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Java Hashtable putAll() Method

The Java Hashtable putAll(Map<? extends K,? extends V> t) method is used to copy all of the mappings from the specified Map to this Hashtable.

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

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

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

NA

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

The following example shows the usage of Java Hashtable putAll() method to put few values in a hashtable using 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 hashtable is populated using putAll() method and then printed.

package com.tutorialspoint;

import java.util.HashMap;
import java.util.Hashtable;

public class HashtableDemo {
   public static void main(String args[]) {
      
      // create hash table and map
      Hashtable<Integer,Integer> hashtable = new Hashtable<>();
	  HashMap<Integer,Integer> newmap = new HashMap<>();
 
      // populate hash map
      newmap.put(1, 1);
      newmap.put(2, 2);
      newmap.put(3, 3); 

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

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

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

The following example shows the usage of Java Hashtable putAll() method to put few values in a hashtable using 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 hashtable is populated using putAll() method and then printed.

package com.tutorialspoint;

import java.util.HashMap;
import java.util.Hashtable;

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

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

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

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

The following example shows the usage of Java Hashtable putAll() method to put few values in a hashtable using 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 hashtable is populated using putAll() method and then printed.

package com.tutorialspoint;

import java.util.HashMap;
import java.util.Hashtable;

public class HashtableDemo {
   public static void main(String args[]) {
      
      // create hash map
      Hashtable<Integer,Student> hashtable = new Hashtable<>();
      HashMap<Integer,Student> newmap = new HashMap<>();
      // 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);
      hashtable.putAll(newmap);
      System.out.println("Hashtable elements: " + hashtable);
   }    
}
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 + " ]";
   }
}

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

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

java_util_hashtable.htm

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