#Java: Part 6-Core Java Interview Questions and Answers (Wrapper classes, Static variables, methods and imports)

> >  Part 5-Core Java Interview Questions and Answers (Clone and Immutability)

What are Wrapper classes?
A wrapper class wraps (encloses) around a data type and gives it an object appearance. They include methods to unwrap the object and give back the data type. e.g
int intCount = 100;
Integer wrapperIntCount = new Integer(intCount); //this is called Boxing
int intCountBack = wrapperIntCount.intValue(); //thats unBoxing

There are mainly two uses with wrapper classes:
1) To convert simple data types into objects, i.e to give object form to a data type.
2) To convert strings into data types (known as parsing operations), here methods of type parseXXX() are used.

#Java: Part 5-Core Java Interview Questions and Answers (Clone and Immutability)

> > Part 4-Core Java Interview Questions and Answers (HashCode & equals())

What is a Cloneable interface and what all methods does it contain?
Cloneable is a declaration that the class implementing it allows cloning or bitwise copy of it's object state. It is not having any method because it is a Marker interface.

How clone method works in Java?
The clone() method from java.lang.Object class is used to create a copy of an Object in Java. This copy is known as a clone of original instance. Constructor is not called during cloning of Object in Java.

clone() method is declared as protected and native in Object class. Since its convention to return clone() of an object by calling super.clone() method, any cloning process eventually reaches to java.lang.Object clone() method.

#Java: Part 4-Core Java Interview Questions and Answers (HashCode & equals())

> > Part 3-Core Java Interview Questions and Answers

When you are writing equals() method, which other method or methods you need to override? 
The right answer is hashCode(). Since equals and hashCode has there contract, so overriding one and not other, will break contract between them. Interviewer may ask about what are those contracts, what happens if those contracts breaks etc.