Core Java - Interview Questions and Answers for 'Basic' | Search Interview Question

Interview Questions and Answers - Order By Newest

Usually asked to entry level software developers.

Q61. Write a program to swap two variables without using third

Core Java

Ans. public static void main(String[] args) {
   int num1 = 1;
   int num2 = 2;
   num1 = num1^num2;
   num2 = num1^num2;
   num1 = num1^num2;
   System.out.print("num1 = " + num1 +", num2 = "+num2);
}

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Q62. 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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Q63. What is JSON ?

Json

Ans. JSON is "JavaScript Object Notation", primarily used for client-server or server-server communication. Its a much lighter and readable alternative to XML. JSON is language independent and is easily parse-able in all programming languages.

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Q64. What is an API ( Application Programming Interface ) ?

Ans. An API is a kind of technical contract which defines functionality that two parties must provide: a service provider (often called an implementation) and an application. an API simply defines services that a service provider (i.e., the implementation) makes available to applications.

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Q65. What is URL?

Java EE

Ans. URL is Uniform Resource Locator which is representation of HTTP address.

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Q66. What is HTTP ?

Java EE

Ans. HTTP or Hypertext Transfer Protocol is internet protocol for tranmission of hypertext ( text with meta data ) over internet.

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Q67. Which access specifier can be used with Class ?

Core Java

Ans. For top level class we can only use "public" and "default". We can use private with inner class.

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Q68. Different ways of implementing Threads in Java ?

Core Java

Ans. Threads in Java can be implement either by Extending Thread class or implementing runnable interface.

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Q69. What is a Final Method ?

Core Java

Ans. A Method that cannot be overriden in the sub class.

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Very Frequently asked.Favorite question in Walk in drive for many Indian service companies.

Q70. What is a Final Class ?

Ans. A Class that cannot be sub classed.

Sample Code for final class

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Very frequently asked. Usually asked with questions related to String. Frequently asked at CTS / Cognizant

Q71. What is an Immutable Object ?

Core Java

Ans. Object that can't be changed after instantiation.

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Q72. Name few Java Exceptions ?

Core Java

Ans. IndexOutofBoundException ,
NoClassDefFoundException ,
OutOfMemoryException ,
IllegalArgumentException,
NullPointerException,
IllegalStateException

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Q73. How can we make sure that a code segment gets executed even in case of uncatched exceptions ?

Ans. By putting it within finally.

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Q74. What is "super" used for ?

Ans. Used to access members of the base class.

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Q75. What is "this" keyword used for ?

Ans. Used to represent an instance of the class in which it appears.

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Q76. Difference between boolean and Boolean ?

Core Java

Ans. boolean is a primitive type whereas Boolean is a class.

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Q77. Difference between Serialization and Deserialization ?

Core Java

Ans. Serialization is the process of writing the state of an object to a byte stream. Deserialization is the process of restoring these objects.

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Q78. What is an Enum type ?

Core Java

Ans. An enum type is a special data type that enables for a variable to be a set of predefined constants

Sample Code for enum

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Q79. What is a Static import ?

Core Java

Ans. By static import , we can access the static members of a class directly without prefixing it with the class name.

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Q80. Difference between Map and HashMap ?

Core Java

Ans. Map is an interface where HashMap is the concrete class.

Sample Code for map

Sample Code for hashmap

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Frequently asked to fresh graduates.

Q81. Is JVM, a compiler or interpretor ?

Ans. Its an interpretor.

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Q82. Is it necessary that each try block to be followed by catch block ?

Core Java

Ans. It should be followed by either catch or finally block.

Sample Code for Retry in case of exception

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Q83. Difference between nested and inner classes ?

Ans. Inner class is a type of nested class.

Inner classes are non static nested classes i.e the one that are associated with the instance of outer class.

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Q84. what is the difference between collections class vs collections interface ?

Core Java

Ans. Collections class is a utility class having static methods for doing operations on objects of classes which implement the Collection interface. For example, Collections has methods for finding the max element in a Collection.

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Q85. What is XML ?

Xml

Ans. XML or eXtensible Markup Language is a markup languages for describing data and its metadata.

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Frequently asked in CTS ( Based on 2 feedback )

Q86. What is the difference between comparable and comparator in java.util pkg?

Core Java

Ans. Comparable interface is used for single sequence sorting i.e.sorting the objects based on single data member where as comparator interface is used to sort the object based on multiple data members.

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Q87. Advantage of Collection classes over Arrays ?

Core Java

Ans. Collections are re-sizable in nature. We can increase or decrease the size as per recruitment.
Collections can hold both homogeneous and heterogeneous data's.
Every collection follows some standard data structures.
Collection provides many useful built in methods for traversing,sorting and search.

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Q88. What is the difference between float and double?

Ans. Float can represent up to 7 digits accurately after decimal point, where as double can represent up to 15 digits accurately after decimal point.

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Q89. What are the features of encapsulation ?

Core Java

Ans. Combine the data of our application and its manipulation at one place.

Encapsulation Allow the state of an object to be accessed and modified through behaviors.

Reduce the coupling of modules and increase the cohesion inside them.

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Q90. Write a method to check if input String is Palindrome?

Core Java

Ans. private static boolean isPalindrome(String str) {

if (str == null)
return false;

StringBuilder strBuilder = new StringBuilder(str);

strBuilder.reverse();

return strBuilder.toString().equals(str);

}

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