Java Interview

1.1 Abstract class ?

• A class which is declared with the abstract keyword
• It can have abstract and non-abstract methods (method with the body).
• Abstraction is a process of hiding the implementation details and showing only functionality to the user.
• There are two ways to achieve abstraction in java (Abstract class & Interface)
• It cannot be instantiated, but can extend
• It can have constructors and static methods also
• It can have final methods which will force the subclass not to change the body of the method.
• Github Code

1.2 Features of Abstract class ?

• Template
• Loose Coupling
• Code reusability
• Abstraction
• Dynamic Resolution

1.3 Interface?

• It is used to achieve abstraction.
• By interface, we can support the functionality of multiple inheritance.
• It can be used to achieve loose coupling.
• Github Code

1.4 Java doesn't support multiple inheritances.Why?

• it can lead to diamond problem.

1.5 Object class methods

• hashCode() - // return memory location of objects
• finalize()
• clone()
• toString() - // return classname@hexadecimal_address

1.6 String immutability

• Every time value changes, new memory loction will allocate and will store it there
• If other variable with same string value created then , it reuse old memory location (memory efficient)
• Thread Safe
• Security

1.7 == and equals

• == - check only object references in memory
• .equals() - does the same as ==, overridden possible . But it string & enum it will do deep comparison

1.8 final and finally

• final
• In primitive can't modify
• In object decl - can't change obj ref.
• In class - can't inherit
• In class method - can't override method in chlid class
• Finally
• try{} catch(){} finally{}