Java Map

Java Map

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Java Map

Java Map , consist of a combination of key and value . Every individual  pair of Key and Value is called Entry.

In this Article , I will step through a simple Sample program to explain what is Java Map and how to implement entry and key.

Class mapIt

  1. First i have created new class i called it “mapIt”
  2. Then i import all the library listed below
    • import java.util.HashMap;
    • import java.util.LinkedHashMap;
    • import java.util.Map;
    • import java.util.TreeMap;
  3. In this program i will create all 3 different Class ” HashMap , LinkedHashMap , TreeMap”
  4. First i create a new instance name “hash_Map” from Class HasMap
  5. And then i add the Element with key and value being assigned
  6. Finally i used the getKey() & getValue() to iterate through the “hash_Map” and print out every single element contain inside
  7. Repeat Step 3, 4,5,6 for ” LinkedHashMap , TreeMap”
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import java.util.LinkedHashMap;
import java.util.Map;
import java.util.TreeMap;
 
 
public class mapIt {
 
    public static void main(String[] args) {
         
//**********Using HashMap******************************************    
        // HashMap does not maintain the orderSequence
        // Integer is the Key
        // string is the Value
        Map<Integer,String>hash_Map = new HashMap<Integer,String>();
         
         
        // Add element with define key < integer> and Value < string > in the newly created instance Map "hash_Map"
        hash_Map.put(1, "dog");
        hash_Map.put(3, "cat");
        hash_Map.put(7, "mice");
        hash_Map.put(8, "elephant");
         
        //Iterate the Map " hash_Map"
         
        System.out.println("Iteration for hash_Map");
        for (Map.Entry<Integer, String> entry: hash_Map.entrySet()) {
            int key = entry.getKey();
            String value = entry.getValue();
            System.out.println("Key: " + key + ", value: " + value);
 
         
        }
//**********Using LinkedHashMap**************************************
         
    //*********LinkedHashMap will maintain the element Sequence*******
         
         
         
        Map<Integer, String>link_Hash_Map = new LinkedHashMap<Integer, String>();
         
    //*********Add element with key into the newly created  "link_Hash_Map"*****
         
        link_Hash_Map.put(1, "dog");
        link_Hash_Map.put(3, "cat");
        link_Hash_Map.put(7, "mice");
        link_Hash_Map.put(8, "elephant");
        //Iterate the Map " LinkedHashMap"
         
        System.out.println("Iteration for LinkedHashMap");
        for (Map.Entry<Integer, String> entry: link_Hash_Map.entrySet()) {
                    int key = entry.getKey();
                    String value = entry.getValue();
                    System.out.println("Key: " + key + ", value: " + value);
 
                 
                }
//**********Using TreeMap**************************************    
         
        //*********TreeMap will sort the element Sequence*******   
         
         
        Map <Integer ,String>tree_Map = new TreeMap<Integer, String>();
         
         
        // add new element with key into the newly
         
        tree_Map.put(1, "dog");
        tree_Map.put(3, "cat");
        tree_Map.put(7, "mice");
        tree_Map.put(8, "elephant");
        //Iterate the Map " TreeMap"
         
        System.out.println("Iteration for TreeMap");
       for (Map.Entry<Integer, String> entry: tree_Map.entrySet()) {
                            int key = entry.getKey();
                            String value = entry.getValue();
                            System.out.println("Key: " + key + ", value: " + value);
 
                         
                        }
         
         
         
 
    }
 
}

 

Useful Java Map Method

No Method Description
1 Set entrySet() Returning Set View containing all keys and value
2 Set keySet() Return Set view Value containing all keys
3 boolean containsKey(Object key)) Search the Specified Key on this map
4 Object get(Object key) Return Value of the specific key
5 Object remove(Object key) Delete the entry of the specified key.
6 void putAll(Map map) Insert the Specified Map into this map
7 Object put(Object key, Object value) Insert an entry into this map.

Check out also Set in Java here

Check Map in Java at Oracle here

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