Java Collection Class tool functions

The following code mainly calls 2 common functions of the tool class, Singletonlist and Emptylist

String[] init = {"One", "one", "three", "one", "one", "three"}; List List = new arraylist<string> (arrays.aslist (init)); SYSTEM.OUT.PRINTLN (list); List.add ("Eee"); SYSTEM.OUT.PRINTLN (list); List = Collections.singletonlist ("one"); SYSTEM.OUT.PRINTLN (list);//List.add ("eee");//System.out.println ("End"); List = Collections.emptylist (); List.add ("Eee"); SYSTEM.OUT.PRINTLN (list);

The list that they return is immutable. Singletonlist has only one element and is final.

    private static Class Singletonlist<e>extends abstractlist<e>implements randomaccess, Serializable {        Static final Long serialversionuid = 3093736618740652951L;        Private final E element;        Singletonlist (E obj)                {element = obj;}        public int size ()                   {return 1;}        Public Boolean contains (Object obj) {return eq (obj, Element);}        Public E get (int index) {            if (index! = 0)              throw new Indexoutofboundsexception ("Index:" +index+ ", size:1");            return element;        }    }

For Emptylist

  public static final List empty_list = new Emptylist ();

is to create a final empty list. As for the implementation look at the following code:

    private static Class Emptylistextends abstractlist<object>implements randomaccess, Serializable {//Use Serialversionuid from JDK 1.2.2 for interoperabilityprivate static final long Serialversionuid = 8842843931221139166l;
   public int size () {return 0;}        Public Boolean contains (Object obj) {return false;}        Public Object get (int index) {            throw new Indexoutofboundsexception ("index:" +index);        }        Preserves Singleton property        private Object readresolve () {            return empty_list;        }    }



Java Collection Class tool functions