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Java Interview Questions & Answers

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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 – PowerPoint PPT presentation

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Title: Java Interview Questions & Answers


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
Q2What 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
Q3WState the difference between creating String
as new() and literal?
  • Answer
  • When string is created with new() Operator,
    its 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.
    Its only then thats it create String object as
    String literal. For e.g. String s "Test" Java
    automatically put that into String pool

5
Q4What 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.

12
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