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Question 1

What do access level modifiers determine?

Answer 1

They determine whether other classes can use a particular field or invoke a particular method.

Question 2

What does the public access modifier do?

Answer 2

Members are accessible by everyone.

Question 3

What does the private access modifier do?

Answer 3

Members are only accessible from within the class.

Question 4

What does the protected access modifier do?

Answer 4

Accessible from within the class, within its subclasses, and within classes from the same package.

Question 5

What is the default access level if no modifier is stated?

Answer 5

Package-private level access.

Question 6

What does the final keyword do when declaring a variable?

Answer 6

Prevents its value from being changed.

Question 7

What happens to an object’s reference when declared as final?

Answer 7

The variable cannot be made to refer to a different object after the declaration.

Question 8

What happens to the state of an object declared as final?

Answer 8

The state of the object can change.

Question 9

What is the effect of a final method?

Answer 9

It cannot be overridden.

Question 10

What is the effect of a final class?

Answer 10

It cannot be extended.

Question 11

What is a static field?

Answer 11

A field that belongs to the class instead of each instance having its own.

Question 12

How do you access a static field or method?

Answer 12

Use the class name.

Question 13

What do static and final combined create?

Answer 13

A constant.

Question 14

What can interfaces specify?

Answer 14

A list of required methods to be implemented.

Question 15

What does decoupling mean in the context of interfaces?

Answer 15

Separation of the interface from the implementation.

Question 16

Why use interfaces?

Answer 16

Enable and enforce strict sharing of methods among classes and make code more reusable.

Question 17

What can an interface contain?

Answer 17

Method signatures, default methods, static methods, and nested types.

Question 18

What is the difference between class inheritance and interface inheritance?

Answer 18

Class inheritance uses ‘extends’ while interface inheritance uses ‘implements’.

Question 19

What is one of the main characteristics of an interface?

Answer 19

It cannot have a constructor or any instance fields.

Question 20

What is an abstract class?

Answer 20

A cross between a regular class and an interface.

Question 21

What must any abstract method use?

Answer 21

The abstract keyword.

Question 22

Can an abstract class be instantiated?

Answer 22

No, it cannot be instantiated even if it has a constructor.

Question 23

When should you consider using abstract classes?

Answer 23

When code needs to be shared among closely related classes.

Question 24

When should you consider using interfaces?

Answer 24

When unrelated classes would implement the interface.

Question 25

What is an inner class?

Answer 25

A member of the outer class.

Question 26

What access does an inner class have?

Answer 26

Direct access to the outer class's members, including private ones.

Question 27

Why create inner classes?

Answer 27

To logically group classes that are only used in one place.

Question 28

What are the two special kinds of inner classes?

Answer 28

Local Class and Anonymous Class.

Question 29

What is a local class?

Answer 29

An inner class declared inside a block.

Question 30

What is an anonymous class?

Answer 30

A class with no name that is declared and instantiated in one statement.

Question 31

What are the differences between local and anonymous classes?

Answer 31

* Local has a name * Local can have multiple instances * Local can have a constructor * Local can implement multiple interfaces * Anonymous cannot.

Question 32

What is meant by effectively final?

Answer 32

A variable not declared as final, but its value does not change anywhere else in the code.

Question 33

What are modifiers in Java?

Answer 33

Modifiers are keywords in Java that define the properties of classes, methods, and variables.

Question 34

True or False: The 'private' modifier allows access to a class member only within its own class.

Answer 34

True

Question 35

What does the 'public' modifier indicate?

Answer 35

The 'public' modifier indicates that a class member is accessible from any other class.

Question 36

Fill in the blank: The ______ modifier restricts access to the package and subclasses.

Answer 36

protected

Question 37

What is an abstract class?

Answer 37

An abstract class is a class that cannot be instantiated and may contain abstract methods that must be implemented by subclasses.

Question 38

How do you declare an abstract method in Java?

Answer 38

By using the 'abstract' keyword in a method declaration within an abstract class.

Question 39

True or False: An interface can contain method implementations.

Answer 39

False

Question 40

What is the main purpose of an interface in Java?

Answer 40

An interface defines a contract that classes can implement, specifying methods that must be provided.

Question 41

Multiple Choice: Which keyword is used to implement an interface in a class? A) extends B) implements C) inherits

Answer 41

B) implements

Question 42

What is the difference between an interface and an abstract class?

Answer 42

An interface cannot contain any implementation, whereas an abstract class can have both abstract and concrete methods.

Question 43

What is an inner class?

Answer 43

An inner class is a class defined within another class and has access to the outer class's members.

Question 44

True or False: Anonymous classes can be used to instantiate a class without giving it a name.

Answer 44

True

Question 45

What is the syntax to create an anonymous class?

Answer 45

By using the 'new' keyword followed by the class or interface name and overriding its methods.

Question 46

Fill in the blank: An ______ class is declared inside another class and can access the outer class's members.

Answer 46

inner

Question 47

What keyword is used to define an abstract class?

Answer 47

abstract

Question 48

Multiple Choice: Which of the following can be declared as abstract? A) Class B) Method C) Both A and B

Answer 48

C) Both A and B

Question 49

What happens if a class extends an abstract class?

Answer 49

It must implement all abstract methods of the parent abstract class unless it is also declared abstract.

Question 50

True or False: An interface can extend another interface.

Answer 50

True

Question 51

What is a static nested class?

Answer 51

A static nested class is a nested class that does not have access to instance variables and methods of the outer class.

Question 52

Fill in the blank: The keyword ______ is used to declare a class that cannot be subclassed.

Answer 52

final

Question 53

What is the default access modifier for class members in Java?

Answer 53

Package-private (no modifier specified)

Question 54

Multiple Choice: Which modifier makes a class member accessible only within its own package? A) private B) protected C) default

Answer 54

C) default

Question 55

What type of class cannot be instantiated directly?

Answer 55

Abstract class

Question 56

True or False: You can create an instance of an abstract class.

Answer 56

False

Question 57

What is the use of the 'synchronized' modifier?

Answer 57

The 'synchronized' modifier is used to control access to a method or block by multiple threads.

Question 58

Fill in the blank: Inner classes can access the ______ class's members directly.

Answer 58

outer

Question 59

What does it mean if a class is marked as 'final'?

Answer 59

It cannot be subclassed.

Question 60

Multiple Choice: Which of the following is NOT a valid modifier in Java? A) public B) private C) global

Answer 60

C) global

Question 61

What is the benefit of using interfaces?

Answer 61

Interfaces allow for multiple inheritance of type and define a contract for classes to implement.

Question 62

True or False: A class can implement multiple interfaces.

Answer 62

True

Question 63

What is the result of declaring a method as 'abstract'?

Answer 63

The method must be implemented in any concrete subclass.

Question 64

Fill in the blank: A class that contains at least one abstract method is considered ______.

Answer 64

abstract

Question 65

What is the main characteristic of an anonymous class?

Answer 65

It does not have a name and is defined at the point of instantiation.

Question 66

What is the purpose of the 'volatile' modifier?

Answer 66

The 'volatile' modifier indicates that a variable's value will be modified by different threads.

Question 67

True or False: An abstract class can implement an interface.

Answer 67

True

Question 68

What is the result of a class implementing an interface?

Answer 68

The class must provide implementations for all methods declared in the interface.

Question 69

Fill in the blank: Methods in an interface are implicitly ______.

Answer 69

public

Question 70

What is the main purpose of using inner classes?

Answer 70

To logically group classes that are only used in one place and to increase encapsulation.