Java WeakHashMap clear() Method

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Description

The Java WeakHashMap clear() method is used to removes all mappings from this map.

Declaration

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

public void clear()

Parameters

NA

Return Value

NA

Exception

NA

Clearing a WeakHashMap of Integer, Integer Pairs Example

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

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<>();

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

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

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

Clearing a WeakHashMap of Integer, String Pairs Example

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

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<>();

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

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

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

Clearing a WeakHashMap of Integer, Object Pairs Example

The following example shows the usage of Java WeakHashMap 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.WeakHashMap;

public class WeakHashMapDemo {
   public static void main(String args[]) {
      
      // create hash map
      WeakHashMap<Integer,Student> newmap = 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("Initial map elements: " + newmap);

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