a dynamic parameter in the for loop
        for(int i=0; i< cookies.length; i++){
              int cookies_x, cookies_y ;
             
              if(cookies[i] != null){

                      cookies_x = ((int)Math.floor(Math.random()*1000)) % 500 ;
                      cookies_y = ((int)Math.floor(Math.random()*1000)) % 500 ;
                      cookies[i].setSize(20,20) ;                                       // line 00
                      cookies[i].setLocation(cookies_x,cookies_y) ;
             
                      getContentPane().add(cookies[i]) ;
              }
          }
0
 
LVL 3

Assisted Solution

by:CI-Ia0s
CI-Ia0s earned 50 total points
ID: 12186166
Except that if you the array to be set up for all 10 values use a for loop. ;)

In fact, you could even put the object creation in your existing loop:

        for(int i=0; i< cookies.length; i++){
              int cookies_x, cookies_y ;
             
              JButton cookies[i] = new JButton("Click me!"); //This is the new line...

              if(cookies[i] != null){

                      cookies_x = ((int)Math.floor(Math.random()*1000)) % 500 ;
                      cookies_y = ((int)Math.floor(Math.random()*1000)) % 500 ;
                      cookies[i].setSize(20,20) ;                                       // line 00
                      cookies[i].setLocation(cookies_x,cookies_y) ;
             
                      getContentPane().add(cookies[i]) ;
              }
          }
0

Featured Post

Independent Software Vendors: We Want Your Opinion

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
How  can  i  resolve  HTTP Status 404 -? 8 78
Which non-HTML GUI front end to use with Java? 3 65
maven disable workspace resolution 1 72
java imports not found 4 70
Java had always been an easily readable and understandable language.  Some relatively recent changes in the language seem to be changing this pretty fast, and anyone that had not seen any Java code for the last 5 years will possibly have issues unde…
Are you developing a Java application and want to create Excel Spreadsheets? You have come to the right place, this article will describe how you can create Excel Spreadsheets from a Java Application. For the purposes of this article, I will be u…
Viewers learn about the “for” loop and how it works in Java. By comparing it to the while loop learned before, viewers can make the transition easily. You will learn about the formatting of the for loop as we write a program that prints even numbers…
Viewers will learn how to properly install Eclipse with the necessary JDK, and will take a look at an introductory Java program. Download Eclipse installation zip file: Extract files from zip file: Download and install JDK 8: Open Eclipse and …
Suggested Courses

737 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question