Java TreeMap entrySet() Method

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Description

The Java TreeMap entrySet() method is used to return a Set view of the mappings contained in this map. The set's iterator returns the entries in ascending key order. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa.

Declaration

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

public Set<Map.Entry<K,V>> entrySet()

Parameters

NA

Return Value

The method call returns a set view of the mappings contained in this map.

Exception

NA

Getting Set of Mappings of a TreeMap of Integer,Integer Pairs Example

The following example shows the usage of Java TreeMap entrySet() method to get a set of mapping ordered in a ascending order. We've created a TreeMap object of Integer,Integer pairs. Then few entries are added to map and using entrySet() we've retrieved the set of mappings and then printed the same.

package com.tutorialspoint;

import java.util.Set;
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);

      // putting values in set
      Set mapset = treemap.entrySet();

      System.out.println("Checking value");
      System.out.println("Entry set values: "+mapset);
   }    
}

Output

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

Checking value
Entry set values: [1=1, 2=2, 3=3, 5=5, 6=6]

Getting Set of Mappings of a TreeMap of Integer,String Pairs Example

The following example shows the usage of Java TreeMap entrySet() method to get a set of mapping ordered in a ascending order. We've created a TreeMap object of Integer,String pairs. Then few entries are added to map and using entrySet() we've retrieved the set of mappings and then printed the same.

package com.tutorialspoint;

import java.util.Set;
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");

      // putting values in set
      Set mapset = treemap.entrySet();

      System.out.println("Checking value");
      System.out.println("Entry set values: "+mapset);
   }    
}

Output

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

Checking value
Entry set values: [1=one, 2=two, 3=three, 5=five, 6=six]

Getting Set of Mappings of a TreeMap of Integer,Object Pairs Example

The following example shows the usage of Java TreeMap entrySet() method to get a set of mapping ordered in a ascending order. We've created a TreeMap object of Integer,Student pairs. Then few entries are added to map and using entrySet() we've retrieved the set of mappings and then printed the same.

package com.tutorialspoint;

import java.util.Set;
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"));

      // putting values in set
      Set mapset = treemap.entrySet();

      System.out.println("Checking value");
      System.out.println("Entry set values: "+mapset);
   }    
}
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.

Checking value
Entry set values: [1=[ 1, Julie ], 2=[ 2, Robert ], 3=[ 3, Adam ], 5=[ 5, Tom ], 6=[ 6, Julia ]]