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Java HashMap clear() Method

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

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

public void clear()

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

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("Initial map elements: " + newmap);

      // clear hash map
      newmap.clear();

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

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

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

The following example shows the usage of Java HashMap 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.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("Initial map elements: " + newmap);

      // clear hash map
      newmap.clear();

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

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

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

The following example shows the usage of Java HashMap clear() method to clear a Map. We've created a Map object of Integer,Student. Then few entries are added, 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("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 + " ]";
   }
}

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

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

java_util_hashmap.htm

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