Java TreeMap clear() Method

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Description

The Java TreeMap clear() method is used to remove all of the mappings from this map. The map will be empty after this call returns.

Declaration

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

public void clear()

Parameters

NA

Return Value

NA

Exception

NA

Clearing a TreeMap of Integer,Integer Pairs Example

The following example shows the usage of Java TreeMap clear() method to clear the map. We've created a TreeMap object of Integer,Integer pairs. Then few entries are added, map is printed and using clear() we're clearing the map and then again map is printed to see the effect of clear() method.

package com.tutorialspoint;

import java.util.TreeMap;

public class TreeMapDemo {
   public static void main(String[] args) {
      // creating tree map 
      TreeMap<Integer, Integer> treemap = new TreeMap<>();

      // populating tree map
      treemap.put(2, 2);
      treemap.put(1, 1);
      treemap.put(3, 3);
      treemap.put(6, 6);
      treemap.put(5, 5);

      System.out.println("Entries in the Map: "+ treemap);

      // clearing the map
      System.out.println("Clearing the Map");              
      treemap.clear();

      System.out.println("Entries in the Map: "+ treemap);
   }    
}

Output

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

Entries in the Map: {1=1, 2=2, 3=3, 5=5, 6=6}
Clearing the Map
Entries in the Map: {}

Clearing a TreeMap of Integer,String Pairs Example

The following example shows the usage of Java TreeMap clear() method to clear the map. We've created a TreeMap object of Integer,String pairs. Then few entries are added, map is printed and using clear() we're clearing the map and then again map is printed to see the effect of clear() method.

package com.tutorialspoint;

import java.util.TreeMap;

public class TreeMapDemo {
   public static void main(String[] args) {
      // creating tree map 
      TreeMap<Integer, String> treemap = new TreeMap<>();

      // populating tree map
      treemap.put(2, "two");
      treemap.put(1, "one");
      treemap.put(3, "three");
      treemap.put(6, "six");
      treemap.put(5, "five");

      System.out.println("Entries in the Map: "+ treemap);

      // clearing the map
      System.out.println("Clearing the Map");              
      treemap.clear();

      System.out.println("Entries in the Map: "+ treemap);
   }    
}

Output

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

Entries in the Map: {1=one, 2=two, 3=three, 5=five, 6=six}
Clearing the Map
Entries in the Map: {}

Clearing a TreeMap of Integer,Object Pairs Example

The following example shows the usage of Java TreeMap clear() method to clear the map. We've created a TreeMap object of Integer,Student pairs. Then few entries are added, map is printed and using clear() we're clearing the map and then again map is printed to see the effect of clear() method.

package com.tutorialspoint;

import java.util.TreeMap;

public class TreeMapDemo {
   public static void main(String[] args) {
      // creating tree map 
      TreeMap<Integer, Student> treemap = new TreeMap<>();

      // populating tree map
      treemap.put(2, new Student(2, "Robert"));
      treemap.put(1, new Student(1, "Julie"));  
      treemap.put(3, new Student(3, "Adam"));
      treemap.put(6, new Student(6, "Julia"));
      treemap.put(5, new Student(5, "Tom"));

      System.out.println("Entries in the Map: "+ treemap);

      // clearing the map
      System.out.println("Clearing the Map");              
      treemap.clear();

      System.out.println("Entries in the Map: "+ treemap);
   }    
}
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 + " ]";
   }
   @Override
   public boolean equals(Object obj) {
      if(obj == null) return false;
      Student s = (Student)obj;
      return this.rollNo == s.rollNo && this.name.equalsIgnoreCase(s.name);
   }
}

Output

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

Entries in the Map: {1=[ 1, Julie ], 2=[ 2, Robert ], 3=[ 3, Adam ], 5=[ 5, Tom ], 6=[ 5, Julia ]}
Clearing the Map
Entries in the Map: {}