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

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Q1061. Explain OOPS.

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Q1062. Difference between void and return ? Can we have return statement in the void method ?

Core Java

Ans. void is a declaration that states that the method declared void is not expected to return anything.

return is a statement within the method that returns the control out of the method.

Yes, we can have return statement in the void method but without any argument.

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Q1063. In Java, if object A contains same the same data of object B, are they equal?

Core Java

Ans. it depends on the implementation of equals method of the respective class. If no definition is provided and it uses the default definition of the object class, two references are equal only if they point to the same object.

We can have such an equality defined for a particular class objects if we provide appropriate implementation of equals method comparing all those fields.

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Q1064. Is synchronized a keyword , modifier, identifier? what is it ?

Core Java

Ans. synchronized is a keyword and a modifier. The synchronized keyword is used to indicate that a method can be accessed exclusively by one thread at a time.

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Q1065. What are access and non access modifiers ?

Core Java

Ans. Access modifiers are the java reserved keywords that changes the access privileges on a class , method , element etc. For example - public , private and protected.

Non Access modifiers are the java modifiers other than access modifiers. For example - static , final, abstract, synchronized, transient, volatile etc.

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Q1066. Which of the following applies to Final ?

It is a keyword
It is a modifier
It is an access modifier

Core Java

Ans. It is a keyword and a modifier but not an access modifier.

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Q1067. Which of the following applies to "private"?

It is a keyword
It is a modifier
It is an access modifier

Core Java

Ans. Yes, all of them applies to private keyword. It is an access modifier.

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Q1068. What is a difference between Identifier and keyword ?

Core Java

Ans. Keyword is a reserved word that has a pre defined meaning for the compiler and hence cannot be used as an identifier, for example - final, private , for etc.

Identifier is the name given by the programmer to a programming construct, for example - class and method names etc.

java Keywords cannot be used as an identifier in java.

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Q1069. Can we use java keywords as identifiers ?

Core Java

Ans. No, keyword has pre defined meaning for compiler and hence cannot be used as identifiers.

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Q1070. 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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Q1071. 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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Q1072. 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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Q1073. What is the use of java.util.concurrent package in Java ?

Core Java

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Q1074. How is garbage collection in Java 8 different from Java 7 ?

Core Java

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Q1075. 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

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Q1076. 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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Q1077. 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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Q1078. Which component of MVC you like to work on ?

Java EE

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Q1079. 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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Q1080. 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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Q1081. 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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Q1082. 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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Q1083. 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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Q1084. 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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Q1085. 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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Q1086. 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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Q1087. 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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Q1088. 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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Q1089. 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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Q1090. 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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