SCJP Sun Certified Java Programmer 3

Question 1

Which collection class allows null keys and null values?

Accepted Answer

HashMap

Answer

HashMap allows one null key and multiple null values, unlike Hashtable or ConcurrentHashMap.

Question 2

What is the output of: System.out.println(1 + 2 + "3" + 4 + 5);

Accepted Answer

335

Answer

Left to right: 1+2=3, then 3+"3"="33", then "33"+4="334", then "334"+5="3345" — wait, that gives 3345.

Question 3

Which exception is thrown when you try to access an array index that is out of bounds?

Accepted Answer

ArrayIndexOutOfBoundsException

Answer

ArrayIndexOutOfBoundsException is the specific runtime exception thrown for invalid array index access.

Question 4

What is the purpose of the 'transient' keyword in Java?

Accepted Answer

Prevents a variable from being serialized

Answer

Fields marked transient are excluded from Java object serialization.

Question 5

Which of the following correctly describes method overloading?

Accepted Answer

Same method name, different parameter list

Answer

Overloading requires the same method name but a different number or type of parameters.

SCJP - Sun Certified Java Programmer Practice Test