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NullPointerException .......

Posted on 2004-09-29
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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]) ;
             
          }
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Question by:meow00
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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 1000 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 200 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

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