Java Map Interface

Java Map Interface

A map contains values based on the key i.e. key and value pair.Each pair is known as an entry.Map contains only unique elements.

Commonly used methods of Map interface:

1. public Object put(object key,Object value): is used to insert an entry in this map.
2. public void putAll(Map map):is used to insert the specified map in this map.
3. public Object remove(object key):is used to delete an entry for the specified key.
4. public Object get(Object key):is used to return the value for the specified key.
5. public boolean containsKey(Object key):is used to search the specified key from this map.
6. public boolean containsValue(Object value):is used to search the specified value from this map.
7. public Set keySet():returns the Set view containing all the keys.
8. public Set entrySet():returns the Set view containing all the keys and values.

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Entry

Entry is the subinterface of Map.So we will access it by Map.Entry name.It provides methods to get key and value.

Methods of Entry interface:

1. public Object getKey(): is used to obtain key.
2. public Object getValue():is used to obtain value.

Java HashMap class

• A HashMap contains values based on the key. It implements the Map interface and extends AbstractMap class.
• It contains only unique elements.
• It may have one null key and multiple null values.
• It maintains no order.

Hierarchy of HashMap class:

Example of HashMap class:

1.    import java.util.*;  

2.    class TestCollection13{  

3.     public static void main(String args[]){  

4.       

5.      HashMap<Integer,String> hm=new HashMap<Integer,String>();  

6.      

7.      hm.put(100,"Amit");  

8.      hm.put(101,"Vijay");  

9.      hm.put(102,"Rahul");  

10.   

11.   for(Map.Entry m:hm.entrySet()){  

12.    System.out.println(m.getKey()+" "+m.getValue());  

13.   }  

14.  }  

15. }  

Output:102 Rahul

       100 Amit

       101 Vijay

What is difference between HashSet and HashMap?

HashSet contains only values whereas HashMap contains entry(key and value).

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