List of Java Basics

Java divides a container into storage of key-value pairs and stores ordinary objects, and map is used to store key-value pairs, and the subclasses of the collection interface are used to store ordinary objects. The set element is not repeatable, the underlying implementation is a hash table, the list of elements can be duplicated, logically, is a linear table, LinkedList is implemented with a linked list, and ArrayList is implemented with an array. The difference in function is this, then according to the specific business logic to choose it! Basic methods:Add elements: Add (Element), add (index,element) get element: Get (Index) modify element: Set (index, Element)Remove elements: Remove (Element), remove (index)Clear list: Clear ()judgment includes: Contains (Element)judgment null: IsEmpty ()List Length: size ()convert to array: ToArray ()

 　 　　　 //constructs an empty ArrayList that specifies the type of string data that is storedarraylist<string> list =NewArraylist<string>(); //A collection in Java cannot add a base data type, it must be a reference data type, or you can use a wrapper class if you want to add a base data typeList.add ("AAA"); //can increase the number of duplicate elementsList.add ("AAA"); List.add ("BBB"); //Add () is the method of inheriting collection; Add (index,element) is the List methodList.add (2, "CCC"); //Print the entire ArrayListSystem.out.println (list); //traverse individual elements and print         for(inti=0; I<list.size (); i++) {System.out.print (List.get (i)+ " "); } System.out.println ("\r\n====================================");

Output:[AAA, AAA, CCC, BBB]AAA AAA CCC BBB====================================

// Modify the element        of the position by index List.set (0, "AA");        System.out.println ("After reset, the list is:" +list);        System.out.println ("====================================");

Output

After reset, the list is: [AA, AAA, CCC, BBB]
====================================

        //from ArrayList to Array, the converted data type is Object        object[] Array = list.toarray ();          for (Object elem:array) {            + "");        }        System.out.println ("\r\nthe lenght of the array is:" + array.length);        System.out.println ("====================================");

Output

AA AAA CCC BBB
The lenght of the array is:4
====================================

    // Delete the element, you can pass in the subscript, or you can pass in the element        String  removed = list.remove (0);        System.out.println ("The removed element is:" +removed);        SYSTEM.OUT.PRINTLN (list);         boolean removed2 = List.remove ("AAA");        System.out.println (REMOVED2);        SYSTEM.OUT.PRINTLN (list);        System.out.println ("====================================");

Output:the removed element is:aa[aaa, CCC, BBB]TRUE[CCC, bbb]====================================

// Determines whether a collection contains an element        SYSTEM.OUT.PRINTLN ("list contains AAA:" +list.contains ("AAA"));         // determines whether the collection is empty        SYSTEM.OUT.PRINTLN ("List is empty?:" +List.isEmpty ());         // get the first element        System.out.println ("The fisrt element is:" + list.get (0));         System.out.println ("====================================");

Outputlist contains AAA?: Falselist is empty?: falseThe fisrt element IS:CCC====================================

// empty the entire collection         list.clear ();        System.out.println ("Afer clear, the list is:" +list);        System.out.println ("====================================");

Output:afer clear, the list is: []====================================

 //  iterate over the collection elements: Method 1  for  (int  i=0; i<list.size (); I++) {    System.out.print (List.get (i)  + "" );  //  iterate over the collection elements: Method 2  for   +" );  //  iterate over the collection elements: Method 3  iterator<    String> iterator = List.iterator ();  while   (Iterator.hasnext ()) {String El 
     = Iterator.next ();    System.out.println (EL); }

List of Java Basics