K&B Page 814 Q7 Regarding Assertions in Java

[Peter Swiss]

Here is the question

import java.util.*;

public class Antique{
  public static void main(String [] args) {
     List<String> myList = new ArrayList<String>();
     assert(args.length > 0);
     }
}

Which sets of commands will compile and run without exception or error?

A. javac Antique.java
java Antique
B. javac Antique.java
java -ea Antique
C. javac -source 6 Antique.java
java Antique
D. javac -source 1.4 Antique.java
java Antique
E. javac -source 1.6 Antique.java
java -ea Antique


Answer says A and C are correct.
A is obvious.
What is the difference between C and D? Since Assertions were added to Java 1.4, options C and D are the same. So even D should be correct.

Please reply.

Thank you.

[Vijay keshava]

D would have been correct, if instead of List<String> myList = new ArrayList<String>(); we had List myList = new ArrayList(); Generics were introduced only in java 1.5. The question is tricky, since you are focusing on assertion, but the catch is with usage of generics

[Peter Swiss]

oh, yes!! LOL that was good!
Thanks Vijay!

[Glen Iris]

Why is B wrong? - I guess assertions are enabled by default but what is wrong with explicitly enabling them too?

Why is E wrong?

[Helen Ma]

Suppose, we are using Java 6 to compile.
B and E will compile, but it will throw the error as there is no argument from the command-Line.
assert (args.length>0) will be false and print an AssertionError message.

[Glen Iris]

thank you helen

[dennis deems]

Glen Iris wrote:Why is B wrong? - I guess assertions are enabled by default but what is wrong with explicitly enabling them too?

Assertions are disabled by default. That's why A works. The line that would cause an AssertionError is ignored unless assertions are explicitly enabled.

[Glen Iris]

Thanks Dennis. I had figured that out in the mean time but its always good to have a solid Java person back up my assumptions.