Java Exam 2025 Questions and Answers

Java Exam 2025 Questions and
Answers


If you overwrite clone(), which 3 rules must this method obey? - ANSWER✔✔-1) the

new object should be new: memory address should differ


2) Both should be an object of the same class


3) Both should be in the same state:


a.clone().equals(a) == true


Why do we need to implement the Clonable interface? - ANSWER✔✔-At runtime it

would throw the CloneNotSupportedException if we don't implement the Cloneable

interface. A class implements the Cloneable interface to indicate to the Object.clone()

method that it is legal for that method to make a field-for-field copy of instances of that

class.


What is a marker interface? - ANSWER✔✔-A Marker interface, has no method.


Serializable, Clonable are marker interfaces.

,How do you clone an object? - ANSWER✔✔-MyClone a = (MyClone) c.clone()


- TypeCast is nessesary.


- handle CloneNotSupportedException


Why can Annotations replace marker interfaces? - ANSWER✔✔-Annotations can

convey metadata about the class to its consumers without creating a separate type for it.

Annotations let you pass information to classes that "consume" it.


What is Double-Checked Locking? - ANSWER✔✔-To reduce the overhead of acquiring

a lock by first testing the locking criterion without actually acquiring the lock.


How do you make an object serializable? - ANSWER✔✔-The class must implement the

java.io.Serializable interface


Java object serialization is performed using which classes? - ANSWER✔✔-Java object

serialization (writing) is done with the ObjectOutputStream and deserialization

(reading) is done with the ObjectInputStream.


What is serialVersionUID? - ANSWER✔✔-In addition to implementing the Serializable

interface, a class intended for serialization should also contain a private static final long

variable named serialVersionUID.

,The serialVersionUID variable is used by Java's object serialization API to determine if a

deserialized object was serialized (written) with the same version of the class, as it is

now attempting to deserialize it into.


If you make changes to the class that affect serialization, you should also change its

serialVersionUID value.


What is escape analysis? - ANSWER✔✔-escape analysis is a method for determining

the dynamic scope of pointers - where in the program a pointer can be accessed.


What is the size of byte? - ANSWER✔✔-8 bits


What is the size of char? - ANSWER✔✔-16 bits


What is the size of short? - ANSWER✔✔-16 bits


What is the size of int? - ANSWER✔✔-32 bits


what is the size of long? - ANSWER✔✔-64 bits


what is the size of float? - ANSWER✔✔-32 bits


what is the size of double? - ANSWER✔✔-64 bits


What is the range of byte - ANSWER✔✔--128 to 127


What is the range of short? - ANSWER✔✔--32,768 to 32,767


What is the range of int? - ANSWER✔✔--2,1 billion to 2,1billion

, How do you check if a number is even? - ANSWER✔✔-check if number AND 1 is 0


How do you test if the n-th bit is set? - ANSWER✔✔-Shift n times to the right and then

AND


How can you set the n-th bit - ANSWER✔✔-Shift n times to the left and OR


How can you unset the nth bit - ANSWER✔✔-Shift n times to the left and invert, then

AND


How can you toggle the nth Bit? - ANSWER✔✔-Shift n times to the left and XOR


How can you turn off the rightmost 1Bit? - ANSWER✔✔-AND with (number - 1)


How can you return only 1 or 0 for the rightmost 1Bit value? - ANSWER✔✔-number &

( - number)


How can you also declare -x bitwise? - ANSWER✔✔-~x + 1


What is ~0 bitwise? - ANSWER✔✔-0


How can you right propagate the rightmost 1-bit? - ANSWER✔✔-number OR (number

- 1), does not work for 0


What is -1 in twos complement? - ANSWER✔✔-1111 1111


How can you isolate the rightmost 0-bit? - ANSWER✔✔-invert number AND (number

+ 1)