Interview Questions and Answers for 'Java' | Search Interview Question

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Q631. What are the advantages and disadvantages of using lock classes from java.util.concurrent.locks vs. synchronized methods ?

Core Java

Ans. http://www.devinline.com/2015/10/Lock-Vs-synchronized-in-java.html

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Q632. What will be the output of following code

Integer x = 1;
Integer y = 2;
System.out.println(x == y);

What if you change 1 to "1" and Integer to String?

Core Java

Ans. It will print "true" with integers as well as strings. The reason is "Integer constant pool" and "String pool"

String pool maintains pool of string literals. When a string literal is used for the first time, a new string object is created and is added to the pool. Upon it's subsequent usage , the reference for the same object is returned. Similarly java uses integer constant pool.

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Q633. What are the trade offs between public constructor and static final method ?

Core Java

Ans. Public constructor is simple and easy as it's the default way of object creation. So there are no additional coding overheads as compiler provides the default constructor if none is provided by coder.

With static final methods, it facilitates loose coupling by segregating the responsibility of object creation to a separate method. Validation can be done on the constructor arguments before calling it. Moreover if any adaption on the arguments is required that can achieved easily with factory method.On the flip side, there is coding overhead and additional method call.

Sample Code for constructor

Sample Code for factory

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Q634. How can we get an array out of ArrayList ?

Core Java

Ans. We can get an array out of ArrayList by using toArray() method of an array list.

String a[] = arrayList.toArray();

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Q635. Can we override the overloaded methods too ?

Core Java

Ans. Yes. Both concepts are independent of each other. Overriding depends on the methods with same name and signature whereas Overloading on same name but with different signatures. All definitions of an overloaded method can be individually overridden in the derived class.

For example -

Class A has overloaded methods "public void myMethod(String str)" and "public void myMethod(int x)"

We can have derived class ClassB extends ClassA and hence can override both methods myMethod(String str) and myMethod(int x) in ClassB

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Q636. What is "dynamic method dispatch" in java ?

Core Java

Ans. dynamic method dispatch is a process in which a call to an
overridden method is resolved at runtime rather than at compile-time. This is used to achieve runtime polymorphism in java.

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Q637. What is the difference between Enumeration and Iterator ?

Core Java

Ans. Enumeration can iterate only legacy collections like Vector , HashTable and Stack whereas Iterator can iterate both legacy and non legacy collections.

Enumeration is less safer than Iterator

Enumeration is fail safe whereas Iterator is fail fast

Iterator allows for removal of element while traversal whereas Enumeration doesn't have remove method.

Enumerations were introduced in Java 1 whereas Iterators were introduced with Java 2

Enumerations have methods like hasMoreElements and nextElement whereas Iterators have methods like hasNext, next and remove

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Q638. What is meant Java is "Write Once Run Anywhere" ?

Core Java

Ans. It means that Java is compiled to byte code that is platform independent and hence can be run anywhere or any machine.

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Q639. What does the modularity in project jigsaw means ?

Core Java

Ans. It means that now individual modules will be built independently instead of complete jdk built in a single jar file. So we will have multiple jars instead of single jar. Moreover this organization would result in lighter applications as they can just built themselves with the required jars and hence ignoring the not required and legacy modules.

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Q640. What is project Jigsaw in Java 9 ?

Core Java

Ans. The projects aims to organize the Java source code into independent modules and hence facilitate building them independently.So now we will have multiple core java jars instead of single one. This way of organizing the code would offer following advantages

1. Will make applications lighter as only required modules will be built with the application. Moreover there are some legacy packages currently which anyone hardly use.

2. Reuse same class whole identifiers across different modules.

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Q641. What are the changes in Java 9 ?

Core Java

Ans. JVM and JDK are getting smaller.

New command line tool called jshell that will add native support and popularize a Java way to REPL (Read-Eval-Print-Loop)

private methods in interfaces

Introduction of the module system or project Jigsaw

JavaDoc Search

Light version of JSON API

HTTP2 client

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Q642. If an Abstract class has only abstract methods, What's the difference between such a class and an interface ?

Core Java

Ans. Such a class still can have member elements which can be inherited and hence facilitate code reuse. Moreover Abstract class can have non final static elements whereas interfaces are only allowed to have static final elements.

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Q643. What are some uses of interceptors ?

Java EE

Ans. Authentication / Authorization
URL forwarding
Auditing / Logging
Localization

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Q644. Why is goto not used in Java?

