The put(K key, V value) method of java.util.HashMap class associates the specified value with the specified key in this map. If the map previously contained a mapping for the key, the old value is replaced whereas putAll(Map<? extends K,? extends V> m) method copies all of the mappings from the specified map to this map. These mappings will replace any mappings that this map had for any of the keys currently in the specified map.
Signature
public void putAll(Map<? extends K,? extends V> m)
This method copies all of the mappings from the specified map to this map. These mappings will replace any mappings that this map had for any of the keys currently in the specified map. Throws java.lang.NullPointerException if the specified map is null
Example
The following example shows the usage of java.util.HashMap.putAll(m) method.
import java.util.HashMap; import java.util.Map; public class PutAllMethodHashMapExample { public static void main(String args[]) { // create an empty HashMap HashMap<Integer,String> hashMap1 = new HashMap<Integer,String>(); HashMap<Integer,String> hashMap2 = new HashMap<Integer,String>(); // use put() method to put elements to the HashMap1 hashMap1.put(1,"Element1"); hashMap1.put(2,"Element2"); hashMap1.put(3,"Element3"); hashMap1.put(4,"Element4"); hashMap1.put(5,"Element5"); System.out.println("**Elements of hashMap1 before putAll()**"); //Print the elements of hashMap1 for (Map.Entry<Integer,String> entry : hashMap1.entrySet()) { System.out.println("Key : "+entry.getKey()+" Value : "+entry.getValue()); } // use put() method to put elements to the HashMap2 hashMap2.put(10,"Element10"); hashMap2.put(11,"Element11"); hashMap2.put(12,"Element12"); hashMap2.put(13,"Element13"); hashMap2.put(14,"Element14"); //Put all the elements of hashMap2 to hashMap1 hashMap1.putAll(hashMap2); System.out.println("**Elements of hashMap1 after putAll()**"); //Print the elements of hashMap1 for (Map.Entry<Integer,String> entry : hashMap1.entrySet()) { System.out.println("Key : "+entry.getKey()+" Value : "+entry.getValue()); } } }
Output
**Elements of hashMap1 before putAll()** Key : 1 Value : Element1 Key : 2 Value : Element2 Key : 3 Value : Element3 Key : 4 Value : Element4 Key : 5 Value : Element5 **Elements of hashMap1 after putAll()** Key : 1 Value : Element1 Key : 2 Value : Element2 Key : 3 Value : Element3 Key : 4 Value : Element4 Key : 5 Value : Element5 Key : 10 Value : Element10 Key : 11 Value : Element11 Key : 12 Value : Element12 Key : 13 Value : Element13 Key : 14 Value : Element14
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