null pointer exeption : how solve it ?

Code:

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String[] lines = new String[10];
String s ;

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program stop at here

Code:

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if (lines[i].isEmpty() == false){

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and sometimes at

Code:

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if (s.isEmpty()==false){

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with null pointer exeption

i test s!=null and i test
"".equles(s)

but again i get this exeption
i read lines[i] from file

The variables you are using have not been given values. There value is null. The value needs to be an object.
You need to assign them non null values.
s = "A String";

lines[0] = "Another String";

Quote:

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Originally Posted by Norm

The variables you are using have not been given values. There value is null. The value needs to be an object.
You need to assign them non null values.
s = "A String";

lines[0] = "Another String";

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but i get value from file
and it good work but at end i get exeption
i cant manually set value of theme thay get value from file

norm you are exaillent . i never see in any forum so rapidly one persin answer
thank you

Quote:

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but at end i get exeption

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You must have missed giving a variable a good value.
When you get an exception, please copy and paste here the full text of the error message.

Code:

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        if (t1.getText().equals("") ){                       
                                          JOptionPane.showMessageDialog(null ,"etelat ra por konid");
                                      }
                                      else{
                                              lines = mof.getString("book.txt",t1.getText())        ;
                                                if (lines.equals("")){                       
                                                JOptionPane.showMessageDialog(null ,"In Ketab Vojod Nadarad .");         
                                              }
                                              else{
                                                      sb1.append("\nList Of Book in Library With Like This Name Is: \n");  System.out.println(sb1.toString());
                                                      sb2.append("\nBut This  Book Are In Amanat: \n");System.out.println(sb2.toString());
                                                      for(int i = 0 ; i<lines.length;i++){       
                                                      System.out.println("\n000\n");
                                                              if (lines[i].isEmpty() == false){
                                                                      System.out.println(lines[i]+"---------");
                                                                String[] values = lines[i].split(","); 
                                                                s  = values[0];
                                                                System.out.println(s+"++++++");
                                                                sb1.append("\n"+lines[i]+"\n");       
                                                               
                                                                s = mof.findLine("amanat.txt", s);
                                                                System.out.println(s+"+++***+++");
                                                                System.out.println(s);
                                                        }
                                                        System.out.println("-////////////-");
                                                        if (s.isEmpty()==false){       
                                                                System.out.println(s);
                                                                sb2.append("\n"+lines[i]+"\n");

                                                        }
                                                       
                                                      }

                                                      JOptionPane.showMessageDialog(null ,sb3.append(sb1.toString()).append(sb2.toString()).toString());

                                              }

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and this is my file content
1,java2EE,man
2,java2Ee,You
12,java,ali,hich
13,java,ali,hich
14,java,ali,hich

Sorry, can't read the screen print.
To copy the contents of the command prompt window:
Click on Icon in upper left corner
Select Edit
Select 'Select All' - The selection will show
Click in upper left again
Select Edit and click 'Copy'

Paste here.

Are you sure that ALL of the slots in the lines array have good values?
If some could be null you should test them for being null BEFORE testing if they hold an empty String.

Code:

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List Of Book in Library With Like This Name Is:


But This  Book Are In Amanat:


000

1,java2EE,man---------
1++++++
12,12,1390,1390+++***+++
12,12,1390,1390
-////////////-
12,12,1390,1390

000

2,java2Ee,You---------
2++++++
12,12,1390,1390+++***+++
12,12,1390,1390
-////////////-
12,12,1390,1390

000

12,java,ali,hich---------
12++++++
12,12,1390,1390+++***+++
12,12,1390,1390
-////////////-
12,12,1390,1390

000

13,java,ali,hich---------
13++++++
12,12,1390,1390+++***+++
12,12,1390,1390
-////////////-
12,12,1390,1390

000

14,java,ali,hich---------
14++++++
+++***+++

-////////////-

000

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at SearchForm.okButtonEvent(SearchForm.java:94)
        at SearchForm$1.actionPerformed(SearchForm.java:50)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:19
95)

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Quote:

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xception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at SearchForm.okButtonEvent(SearchForm.java:94)

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There is a variable at line 94 that has a value of null when you try to use it to reference a method.
Look at that line and see what variable is null and then back track in your code to see why the variable does not have a good value.

Are you sure that ALL of the slots in the lines array have good values?
If some could be null you should test them for being null BEFORE testing if they hold an empty String.

Quote:

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Originally Posted by Norm

If some could be null you should test them for being null BEFORE testing if they hold an empty String.

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maybee when read from file some value be null
i use
if (lines[i].isEmpty() == false) anf test lines[i].equals("null") but i get exeption
how i check?
how i should to do?
line 94 is : if (lines[i].isEmpty() == false){

You test if a variable is null by using the == operator: if(lines[x] == null ...
The equals method is for comparing the contents of two objects.

Quote:

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Originally Posted by Norm

You test if a variable is null by using the == operator: if(lines[x] == null ...
The equals method if for comparing the contents of two objects.

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thanke youuuuuuuuuuuuu
god help you
it work
this was problem
this one day i search and work to solve it.
how i avoid this problem that waste my time norm how learn like you?