Core Java

Ans. Goto statement results in unstructured jumps in control from one code location to another and hence makes the code very difficult
to read , maintain and debug. Moreover Goto can always be replaced using other statements like break / continue and hence results in structured movement of programming control.

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Q645. Are Annotations better than using XML configs ?

Core Java

Ans. Yes , as both code and its meta information reside in the same file, it promotes better readability and maintenability.

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Q646. What is the use of Annotations in Java ?

Core Java

Ans. Annotations are used to specify meta information about the code.

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Q647. Can we deploy an application to server using a jar file ?

Java EE

Ans. Conventionally we need a WAR file to be deployed to server. Though with Spring Boot we can even deploy using jar.

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Q648. Write a Program to convert a binary to number ?

Core Java

Ans. int convert(int binaryInt) {
int sumValue=0;
int multiple = 1;
while(binaryInt > 0) {
binaryDigit = binaryInt;
binaryInt = binaryInt /10;
sumValue = sumValue (binaryDigit * multiple);
multiple = multiple * 2;
}

return sumValue;
}

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Q649. Write a multi threaded Program that will simulate transferring of money across accounts ?

Core Java

^{This question was recently asked at 'Trustwave'.This question is still unanswered. Can you please provide an answer.}

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Q650. Which component of MVC you like to work on ?

Java EE

^{This question was recently asked at 'CapTech'.This question is still unanswered. Can you please provide an answer.}

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Q651. Write a class and override the equals and hashcode method ?

Core Java

Ans. class Student
{
///
///
///
private int id;
private String name;

///
///
///
public Student(int id, String name)
{
this.name = name;
this.id = id;

}// Student

///
///
///
public int getId()
{
return id;

}// getId

///
///
///
public void setId(int id)
{
this.id = id;

}// setId

///
///
///
public String getName()
{
return name;

}// getName

///
///
///
public void setName(String name)
{
this.name = name;

}// setName

@Override
public boolean equals(Object obj)
{
if (obj == null) return false;
if (!(obj instanceof Student))
return false;
if (obj == this)
return true;

return this.getId() == ((Student) obj).getId();

}// equals

///
///
///
@Override
public int hashCode()
{
return this.getId();

}// hashCode

}// Student

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Q652. How does java identifies which method to be called in method overriding or runtime polymorphism, when both methods share the same name and signature ?

Core Java

Ans. Java identifies the method to be called at runtime by the object that is being referenced.

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Q653. Which of the two - compile time and run time polymorphism - requires signature of the method to be different ?

Core Java

Ans. runtime polymorphism or method overriding doesn't require method name and signature to be different whereas compile time polymorphism or method overloading requires method name to be same but the signature to be different.

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Q654. How can you extract integers from string values and add (sum it up) all the extracted integers? e.g "James34long4island322in3rdAvenue" ---> 34 4 322 3 = 363

Core Java

^{This question was recently asked at 'Horizon Solutions'.This question is still unanswered. Can you please provide an answer.}

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Q655. How is garbage collection in Java 8 different from Java 7 ?

Core Java

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Q656. What is the use of java.util.concurrent package in Java ?

Core Java

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Q657. What is the difference between keywords, identifiers and literals in java ?

Core Java

Ans. Keywords are the reserved words that have a pre defined meaning for the compiler and hence are restricted to be used as identifiers.

Identifiers are the name assigned to different programming constructs like classes, interfaces, methods , variables etc.

Literals are the values that are assigned to Identifiers.

For example

int count = 0;

in the above statement "int" is a keyword, "count" is an identifier and "0" is a literal

Sample Code for keywords

Sample Code for identifiers

Sample Code for literals

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Q658. What are the some literals in java that are reserved and hence cannot be used as identifiers ?

Core Java

Ans. true , false and null

Sample Code for literals

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Q659. Can we use true and false as identifiers in java ? Are they keywords in Java ?

Core Java

Ans. true and false are literals in java. No we cannot use them as identifiers.

Sample Code for literal

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Q660. What is the importance of Abstract Class ?

Core Java

Ans. Abstract classes provide a mechanism of interfacing ( using abstract method ) as well as code reuse through inheritance ( extending abstract class )

Comparing to concrete class they have an advantage of providing interface which a concrete class doesn't provide.

Comparing to interfaces they have an advantage of providing code reuse through inheritance which interfaces dont provide.

Sample Code for abstract class

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