Java HashMap clear() Method

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Description

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

Declaration

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

public void clear()

Parameters

NA

Return Value

NA

Exception

NA

Clear a HashMap of Integer, Integer Pair Example

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: {}

Clear a HashMap of Integer, String Pair Example

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: {}

Clear a HashMap of Integer, Student Pair Example

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: {}