BE THE CODER > Java > Collections > Singleton Collection

The following example shows how to create singleton collection. The Collections class provides several type safe methods which returns an immutable collection containing only the specified object. The returned collection is serializable.

File Name :	com/bethecoder/tutorials/utils/collections/SingletonCollection.java
Author :	Sudhakar KV
Email :	[email protected]


package com.bethecoder.tutorials.utils.collections;



import java.util.Collection;

import java.util.Collections;

import java.util.List;

import java.util.Map;

import java.util.Set;



public class SingletonCollection {



  /**

   * @param args

   */

  public static void main(String[] args) {



    //singleton list of Strings

    List<String> strList = Collections.<String>singletonList("Hello World");

    print(strList);

    

    //singleton list of Booleans

    List<Boolean> boolList = Collections.<Boolean>singletonList(true);

    print(boolList);

    

    //singleton list of Employees

    List<Person> empList = Collections.<Person>singletonList(new Person("One"));

    print(empList);

    

    //singleton Set of Employees

    Set<Person> empSet = Collections.<Person>singleton(new Person("Two"));

    print(empSet);

    

    //singleton Map of Employees

    Map<String, Person> empMap = Collections.<String, Person>singletonMap("3", new Person("Three"));

    System.out.println(empMap + " size : " + empMap.size());

  }



  public static void print(Collection<?> collection) {

    System.out.println(collection + " size : " + collection.size());

  }

}



class Person {

  private String name;



  public Person(String name) {

    super();

    this.name = name;

  }

  

  public String getName() {

    return name;

  }



  public void setName(String name) {

    this.name = name;

  }

  

  public String toString() {

    return "[Person : " + name + "]";

  }

}