Crack your Java interview by knowing all the questions that your interviewer may ask. Brush up your knowledge with this superb set of Java interview questions & answers prepared by BestOnlineTrainers

1. Java Interview Q & A
By www.bestonlinetrainers.com

2. Q1: To implement key Object in HashMap
which two methods are used?
Answer:
In HashMap, to use any object as Key it must implement equals and
HashCode method in Java.
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3. Q2:What is an immutable object? Mention
an immutable object?
Answer:
Objects that cannot be modified once created are immutable objects in
JAVA. A new object can be resulted due to any modification in an immutable
object. For example, in JAVA, String is immutable. In order to prevent sub class
from overriding methods in Java which can compromise
Immutability, immutable object are mostly final in JAVA. This same functionality
can be achieved by making member as non final but private and not
modifying them except in constructor.
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4. Q3:WState the difference between
creating String as new() and literal?
 Answer:
When string is created with new() Operator, it’s created in a heap and not
added into string pool whereas using literal String are created in String pool
itself which exists in PermGen area of heap, Example: String s = new
String("Test"); It does not put the object in String pool , but needs to be
called String.intern() method which is used to put them into String pool
explicitly. It’s only then that’s it create String object as String literal. For e.g.
String s = "Test" Java automatically put that into String pool

5. Q4:What is difference between StringBuffer
and StringBuilder in Java?
 Answer:
Classic Java questions can seem to be tricky and very easy. In Java
5, StringBuilder is introduced and the only difference between both of them
is that StringBuffer methods are synchronized while StringBuilder is
non- synchronized.

6. Q5: Overriding HashCode() method has any
difference in performance implication?
 Answer:
Yes .A poor HashCode function will result in frequent collision in HashMap
which eventually increase time for adding an object into Hash Map.

7. Q6: While writing stored procedure or accessing
stored procedure from java how is the error
condition handled?
 Answer:
This is one of the tough questions normally asked in Java interview. The
stored procedure should return error code if some operation fails but if
stored procedure itself fails than catching SQLException is the only choice
left .

8. Q7: At the compile time are the imports checked
for validity? That is, will the code containing an
import such as java.lang.ABCD compile up?
 Answer:
Yes. The imports are checked for the semantic validity at the compile time.
The above line of import will not compile if it has the code, an error is shown
saying, cannot resolve symbol.
Symbol: class ABCD
Location: package io
Import java.io.ABCD;

9. Q8: State difference between
Executor.submit() and Executer.execute()
method?
 Answer:
When looking at exception handling, there is a difference. If the tasks
throws an exception and if it was submitted with the execute then this
exception will go to the uncaught exception handler (that is when one
explicitly is not provided, the default one will just print the stack trace to
System.err). If the task is submitted with any thrown exception or a checked
exception or not, is then part of the task's return status. And for a task that
was submitted with submit and that terminates with an exception, the
future.get will re-throw this exception wrapped in an ExecutionException.

10. Q9: What is the difference between factory
and abstract factory pattern?
 Answer:
One more level of abstraction is provided by Abstract Factory .Different
factories from each Abstract Factory responsible for the creation of
different hierarchies of objects based on type of factory are considered.
For example; Abstract Factory extended by
AutomobileFactory, UserFactory, RoleFactoryetc.For every object created
in that genre, each individual factory would be responsible.

11. Q10: Define Singleton? Which is better: to
make whole method synchronized or only
critical section synchronized?
 Answer:
Singleton in JAVA is a class with just one instance in the whole Java
application. One such example is java.lang.Runtime is a Singleton class
.With the introduction Enum by Java 5, creating a Singleton is easy rather
than being tricky as earlier.

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