null pointer exception by Integer

[Tuna Töre]

package smalltesting;
class Parser extends Utils {
public static void main(String [] args) {
System.out.print(new Parser().getInt("42"));
}
int getInt(String arg) {
return Integer.getInteger(arg);
}
}
class Utils {
int getInt(String arg) throws Exception { return 42; }
}

I took this code from SUN's assessment exam and modified it a little

return Integer.getInteger(arg); I want to ask why this line gives null pointer exception ?

[Jesper de Jong]

Do you know what the method Integer.getInteger() does? It most likely does not do what you think it does.

The API documentation says:

Determines the integer value of the system property with the specified name.

If there is no system property named "42", then Integer.getInteger() returns null, and because Parser.getInt() returns a primitive int, the JVM is trying to auto-unwrap null to an int - which causes a NullPointerException.

It's a trick question...

[Harvinder Thakur]

If you check the use of getInteger() method then you would get an answer to your question.
Looking at the code it seems you are better off using valueOf() or parseInt() method of Integer class.

[Tuna Töre]

yeass

very tricky, actually question is not like that I have modified it and see the null pointer exceltion, thanks I got it

package smalltesting;
class Parser extends Utils {
public static void main(String [] args) {
System.out.print(new Parser().getInt("42"));
}
int getInt(String arg) {
return Integer.parseInt(arg);
}
}
class Utils {
int getInt(String arg) throws Exception { return 42; }
}

The real question is like above and works fine