Interview questions on Collections in java for experienced

 Part 14

Interview questions on Collections in java for experienced covered in this post:

    What is the difference between HashMap and LinkedHashMap?

	HashMap	LinkedHashMap
1.	The Data Structure of HashMap is HashTable.	The Data Structure of LinkedHashMap is based on LinkedList + HashTable.
2.	HashMap doesn’t preserve the Insertion order.	LinkedHashMap preserves the insertion order.
3.	Introduced in Java 1.2	Introduced in Java1.4

 

    What is the difference between HashMap and SortedMap?

	HashMap	SortedMap
1.	HashMap is a concrete Class.	SortedMap is an interface.
2.	HashMap never preserves the insertion order.	SortedMap implementation class preserves the natural sorting order.

 

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    What is the difference between HashMap and TreeMap?

	HashMap	TreeMap
1.	The underlying data structure of HashMap is HashTable.	The underlying data structure of TreeMap is a RED-BLACK tree.
2.	HashMap allows only one null key and multiple null values.	TreeMap doesn’t allow a single null key but allows multiple null values.
3.	HashMap doesn’t maintain any order.	TreeMap maintains natural sorting order which is ascending.
4.	HashMap allows heterogeneous objects.	TreeMap allows only homogeneous objects because TreeMap inserts the elements according to some natural sorting order.
5.	Performance of HashMap is higher than TreeMap because it provides constant-time performance that is O(1) for basic operation.	The performance of TreeMap is lower than HashMap because it provides the performance of O(log(n)) for most operations.
6.	HashMap uses equals() to compare the keys.	TreeMap uses the compareTo() method to compare the keys.
7.	HashMap implements Map interface.	TreeMap implements NavigableMap interface.
8.	HashMap provides some basic methods for operation.	TreeMap provides some special methods for operation like firstKey(), lastKey(), tailMap() etc.
9.	HashMap is the best option when you don’t want the elements in some type of sorting order.	Hashtable is the best option when you want the elements in some type of sorting order.

 

    What is the difference between TreeMap and SortedMap?

	TreeMap	SortedMap
1.	TreeMap is a concrete class.	SortedMap is an interface.

 

    What is the difference between HashMap and HashTable?

	HashMap	HashTable
1.	All methods of HashMap are not synchronized.	All methods of HashTable are synchronized.
2.	HashMap is not thread-safe.	Hashtable is thread-safe.
3.	The performance of HashMap is relatively high as compared to Hashtable.	The performance of Hashtable is relatively low as compared to HashMap.
4.	Only one NULL key is allowed and multiple NULL values are allowed.	Null is not allowed either key or value otherwise it will throw NullPointerException.
5.	HashMap is not a legacy class.	Hashtable is a legacy class.
6.	HashMap introduced in Java 1.2 version.	Hashtable was introduced in Java 1.0 version.

 

• Java interview questions and answers all MNC - Click here

• Basic core java interview questions and answers for freshers - Click here

• Core java interview questions for 3 years experience - Click here

• Core java interview questions and answers for 3-5 years exp - Click here

• Core java interview questions and Answers for 5 - 7 Years exp - Click here

• Basic Java Interview Questions and Answers - Click here

• Java interview questions and answers on oops - Click here

• Java interview questions and answers on Strings - Click here

• Java interview questions on exception handling - Click here

• Interview questions on multithreading in java for experienced - Click here

• Interview questions on serialization in java for experienced - Click here

• Interview questions on inner class in java for experienced - Click here

• Interview questions on Collections in java for experienced - Click here

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