A big wave of Java Strikes (vi) collection and iterator interfaces for the--java collection

Source: Internet
Author: User
Tags object object

This article mainly introduces the collection and iterator interfaces.

First, Collection and the Iterator Interface

Collection interface is List , Set ,, Queue the parent interface.

Collection C = new ArrayList ();

The parent class points to the child class Object! Advantages: Multi-state, dynamic link, upward transformation.

Interface-oriented programming, the caller is completely transparent to the caller, you can arbitrarily replace the subclass, shielding the subclass unique things.

Demo : Please attend: Java API documentation

Second, how to loop through the elements in the collection in turn?

Normally , when we "throw" an object into the collection, the collection forgets to change the object's data type, and the default is object. after JDK1.5, you can restrict and remember the type of the elements in the collection by using the generic type.

  1. iterator iterator OL type= "1" style= "margin-left:0.375in; direction:ltr; unicode-bidi:embed; margin-top:0in; margin-bottom:0in ">
  2. Provides a unified access interface
  3. < Span style= "Font-family:microsoft Yahei; font-size:14px "> difference: iterator for accessing objects, collecton for holding objects

public class Testiterator {public static void main (string[] args) {Collection books = new HashSet (); Books.add ("Englishbook "); Books.add (" Computerbook "); Books.add (" Musicbook "); Iterator booksiterator = Books.iterator (); while ( Booksiterator.hasnext ()) {String book = (string) booksiterator.next (); System.out.println ("book:" +book), if (Book.equals ("Computerbook")) {booksiterator.remove ();// The following code throws an exception: Concurrentmodificationexceptionbooks.remove (book);} Book= "Just a test!";} SYSTEM.OUT.PRINTLN (books);}}

Output Result:


    1. foreach , simple to use

public class Testforeach {public static void main (string[] args) {Collection books = new HashSet (); Books.add ("Englishbook" ); Books.add ("Computerbook"); Books.add ("Musicbook"); Iterator booksiterator = Books.iterator (); For (Object object: Books) {String book = (string) object; System.out.println ("book:" + book), if (Book.equals ("Computerbook")) {//books.remove (book), book = "Just a test!";}} SYSTEM.OUT.PRINTLN (books);}}
Output result :

    Three, compare two kinds of traversal mode:

    The same point: when iterating over a collection element in a loop, the system simply assigns the value of the collection element to the iteration variable. And the set itself does not change

    Difference:

    1.foreach more Concise

    2.Iterator is powerful and can operate on the elements accessed during the loop


    A big wave of Java Strikes (vi) collection and iterator interfaces for the--java collection

    Related Article

    Contact Us

    The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

    If you find any instances of plagiarism from the community, please send an email to: info-contact@alibabacloud.com and provide relevant evidence. A staff member will contact you within 5 working days.

    A Free Trial That Lets You Build Big!

    Start building with 50+ products and up to 12 months usage for Elastic Compute Service

    • Sales Support

      1 on 1 presale consultation

    • After-Sales Support

      24/7 Technical Support 6 Free Tickets per Quarter Faster Response

    • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.