SCJP Sun Certified Java Programmer 4

Question 1

What is autoboxing in Java?

Accepted Answer

Automatic conversion between primitives and their wrapper types

Answer

Autoboxing automatically converts primitives (like int) to their wrapper objects (like Integer) and vice versa.

Question 2

Which of the following is NOT a valid way to create a thread in Java?

Accepted Answer

Implementing Threadable interface

Answer

There is no 'Threadable' interface in Java; threads are created via Thread, Runnable, or Callable.

Question 3

What is the difference between '==' and 'equals()' when comparing String objects?

Accepted Answer

'==' compares references; equals() compares content

Answer

'==' compares object references (memory addresses), while String's equals() compares character content.

Question 4

In Java, which keyword is used to prevent a class from being subclassed?

Accepted Answer

final

Answer

Declaring a class as final prevents it from being extended by any subclass.

Question 5

What is the output of: System.out.println(Math.floor(-2.5));

Accepted Answer

-3.0

Answer

Math.floor() returns the largest integer less than or equal to the argument, so floor(-2.5) = -3.0.

SCJP - Sun Certified Java Programmer Practice Test