A constructor in Java is a special method that is used to initialize objects.
2. How is a constructor in Java identified?
a) It has the same name as the class and a return type
b) It has a different name from the class and no return type
c) It has the same name as the class and no return type
d) It is marked with the 'constructor' keyword
Answer:
c) It has the same name as the class and no return type
Explanation:
Constructors are special methods that have the same name as the class and do not have a return type.
3. Can a Java class have more than one constructor?
a) Yes, it's called constructor overloading
b) No, it can only have one constructor
c) Yes, but they must have the same parameters
d) No, constructors are static and unique
Answer:
a) Yes, it's called constructor overloading
Explanation:
A Java class can have more than one constructor with different parameter lists, known as constructor overloading.
4. What happens if no constructor is defined in a Java class?
a) The class cannot create objects
b) A default constructor is provided by the Java compiler
c) An error occurs during compilation
d) The class uses the constructor of its superclass
Answer:
b) A default constructor is provided by the Java compiler
Explanation:
If no constructor is explicitly defined in a Java class, the Java compiler automatically provides a default constructor.
5. What is a default constructor in Java?
a) A constructor provided by the user without parameters
b) A constructor that sets all object properties to default values
c) A constructor automatically provided by Java with no parameters
d) The first constructor in a class
Answer:
c) A constructor automatically provided by Java with no parameters
Explanation:
A default constructor in Java is a no-argument constructor automatically provided by the compiler if no constructors are explicitly defined in the class.
6. What is the purpose of a parameterized constructor in Java?
a) To initialize objects with different methods
b) To initialize objects with specific values
c) To define static initializations
d) To overload the main method
Answer:
b) To initialize objects with specific values
Explanation:
A parameterized constructor allows initializing objects with specific values provided as parameters at the time of object creation.
7. Can a constructor be private in Java?
a) Yes, for singleton class pattern
b) No, constructors must always be public
c) Yes, but only in abstract classes
d) No, constructors cannot have access modifiers
Answer:
a) Yes, for singleton class pattern
Explanation:
Private constructors can be used in Java, commonly in the singleton pattern, where only one instance of a class is allowed.
8. How do you call a superclass constructor in Java?
a) super()
b) this()
c) superClass()
d) extend()
Answer:
a) super()
Explanation:
The 'super()' keyword is used to explicitly call a superclass constructor from a subclass constructor.
9. What is constructor chaining in Java?
a) Calling one constructor from another within the same class
b) Creating multiple constructors with the same name
c) Connecting two different classes through their constructors
d) A sequence of constructors calling each other in different classes
Answer:
a) Calling one constructor from another within the same class
Explanation:
Constructor chaining refers to a scenario in Java where one constructor calls another constructor in the same class using 'this()'.
10. Which of these is not a feature of constructors in Java?
a) They can return values
b) They have the same name as the class
c) They do not have a return type
d) They are used to initialize objects
Answer:
a) They can return values
Explanation:
Constructors in Java do not return any value, not even 'void'.
11. What is the use of the 'this' keyword in constructors?
a) To call another constructor in the same class
b) To refer to the current class instance
c) To call a method in the same class
d) Both a and b
Answer:
d) Both a and b
Explanation:
The 'this' keyword is used in constructors to call another constructor in the same class and to refer to the current class instance.
12. What differentiates constructors from regular methods in Java?
a) Constructors cannot be called directly
b) Constructors have a return type
c) Constructors cannot have parameters
d) Constructors are named after the class
Answer:
d) Constructors are named after the class
Explanation:
The key difference is that constructors have the same name as the class they are in and are used to initialize objects of that class. Unlike methods, they do not have a return type, not even void.