Java HashMap put() Method

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Description

The Java HashMap put(K key, V value) method is used to associate the specified value with the specified key in this map.

Declaration

Following is the declaration for java.util.HashMap.put() method.

public V put(K key, V value)

Parameters

• key − This is the key with which the specified value is to be associated.

• value − This is the value to be associated with the specified key.

Return Value

The method call returns the previous value associated with key, or null if there was no mapping for key.

Exception

NA

Adding a key,value pair in a HashMap of Integer, Integer Pair Example

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

package com.tutorialspoint;

import java.util.HashMap;

public class HashMapDemo {
   public static void main(String args[]) {
      
      // create hash map
      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);
   }
}

Output

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

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

Adding a key,value pair in a HashMap of Integer, String Pair Example

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

package com.tutorialspoint;

import java.util.HashMap;

public class HashMapDemo {
   public static void main(String args[]) {
      
      // create hash map
      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);
   }
}

Output

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

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

Adding a key,value pair in a HashMap of Integer, Student Pair Example

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

package com.tutorialspoint;

import java.util.HashMap;

public class HashMapDemo {
   public static void main(String args[]) {
      
      // create hash map
      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);
   }
}
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: {1=[ 1, Julie ], 2=[ 2, Robert ], 3=[ 3, Adam ]}