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Java

Posted by Karan Keelor
Karan Keelor
436 Points

Running program in Eclipse..getting nullpointerException error..please help

import java.io.Console;

public class TreeStory {

public static void main(String[] args) {
    Console console = System.console();

      String ageAsString = console.readLine("How old are you? \n" );
    int age = Integer.parseInt(ageAsString);
      if (age < 13) {
        //Insert exit code for if statement
    console.printf("Sorry you must be atleast 13 to use this program\n");
      }
       System.exit(0); 

        String name = console.readLine("Enter a name:  ");
    String adjective = console.readLine("Enter an adjective:  ");
  String noun = console.readLine("Enter a noun: ");
  String adverb = console.readLine("Enter an adverb:  ");
  String verb = console.readLine("Enter a verb:  ");

  console.printf("Your Tree Story: \n------------\n");
  console.printf("%s is a %s %s", name, adjective, noun);
  console.printf("They are always %s %s.\n" ,adverb, verb     );

}

}

Karan Keelor
Karan Keelor
436 Points

Im trying to run it in Eclipse..but getting this error each time:

Exception in thread "main" java.lang.NullPointerException at TreeStory.main(TreeStory.java:8)

Alexandru Doru Grosu
Alexandru Doru Grosu
2,753 Points
Alexandru Doru Grosu
Alexandru Doru Grosu
2,753 Points

Ah okay, that makes sense.

This a bug with Eclipse console, not your program. System.console() returns null sometimes in Eclipse.

https://bugs.eclipse.org/bugs/show_bug.cgi?id=122429

So when you try to do this

String ageAsString = console.readLine("How old are you? \n" );

The console object is null, which is way you get a NullPointerException.

If you want to read input through the console provided by Eclipse I suggest you use java.util.Scanner.

You can find the documentation for it here: http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html

1 Answer

Alexandru Doru Grosu
Alexandru Doru Grosu
2,753 Points
Alexandru Doru Grosu
Alexandru Doru Grosu
2,753 Points

Apologies for the delayed response.

Where exactly are you running this example? In the workspace or in one of the challenges? I am asking because I think the culprit might be again 

Console console = System.console();

As I told you in an earlier post, whenever you write code that uses the console object, you should just assume it was already assigned for you and just use it.

Also, in the javadoc for the Console class it is specified that "Unless otherwise specified, passing a null argument to any method in this class will cause a NullPointerException to be thrown."

So, if in any of the lines that assign input via readLine, assign a null value to the string, you will get a NullPointerException when you try to printf.

In the same javadoc it is also mentioned that "The console-read methods return null when the end of the console input stream is reached, for example by typing control-D on Unix or control-Z on Windows. Subsequent read operations will succeed if additional characters are later entered on the console's input device.".

So your code might not be wrong, you just may be passing wrong arguments without realizing it. Make sure you type in at least one character for all the values you prompt for when you run the code.