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  • Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 196
  • Last Modified:

NullPointerException .......

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
meow00
Asked:
meow00
  • 2
2 Solutions
 
Dave_TolandCommented:
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
 
Dave_TolandCommented:
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
 
CI-Ia0sCommented:
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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