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Top 10 Java Collections framework interview questions and answers

November 6, 2019November 6, 2019 sumankumar80 0 Comments java collections questions, Top 10 java collections framework interview questions

1.What are the differences between ArrayList and Vector ?

ArrayList	Vector
ArrayList is not synchronized	Vector is synchronized
ArrayList is not a legacy class	Vector is a legacy class
ArrayList increase half size of its array size when it is resized	Vector increase the double the size of its array size when it is resized
ArrayList is not thread-safe	Vector is a thread-safe

2.What is the difference between the Iterator and ListIterator ?

Iterator	ListIterator
Iterator is used to traverse the element in forward-direction only.	ListIterator is used to traverse the element in both forward and backward directions.
Iterator can use with Set,List and Queue	ListIterator can use only with List
Iterator allow only remove the element while traversing,not adding.	ListIterator allow add,remove and modify the elements while traversing the elements.

3.What is the difference between the HashMap and HashTable ?

HashMap	Hashtable
HashMap is not synchronized	Hashtable is synchronised
HashMap allow one null key and multiple null values	HashTable does not allow null key and null values.
It is very useful for the non-threaded applications	It is very useful for threaded applications.
It does not maintain insertion order that means it does not give the guarantee in which order elements are inserted ,output will be same order.	HashTable is a legacy class
HashMap inheritance AbstractMap class	HashMap inheritance Dictionary class

4.What is the comparable and comparator interface ?

Comparable interface	Comparator interface
Comparable interface provides the single way of sorting ie on the basis of only one element such as id,name or mobileNumber etc.	Comparator interface provides multiple ways of sorting ie on the basis of multiple elements such as id,name or mobileNumber etc.
We can sort the element by the CompareTo( ) method.	We can sort the element by the Compare( ) method
Comparable interface is defined in the java.lang package.	Comparator interface is defined in the java.util package
Comparable affects the original class	Comparator does not affect the original class

5.What do you mean by Collection framework in java ?

Java collections framework is the collections of classes and interfaces which is used to store and manipulate the groups of objects into a single unit.There are various classes such as ArrayList,LinkedList,Vector etc and interfaces such as Set,List and Map etc

6.What is the difference between the Set ,List and Map interface ?

Set:

It does not maintain insertion order means it depends on implementation

It does not allow duplicate element

It allows the only single null values

It does not contain legacy class

List:

It maintains the order means in which order elements are inserted,output will be in the same Order

It allows duplicate elements

It allows the many number of null values

It contains single legacy class

Map:

Map is used to store the value on the basis of key ie key-value pairs.

Map contains unique key

Map implemented class are HashMap,LinkedHashMap and TreeMap etc.

7.Write a program of storing five names using Map interface with new style.

Note:Here we will use the Map.entry( ) class which provides the two methods getKey( ) and getValue( ).

getKey( )=it is used to get key

getValue( )=It is used to get value

import java.util.*;
import java.util.List;
import java.util.ArrayList;
public class HashMapExample
{
Public static void main(String[ ] args)
{
Map<Integer,String> obj=new HashMap<Integer,String>( );
obj.put(1,”suman”);
obj.put(2,”raj”);
obj.put(3,”ajay”);
obj.put(4,”rahul”);
obj.put(5,”kumar”);

//Traversing the elements

for(Map.entry map:obj.entrySet( ))
{
System.out.println(map.getkey( )+ “ “ +map.getValue( ));
}
}
}

Output

1 suman

2 raj

3 ajay

4 rahul

5 kumar

8.How can you convert ArrayList to Array ?

We can convert ArrayList to Array using the “toArray( )” method.

import java.util.*;
import java.util.List;
import java.util.ArrayList;

Public  class ArrayListToArray
{
Public static void main(String[]  args)
{
List<integer> list=new ArrayList<Integer>( );
list.add(1);
list.add(2);
list.add(3);
list.add(4);

Integer [ ] array=new Integer[list.size];
array=list.toArray(array);

//Traversing the element
for(Integer a :array)
{
System.out.println(a+ “ “);
}
}
}

Output

9.What is the difference between the Collection and Collections ?

Collection

Collection is an interface.

Collection provides some interfaces such as List,Set and Map etc.

Collections:

Collections is a class

Collections class contains some important methods such as Collections.sort( ) and Collections.synchronizedlist( ).

10.How we cam make collection thread-safe ?

Some methods are given below makes collection thread-safe

1.Collections.synchronizedList(list)

2.Collections.synchronizedSet(set)

3.Collections.synchronizedMap(map)

Thanks and Regards

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