Create singleton

static<T> Set<T> singleton(T o)
Returns an immutable set containing only the specified object.
static<T> List<T> singletonList(T o)
Returns an immutable list containing only the specified object.
static<K,V> Map<K,V>
singletonMap(K key, V value) Returns an immutable map, mapping only the specified key to the specified value.

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class MainClass {
  public static void main(String args[]) {
    String init[] = { "One", "Two", "Three", "One", "Two", "Three" };
    List list1 = new ArrayList(Arrays.asList(init));
    List list2 = new ArrayList(Arrays.asList(init));
    list1.remove("One");
    System.out.println(list1);
    list2.removeAll(Collections.singleton("One"));
    System.out.println(list2);
  }
}

The output:


[Two, Three, One, Two, Three]
[Two, Three, Two, Three]

import java.util.Collections;

public class Main {
  public static void main(String[] a){
     System.out.println(Collections.singletonList("a")); 
     System.out.println(Collections.singleton("a"));
     System.out.println(Collections.singletonMap("a","b"));
  
  }
}

The output:


[a]
[a]
{a=b}
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Collections:
  1. Collections
  2. Get empty collection from Collections
  3. Do binary search
  4. Copy value to a List
  5. Get Enumeration from collection, create list from Enumeration
  6. Fill a list
  7. Get the max and min value from a Collection
  8. Fill n Copy object to a list
  9. Replace value in a list
  10. Reverse a list
  11. Get comparator in reverse order
  12. Rotate and shuffle a list
  13. Create singleton
  14. Sort a list
  15. Swap element in a list
  16. Get a synchronized collection
  17. Return an unmodifiable view of collections