java tutorial - Java Map Interface - java programming - learn java - java basics - java for beginners
A map contains values on the basis of key i.e. key and value pair. Each key and value pair is known as an entry. Map contains only unique keys.
- Map is useful if you have to search, update or delete elements on the basis of key.
Useful methods of Map interface
| Method | Description |
|---|---|
| Object put(Object key, Object value) | It is used to insert an entry in this map. |
| void putAll(Map map) | It is used to insert the specified map in this map. |
| Object remove(Object key) | It is used to delete an entry for the specified key. |
| Object get(Object key) | It is used to return the value for the specified key. |
| boolean containsKey(Object key) | It is used to search the specified key from this map. |
| Set keySet() | It is used to return the Set view containing all the keys. |
| Set entrySet() | It is used to return the Set view containing all the keys and values. |
Map.Entry Interface
- Entry is the sub interface of Map. So we will be accessed it by Map.Entry name. It provides methods to get key and value.
Methods of Map.Entry interface
| Method | Description |
|---|---|
| Object getKey() | It is used to obtain key. |
| Object getValue() | It is used to obtain value. |
Java Map Example: Generic (New Style)
import java.util.*;
public class MapInterfaceExample{
public static void main(String args[]){
Map<Integer,String> map=new HashMap<Integer,String>();
map.put(100,"Amit");
map.put(101,"Vijay");
map.put(102,"Rahul");
for(Map.Entry m:map.entrySet()){
System.out.println(m.getKey()+" "+m.getValue());
}
}
} click below button to copy the code. By - java tutorial - team
Output:
102 Rahul
100 Amit
101 VijayJava Map Example: Non-Generic (Old Style)
//Non-generic
import java.util.*;
public class MapExample1 {
public static void main(String[] args) {
Map map=new HashMap();
//Adding elements to map
map.put(1,"Amit");
map.put(5,"Rahul");
map.put(2,"Jai");
map.put(6,"Amit");
//Traversing Map
Set set=map.entrySet();//Converting to Set so that we can traverse
Iterator itr=set.iterator();
while(itr.hasNext()){
//Converting to Map.Entry so that we can get key and value separately
Map.Entry entry=(Map.Entry)itr.next();
System.out.println(entry.getKey()+" "+entry.getValue());
}
}
} click below button to copy the code. By - java tutorial - team
Output:
1 Amit
2 Jai
5 Rahul
6 Amit