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Java

Posted by AJ Longstreet
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AJ Longstreet
Treehouse Project Reviewer

NullPointerException

Hey Guys, I'm not sure why I can't this the prompter working. I'm hoping you fine folks have some insight for me.

console.readLine() throws a NullPointerException.

package project1;

import java.io.Console;
import java.io.IOException;

class Prompter {

    private static Console console = System.console();
    private static String mPrompt;

    static String prompt(String arg) throws IOException {
        System.out.println(arg);
        mPrompt = console.readLine();
        return mPrompt;
    }

}

3 Answers

Craig Garner
Craig Garner
25,732 Points

If you are running from an IDE, you may not have a console. Look at Scanner instead.

Craig Garner
Craig Garner
25,732 Points

This is from StackOverflow

You can always use System.in and System.out instead, as follows:

String qq;
Scanner scanner = new Scanner(System.in);
qq = scanner.nextLine();
System.out.println(qq);
AJ Longstreet
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.a{fill-rule:evenodd;}techdegree seal-36
AJ Longstreet
Treehouse Project Reviewer
AJ Longstreet
.a{fill-rule:evenodd;}techdegree seal-36
AJ Longstreet
Treehouse Project Reviewer

Thanks, I will look into that. I'm using IntelliJ.

Craig Garner
Craig Garner
25,732 Points

added code example

David Remington
David Remington
18,326 Points
David Remington
David Remington
18,326 Points

It's hard to tell without a little more context, but it looks like you want to prompt the user and then wait and read their input on the command line.

If that's the case, you'll need to use

System.out.print(arg);

instead of

System.out.println(arg);

The println method moves the cursor to the next line which will cause your console.readLine() to fire immediately instead of waiting. This could cause a NullPointerException.

David Remington
David Remington
18,326 Points

This should also work in IntelliJ's console. I ran into it a lot when I was refactoring the KarokeMachine in the IDE course.