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Thread: Index error

  1. #1
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    Default Index error

     
    	public static void main(String[] args) throws IOException {
     
    		ArrayList<String> listCliente = new ArrayList<>();
    		ArrayList<String> listCliente1 = new ArrayList<>();
     
    		BufferedReader reader = new BufferedReader(new FileReader("C:\\Users\\java\\Desktop\\prova.txt"));
    		BufferedReader reader1 = new BufferedReader(new FileReader("C:\\Users\\java\\Desktop\\prova1.txt"));
     
    		String line = reader.readLine();
            while(line!=null) {
                System.out.println(line);
                line = reader.readLine();
                listCliente.add(line);
            }
     
     
     
        	String line1 = reader1.readLine();
            while(line1!=null) {
                System.out.println(line1);
                line1 = reader1.readLine();
                listCliente1.add(line1);
            }
     
            System.out.println(listCliente);
            System.out.println(listCliente1);
     
     
     
    		for (int i = 0; i < listCliente.size(); i++) {
    			for (int j = 0; j < listCliente1.size(); j++) {
    				if (listCliente.get(i).equals(listCliente1.get(j))) {
    					System.out.println(listCliente.get(i));
    				}
    			}
    		}
     
    	}
     
    }


    Why do you give me an error?

    output:
    1
    2
    3
    1
    2
    3
    [2, 3, null]
    [2, 3, null]
    2
    3
    Exception in thread "main" java.lang.NullPointerException
    at it.nexid.Test.main(Test.java:41)

    both files have only three strings
    1
    2
    3

  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Index error

    There is a possible logic problem here:
           String line1 = reader1.readLine();    // read first line
            while(line1!=null) {                       //  execute loop if first line not null
                System.out.println(line1);          // print first line
                line1 = reader1.readLine();        // read second line (could be null)
                listCliente1.add(line1);              //  save second line (could be null)
            }
    The code skips saving the first line and saves the null as the last value.
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: Index error

    Grazie

  4. #4
    Super Moderator Norm's Avatar
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    Default Re: Index error

    Prego
    If you don't understand my answer, don't ignore it, ask a question.

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