collections - ListIterator examples

最新推荐文章于 2024-03-13 19:26:37 发布

wangbingfeng0

最新推荐文章于 2024-03-13 19:26:37 发布

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分类专栏： Thinking in Java problems in programming

本文链接：https://blog.youkuaiyun.com/wangbingfengf98/article/details/86349582

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本文深入探讨了ListIterator在Java集合框架中的应用，对比了其与普通Iterator的区别，特别是在双向遍历和元素替换上的优势。通过具体代码示例，展示了如何创建和使用ListIterator，包括从列表特定位置开始遍历的方法。

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ListIterator is a more powerful subtype of Iterator that is produced only by List classes. While Iterator can only move forward, ListIterator is bidirectional. It can produce indices of the next and previous elements relative to where the iterator is pointing in the list, and it can replace the last element it visited using the set() method. We can produce a ListIterator that points to the beginning of the List by calling listIterator() , and we can also create a ListIterator that starts out pointing to an index n in the list by calling listIterator(n).

for easier understanding I modified the code:

// collections/ListIteration.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.

import java.util.*;
import typeinfo.pets.*;

public class ListIteration {
  public static void main(String[] args) {
    List<Pet> pets = Pets.list(8);
    ListIterator<Pet> it = pets.listIterator();
    while (it.hasNext()) {
      System.out.print(it.next() + ", " + it.nextIndex() + ", " + it.previousIndex() + "; ");
    }
    System.out.println();
    // Backwards:
    while (it.hasPrevious()) {
      System.out.print(it.previous().id() + " ");
    }
    System.out.println();
    System.out.println(pets);
    it = pets.listIterator(3);
    System.out.println("it:" + it); // private inner class ListItr does not have size() method().
    while (it.hasNext()) {
      System.out.println("it.next(): " + it.next() + "it.nextIndex(): " + it.nextIndex());
      // it.next(); // [1]
      System.out.println("Pets.get():" + Pets.get());
      it.set(Pets.get());
    }
    System.out.println(pets);
  }
}
/* My Output:
Rat, 1, 0; Manx, 2, 1; Cymric, 3, 2; Mutt, 4, 3; Pug, 5, 4; Cymric, 6, 5; Pug, 7, 6; Manx, 8, 7;
7 6 5 4 3 2 1 0
[Rat, Manx, Cymric, Mutt, Pug, Cymric, Pug, Manx]
it:java.util.ArrayList$ListItr@66d3c617
it.next(): Mutt, it.nextIndex(): 4
Pets.get():Cymric
it.next(): Pug, it.nextIndex(): 5
Pets.get():Rat
it.next(): Cymric, it.nextIndex(): 6
Pets.get():EgyptianMau
it.next(): Pug, it.nextIndex(): 7
Pets.get():Hamster
it.next(): Manx, it.nextIndex(): 8
Pets.get():EgyptianMau
[Rat, Manx, Cymric, Cymric, Rat, EgyptianMau, Hamster, EgyptianMau]
*/

[1] error is:

Rat, 1, 0; Manx, 2, 1; Cymric, 3, 2; Mutt, 4, 3; Pug, 5, 4; Cymric, 6, 5; Pug, 7, 6; Manx, 8, 7;
7 6 5 4 3 2 1 0
[Rat, Manx, Cymric, Mutt, Pug, Cymric, Pug, Manx]
it.next(): Mutt
Pets.get():Cymric
it.next(): Cymric
Pets.get():EgyptianMau
it.next(): Manx
Exception in thread "main" java.util.NoSuchElementException
        at java.util.ArrayList$Itr.next(ArrayList.java:862)
        at ListIteration.main(ListIteration.java:26)

references:

1. On Java 8 - Bruce Eckel

2. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/collections/ListIteration.java

3. http://hg.openjdk.java.net/jdk8/jdk8/jdk/file/687fd7c7986d/src/share/classes/java/util/ArrayList.java

4. https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html#next--