I tried the java.io.Console API using eclipse. My sample code follows.
package app; import java.io.Console; public class MainClass { /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub Console console = System.console(); console.printf("Hello, world!!"); } } When I tried running the example, I got the following error.
Exception in thread "main" java.lang.NullPointerException at app.MainClass.main(MainClass.java:11)
Where did I go wrong? Thanks.
Since you've mentioned in a comment that you're using Eclipse, it appears that there is currently no support for Console in Eclipse, according to this bug report.
The System.console method returns a console associated with the current Java virtual machine, and if there is no console, then it will return null. From the documentation of the System.console method:
Returns the unique
Consoleobject associated with the current Java virtual machine, if any.Returns:
The system console, if any, otherwise
null.
Unfortunately, this the correct behavior. There is no error in your code. The only improvement that can be made is to perform a null check on the Console object to see if something has been returned or not; this will prevent a NullPointerException by trying to use the non-existent Console object.
For example:
Console c = System.console(); if (c == null) { System.out.println("No console available"); } else { // Use the returned Console. } 
System.console returns null if you don't run the application in a console. See this question for suggestions.
System.console returns the unique Console object associated with the current Java virtual machine, if any.
you have to test if console is null before using it.
