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)
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)
