Inner and Abstract Classes & Interfaces

Question 1

Java Interface

Answer 1

• a blueprint of a class
• an abstract type that is used to specify behavior(s)/function(s) that all the classes must implement
• it has static constants and abstract methods (not method body)

Question 2

Why do we need a Java Interface?

Answer 2

to overcome the problem of multiple inheritances

Question 3

List interface

Answer 3

• provides a way to store the ordered collection
• it is a child interface of Collection
• it is an ordered collection of objects in which duplicate values can be stored
• since List preserves the insertion order, it allows positional access and insertion of elements

Question 4

Vector

Answer 4

xxx

Question 5

synchronized

Answer 5

xxx

Question 6

What’s wrong with the code below?

List < String > fields = new List < String >;

Answer 6

‘List’ is abstract; cannot be instantiated.

Question 7

Explain codes:

ISaveable werewolf = new Monster (“Werewolf”, 20, 40);
System.out.println (((Monster) werewolf).getStrenth());

Answer 7

xxx

Question 8

How to create an instance of an inner class?

Answer 8

OuterClass.InnerClass reference = outerObject.new InnerClassConstructor()

Gearbox mcLaren = new Gearbox(6);
Gearbox.Gear first = mcLaren.new Gear(1, 12.3);

Question 9

Inner class

Answer 9

it refers to the class that is declared within class or interface

Question 10

Types of Inner Classes

Answer 10

1. Nested/Normal/Regular Inner Class
2. Method Local Inner Class
3. Static Nested Class
4. Anonymous Inner Class

Question 11

Nested/Normal/Regular Inner Class

Answer 11

• when we declare any named class directly inside a class without a static modifier