Question "Declare long arrays" in MasterExam downloadable free with purchase of S&B

[Dave Alkire]

Something went totally wrong with this question, "What is the result?". You can see that this compiles fine despite their claim, but instead there's a runtime exception:

 
/*
 * Created on Mar 19, 2005
 *
 */
package practiceExamQuestions.arrayDeclaration;
 
/**
 * Exam II, "Declare long arrays": Again the LearnKey answer is wrong.
 * They say the correct answer is "Compilation error at line 6", which is where
 * we do <code>a1 = a2;</code> But no as you can see and as I answered, it's 
 * a runtime error in the println statement.  
 * 
 * @author David Alkire
 */
public class Test {
 
    public static void main(String[] args) {
        long [][] a1;
        long [] a2 [];
        a2 = new long[3][];
        a1 = a2;
        System.out.println(a1[1][0]);
    }
}

:roll:

[H Singh]

Yes, the answer is wrong.
It will cause a NullPointerException and not a compiler error.

HS

[amit taneja]

error will be due to accessing a[1][0]; ?

becuase thee is no element in the sub-array ?

[Dave Alkire]

becuase thee is no element in the sub-array ?

Yeah, I think it's that the second dimension is declared but not initialized; that is, the compiler doesn't care because it knows that there's an array of longs, but then the jvm gets confused because it doesn't know how many there are supposed to be; so it's trying to use something that hasn't been fully defined.
[ June 08, 2005: Message edited by: Dave Alkire ]