Java WeakHashMap putAll() Method

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Description

The Java WeakHashMap putAll(Map<? extends K,? extends V> m) method is used to copy 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.

Declaration

Following is the declaration for java.util.WeakHashMap.putAll() method.

public void putAll(Map<? extends K,? extends V> m)

Parameters

m − This is the mappings to be stored in this map.

Return Value

NA

Exception

NullPointerException − This exception is thrown if the specified map is null.

Adding multiple Key-Value Pairs to a WeakHashMap of Integer, Integer Pairs Example

The following example shows the usage of Java WeakHashMap putAll() method to put few values in a Map. We've created a Map object of Integer,Integer pairs. Then few entries are added using put() method and then map is printed. A new map is populated using putAll() method and then printed.

package com.tutorialspoint;

import java.util.WeakHashMap;

public class WeakHashMapDemo {
   public static void main(String args[]) {
      
      // create hash map
      WeakHashMap<Integer,Integer> newmap = new WeakHashMap<>();
	  WeakHashMap<Integer,Integer> newmap2 = new WeakHashMap<>();
 
      // populate hash map
      newmap.put(1, 1);
      newmap.put(2, 2);
      newmap.put(3, 3); 

      System.out.println("Map elements: " + newmap);
      newmap2.putAll(newmap);
      System.out.println("Map elements: " + newmap2); 
   }
}

Output

Let us compile and run the above program, this will produce the following result.

Map elements: {3=3, 2=2, 1=1}
Map elements: {3=3, 2=2, 1=1}

Adding multiple Key-Value Pairs to a WeakHashMap of Integer, Strings Pairs Example

The following example shows the usage of Java WeakHashMap putAll() method to put few values in a Map. We've created a Map object of Integer,String pairs. Then few entries are added using put() method and then map is printed. A new map is populated using putAll() method and then printed.

package com.tutorialspoint;

import java.util.WeakHashMap;

public class WeakHashMapDemo {
   public static void main(String args[]) {
      
      // create hash map
      WeakHashMap<Integer,String> newmap = new WeakHashMap<>();
	  WeakHashMap<Integer,String> newmap2 = new WeakHashMap<>();
      // populate hash map
      newmap.put(1, "tutorials");
      newmap.put(2, "point");
      newmap.put(3, "is best"); 

      System.out.println("Map elements: " + newmap);
      newmap2.putAll(newmap);
      System.out.println("Map elements: " + newmap2);
   }
}

Output

Let us compile and run the above program, this will produce the following result.

Map elements: {3=is best, 2=point, 1=tutorials}
Map elements: {3=is best, 2=point, 1=tutorials}

Adding multiple Key-Value Pairs to a WeakHashMap of Integer, Object Pairs Example

The following example shows the usage of Java WeakHashMap putAll() method to put few values in a Map. We've created a Map object of Integer,Student pairs. Then few entries are added using put() method and then map is printed. A new map is populated using putAll() method and then printed.

package com.tutorialspoint;

import java.util.WeakHashMap;

public class WeakHashMapDemo {
   public static void main(String args[]) {
      
      // create hash map
      WeakHashMap<Integer,Student> newmap = new WeakHashMap<>();
      WeakHashMap<Integer,Student> newmap2 = new WeakHashMap<>();
      // populate hash map
      newmap.put(1, new Student(1, "Julie"));
      newmap.put(2, new Student(2, "Robert"));
      newmap.put(3, new Student(3, "Adam"));

      System.out.println("Map elements: " + newmap);
      newmap2.putAll(newmap);
      System.out.println("Map elements: " + newmap2);
   }
}
class Student {
   int rollNo;
   String name;

   Student(int rollNo, String name){
      this.rollNo = rollNo;
      this.name = name;
   }

   @Override
   public String toString() {
      return "[ " + this.rollNo + ", " + this.name + " ]";
   }
}

Output

Let us compile and run the above program, this will produce the following result.

Map elements: {3=[ 3, Adam ], 2=[ 2, Robert ], 1=[ 1, Julie ]}
Map elements: {3=[ 3, Adam ], 2=[ 2, Robert ], 1=[ 1, Julie ]}