Java EnumMap keySet() Method

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Description

The Java EnumMap keySet() method returns a Set view of the keys contained in this map.

Declaration

Following is the declaration for java.util.EnumMap.keySet() method

public Set<K> keySet()

Parameters

NA

Return Value

This method returns a set view of the keys contained in this enum map.

Exception

NA

Getting Set of Keys From an EnumMap of Enum, Integer Pairs Example

The following example shows the usage of Java EnumMap keySet() method to get a set of keys from the EnumMap instance. We've created a enum Numbers. Then EnumMap is created of enum Numbers and Integer. Few entries are added and enumMap is printed. Using keySet() method, a set of keys of enumMap is printed.

package com.tutorialspoint;

import java.util.EnumMap;

public class EnumMapDemo {
   
   // create an enum
   public enum Numbers{ONE, TWO, THREE, FOUR, FIVE}; 

   public static void main(String[] args) {
      
      EnumMap<Numbers,Integer> map = 
         new EnumMap<>(Numbers.class);

      // associate values in map
      map.put(Numbers.ONE, 1);
      map.put(Numbers.TWO, 2);
      map.put(Numbers.THREE,3);
      map.put(Numbers.FOUR, 4);

      // print the whole map
      System.out.println(map); 

      // get the key set
      System.out.println(map.keySet());
   }
}

Output

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

{ONE=1, TWO=2, THREE=3, FOUR=4}
[ONE, TWO, THREE, FOUR]

Getting Set of Keys From an EnumMap of Enum, String Pairs Example

The following example shows the usage of Java EnumMap keySet() method to get a set of keys from the EnumMap instance. We've created a enum Numbers. Then EnumMap is created of enum Numbers and Strings. Few entries are added and enumMap is printed. Using keySet() method, a set of keys of enumMap is printed.

package com.tutorialspoint;

import java.util.EnumMap;

public class EnumMapDemo {
   
   // create an enum
   public enum Numbers{ONE, TWO, THREE, FOUR, FIVE}; 

   public static void main(String[] args) {
      
      EnumMap<Numbers,String> map = 
         new EnumMap<>(Numbers.class);

      // associate values in map
      map.put(Numbers.ONE, "1");
      map.put(Numbers.TWO, "2");
      map.put(Numbers.THREE,"3");
      map.put(Numbers.FOUR, "4");

      // print the whole map
      System.out.println(map); 

      // get the key set
      System.out.println(map.keySet());
   }
}

Output

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

{ONE=1, TWO=2, THREE=3, FOUR=4}
[ONE, TWO, THREE, FOUR]

Getting Set of Keys From an EnumMap of Enum, Object Pairs Example

The following example shows the usage of Java EnumMap keySet() method to get a set of keys from the EnumMap instance. We've created a enum Numbers. Then EnumMap is created of enum Numbers and Student objects. Few entries are added and enumMap is printed. Using keySet() method, a set of keys of enumMap is printed.

package com.tutorialspoint;

import java.util.EnumMap;

public class EnumMapDemo {
   
   // create an enum
   public enum Numbers{ONE, TWO, THREE, FOUR, FIVE}; 

   public static void main(String[] args) {
      
      EnumMap<Numbers,Student> map = 
         new EnumMap<>(Numbers.class);

      // associate values in map
      map.put(Numbers.ONE, new Student(1, "Julie"));
      map.put(Numbers.TWO, new Student(2, "Robert"));
      map.put(Numbers.THREE,new Student(3, "Adam"));
      map.put(Numbers.FOUR, new Student(4, "Jene"));

      // print the whole map
      System.out.println(map); 

      // get the key set
      System.out.println(map.keySet()); 
   }
}
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 −

{ONE=[ 1, Julie ], TWO=[ 2, Robert ], THREE=[ 3, Adam ], FOUR=[ 4, Jene ]}
[ONE, TWO, THREE, FOUR]