Java Collections singletonMap() Method

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Description

The Java Collections singletonMap(K, V) method is used to get an immutable map, mapping only the specified key to the specified value.

Declaration

Following is the declaration for java.util.Collections.singletonMap() method.

public static <K,V> Map<K,V> singletonMap(K key,V value)

Parameters

• key − The sole key to be stored in the returned map.

• value − Tthe value to which the returned map maps key./p>

Return Value

The method call returns an immutable map containing only the specified key-value mapping.

Exception

NA

Getting a Singleton Map of String, Integer Example

The following example shows the usage of Java Collection singletonMap(Class,Class ) method to get a singleton map of String and Integers. We've created a Map object with a single string and integer using singletonMap(String, Integer) method and then it is printed.

package com.tutorialspoint;

import java.util.Collections;
import java.util.Map;

public class CollectionsDemo {
   public static void main(String[] a) {
      
      // create singleton map
      Map<String, Integer> map = Collections.singletonMap("A",1);

      System.out.println("Singleton map is: "+map);
   }
}

Output

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

Singleton map is: {A=1}

Getting a Singleton Map of String, Boolean Example

The following example shows the usage of Java Collection singletonMap(Class,Class ) method to get a singleton map of String and Boolean. We've created a Map object with a single string and boolean using singletonMap(String, Boolean) method and then it is printed.

package com.tutorialspoint;

import java.util.Collections;
import java.util.Map;

public class CollectionsDemo {
   public static void main(String[] a) {
      
      // create singleton map
      Map<String, Boolean> map = Collections.singletonMap("A",true);

      System.out.println("Singleton map is: "+map);
   }
}

Output

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

Singleton map is: {A=true}

Getting a Singleton Map of String, String Example

The following example shows the usage of Java Collection singletonMap(Class,Class ) method to get a singleton map of String and String. We've created a Map object with a single string and string using singletonMap(String, String) method and then it is printed.

package com.tutorialspoint;

import java.util.Collections;
import java.util.Map;

public class CollectionsDemo {
   public static void main(String[] a) {
      
      // create singleton map
      Map<String, String> map = Collections.singletonMap("A","ABC");

      System.out.println("Singleton map is: "+map);
   }
}

Output

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

Singleton map is: {A=ABC}