- Java.util Package Classes
- Java.util - Home
- Java.util - ArrayDeque
- Java.util - ArrayList
- Java.util - Arrays
- Java.util - BitSet
- Java.util - Calendar
- Java.util - Collections
- Java.util - Currency
- Java.util - Date
- Java.util - Dictionary
- Java.util - EnumMap
- Java.util - EnumSet
- Java.util - Formatter
- Java.util - GregorianCalendar
- Java.util - HashMap
- Java.util - HashSet
- Java.util - Hashtable
- Java.util - IdentityHashMap
- Java.util - LinkedHashMap
- Java.util - LinkedHashSet
- Java.util - LinkedList
- Java.util - ListResourceBundle
- Java.util - Locale
- Java.util - Observable
- Java.util - PriorityQueue
- Java.util - Properties
- Java.util - PropertyPermission
- Java.util - PropertyResourceBundle
- Java.util - Random
- Java.util - ResourceBundle
- Java.util - ResourceBundle.Control
- Java.util - Scanner
- Java.util - ServiceLoader
- Java.util - SimpleTimeZone
- Java.util - Stack
- Java.util - StringTokenizer
- Java.util - Timer
- Java.util - TimerTask
- Java.util - TimeZone
- Java.util - TreeMap
- Java.util - TreeSet
- Java.util - UUID
- Java.util - Vector
- Java.util - WeakHashMap
- Java.util Package Extras
- Java.util - Interfaces
- Java.util - Exceptions
- Java.util - Enumerations
- Java.util Useful Resources
- Java.util - Useful Resources
- Java.util - Discussion
Java Collections singleton() Method
Description
The Java Collections singleton(T) method is used to return an immutable set containing only the specified object.
Declaration
Following is the declaration for java.util.Collections.singleton() method.
public static <T> Set<T> singleton(T o)
Parameters
o − This is the sole object to be stored in the returned set.
Return Value
The method call returns an immutable set containing only the specified object.
Exception
NA
Getting a Singleton Set of Integer Example
The following example shows the usage of Java Collection singleton(T) method. We've created a List object with some integers, printed the original list. Using singleton(T) method, we've removed elements of the list of given value and then printed the updated list.
package com.tutorialspoint; import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.List; public class CollectionsDemo { public static void main(String[] args) { List<Integer> list = new ArrayList<>(Arrays.asList(1,2,3,4,5)); System.out.println("Initial collection value: " + list); // remove 2 from this collection list.removeAll(Collections.singleton(2)); System.out.println("Final collection value: "+list); } }
Output
Let us compile and run the above program, this will produce the following result −
Initial collection value: [1, 2, 3, 4, 5] Final collection value: [1, 3, 4, 5]
Getting a Singleton Set of String Example
The following example shows the usage of Java Collection singleton(T) method. We've created a List object with some strings, printed the original list. Using singleton(T) method, we've removed elements of the list of given value and then printed the updated list.
package com.tutorialspoint; import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.List; public class CollectionsDemo { public static void main(String[] args) { List<String> list = new ArrayList<>(Arrays.asList("Welcome","to","Tutorialspoint")); System.out.println("Initial collection value: " + list); // remove "to" from this collection list.removeAll(Collections.singleton("to")); System.out.println("Final collection value: "+list); } }
Output
Let us compile and run the above program, this will produce the following result −
Initial collection value: [Welcome, to, Tutorialspoint] Final collection value: [Welcome, Tutorialspoint]
Getting a Singleton Set of Object Example
The following example shows the usage of Java Collection singleton(T) method. We've created a List object with some Student objects, printed the original list. Using singleton(T) method, we've removed elements of the list of given value and then printed the updated list.
package com.tutorialspoint; import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.List; public class CollectionsDemo { public static void main(String[] args) { List<Student> list = new ArrayList<>(Arrays.asList(new Student(1, "Julie"), new Student(2, "Robert"), new Student(3, "Adam"))); System.out.println("Initial collection value: " + list); // remove Robert from this collection list.removeAll(Collections.singleton(new Student(2, "Robert"))); System.out.println("Final collection value: "+list); } } 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) { 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 −
Initial collection value: [[ 1, Julie ], [ 2, Robert ], [ 3, Adam ]] Final collection value: [[ 1, Julie ], [ 3, Adam ]]
To Continue Learning Please Login
Login with Google