Collection Frame (collection traversal collection to array traversal)

Collection interface member Methods

Object[] ToArray ()
The collection can be traversed by transferring the set to the array.

Iterator Iterator ()
Iterators, private traversal of collections

 package cn.itcast_01;import java.util.arraylist;import java.util.collection;/* * Traversal of the   collection. It is actually getting each element in the collection in turn.  *  * object[] toarray (): Sets the set to the array, can implement the collection traversal  */public class  Collectiondemo3 { public static void main (String[] args)  {  //   Create Collection Object   collection c = new arraylist ();  //  add element    c.add ("Hello"); // object obj =  "Hello";  upward transformation   c.add ("World");   c.add ("Java");  //  Traversal   // object[] toarray (): Sets the set to the array, you can implement the collection of traversal   object[] objs = c.toarray ();  for  (int x = 0; x  < objs.length; x++)  {   // system.out.println (objs[x]);    //  I know that the element is a string, and I want to know the length of the element while I get the element.    // system.out.println (objs[x] +  "---" &Nbsp;+ objs[x].length ()); This code should be an error, why? Because Objs[x] is an element, and each of these elements is of type object, and the object type has no Length () method    //This paragraph why System.out.println (Objs[x] , because the ToString () method of it (Objs[x]) is called by default, and objs[x] +  "---"  + objs[x].length () needs to invoke the unique features of the string                   //  The above implementation is not possible because there is no length () method in object    //  if we want to use a string method, we must restore the element to a string    //  Down Transformation    String s =  (String)  objs[x];   system.out.println (s  +  "---"  + s.length ());   } }}

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Collection Frame (collection traversal collection to array traversal)