Top Java Interview Question on Core Java

image source in Google search

                      This post totally I am concentrate on mostly frequently asked question on core java. Most of the java peoples know these kind of question but how you’re presented at time of interview our goal is to tell you strongly at presence of interview. I think your all very much strong please see and tell me your faced interview also thanks for advanced thanks every one. Now see the following interview question.

Q) What are the difference between Overloading and Overriding in Java?

R) 

Property	Overloading	Overriding
1) Method names	Same	Same
2) Arguments	Different(at least order)	Same(including order)
3) signature	Different	Same
4) return type	No rule or no restriction	Must be same until 1.4 version. But from 1.5 version onwards co-variant return types are allowed
5) throws clause	No restrictions	The size of the checked exception should not be increased. But no restrictions for unchecked exceptions.
6) Access Modifier	No restrictions	Should be decreased
7) Private/final/static	Can’t be overloaded	Can’t be overridden
8) Method resolution	Method resolution takes care by compiler based on reference type and arguments	Takes care by JVM based on runtime object
9) Other names	Compile time (or) static polymorphism (or) early binding	Runtime (or) dynamic polymorphism (or) late binding

Q) What is the difference between StringBuffer and String Builder in Java?

R)

StringBuffer	String Builder
1.All methods are Synchronized	1. No method is synchronized
2. StringBuffer is thread safe	2. StringBuilder is not thread safe
3. Performance is very low	3. Performance is high
4. Available from 1.0 version	4. Available only in 1.5 version

Q) What is the difference between == and .equals() ?

R)

==	.equals()
1) It is an operator and applicable for both primitive and Object references.	1) It is a method applicable for Only Object reference.
2) For Object reference r1, r2 r1 == r2 is true iff both r1 and r2 pointing to the same object on the heap i.e it is meant for reference comparison.	2) Default implementation available in Object class is meant for reference comparison only i.e r1.equals(r2) is true iff both r1,r2 are pointing to the same object on the heap.
3) We can’t override == operator.	3) We can override equals() for content comparison.
4) IF r1 & r2 are incompatible then r1 == r2 results Compile Time Error.	4) If r1 & r2 are incompatible then r1.equals(r2) is always false.
5) For any Object reference r, r == null returns false.	5) For any Object reference r, r.equals(null) returns false.

Q) What is the difference between all cursors in Collection Frame work?

R)

Properties	Enumeration	Iterator	ListIterator
1) It is Legacy?	Yes	No	No
2) It is applicable	Only for legacy classes	For any collection	Only for list implemented classes
3) How to get?	By using elements()	By Using iterator()	By using listIterator()
4) Accessibility	Only read	read & remove	read/remove/replace/add
5) Movement	Single direction (Only Forward)	Single direction (Only Forward)	Biderctional
6) Methods	hasMoreElements() nextElements()	hasNext() next() remove()	hasNext() hasPrevious() .
7) version	1.0	1.2	1.2