Java IdentityHashMap clear() Method

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Description

The clear() method is used to remove all mappings from this map.

Declaration

Following is the declaration for java.util.IdentityHashMap.clear() method.

public void clear()

Parameters

NA

Return Value

NA

Exception

NA

Clearing an IdentityHashMap of Integer, Integer Pair Example

The following example shows the usage of Java IdentityHashMap clear() method to clear a Map. We've created a Map object of Integer,Integer pairs. Then few entries are added, map is printed. Using clear() method, map is cleared and printed again.

package com.tutorialspoint;

import java.util.IdentityHashMap;

public class IdentityHashMapDemo {
   public static void main(String args[]) {
      
      // create identity hash map
      IdentityHashMap<Integer,Integer> newmap = new IdentityHashMap<>();

      // populate identity hash map
      newmap.put(1, 1);
      newmap.put(2, 2);
      newmap.put(3, 3); 

      System.out.println("Initial map elements: " + newmap);

      // clear identity hash map
      newmap.clear();

      System.out.println("Map elements after clear: " + newmap);
   }    
}

Output

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

Initial map elements: {2=2, 3=3, 1=1}
Map elements after clear: {}

Clearing an IdentityHashMap of Integer, String Pair Example

The following example shows the usage of Java IdentityHashMap clear() method to clear a Map. We've created a Map object of Integer,String pairs. Then few entries are added, map is printed. Using clear() method, map is cleared and printed again.

package com.tutorialspoint;

import java.util.IdentityHashMap;

public class IdentityHashMapDemo {
   public static void main(String args[]) {
      
      // create identity hash map
      IdentityHashMap<Integer,String> newmap = new IdentityHashMap<>();

      // populate identity hash map
      newmap.put(1, "tutorials");
      newmap.put(2, "point");
      newmap.put(3, "is best"); 

      System.out.println("Initial map elements: " + newmap);

      // clear identity hash map
      newmap.clear();

      System.out.println("Map elements after clear: " + newmap);
   }    
}

Output

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

Initial map elements: {2=point, 3=is best, 1=tutorials}
Map elements after clear: {}

Clearing an IdentityHashMap of Integer, Object Pair Example

The following example shows the usage of Java IdentityHashMap clear() method to clear a Map. We've created a Map object of Integer,Student pairs. Then few entries are added, map is printed.

package com.tutorialspoint;

import java.util.IdentityHashMap;

public class IdentityHashMapDemo {
   public static void main(String args[]) {
      
      // create identity hash map
      IdentityHashMap<Integer,Student> newmap = new IdentityHashMap<>();

      // populate identity 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("Initial map elements: " + newmap);

      // clear identity hash map
      newmap.clear();

      System.out.println("Map elements after clear: " + 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.

Initial map elements: {1=[ 1, Julie ], 3=[ 3, Adam ], 2=[ 2, Robert ]}
Map elements after clear: {}