collections - Iterator design pattern examples

An Iterator (since 1.2)can remove the last element produced by next(), which means you must call next() before you call remove().

Iterator interface add new method

 default void forEachRemaining(Consumer<? super E> action)

since 1.8, Performs the given action for each remaining element until all elements have been processed or the action throws an exception. Actions are performed in the order of iteration, if that order is specified. Exceptions thrown by the action are relayed to the caller.

case 1:

Simple Iterator(design pattern) see here.

case2 : collection display:

// collections/CrossCollectionIteration.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 typeinfo.pets.*;
import java.util.*;

public class CrossCollectionIteration {
  public static void display(Iterator<Pet> it) {
    while(it.hasNext()) {
      Pet p = it.next();
      System.out.print(p.id() + ":" + p + " ");
    }
    System.out.println();
  }
  public static void main(String[] args) {
    List<Pet> pets = Pets.list(8);
    LinkedList<Pet> petsLL = new LinkedList<>(pets);
    HashSet<Pet> petsHS = new HashSet<>(pets);
    TreeSet<Pet> petsTS = new TreeSet<>(pets);
    display(pets.iterator());
    display(petsLL.iterator());
    display(petsHS.iterator());
    display(petsTS.iterator());
  }
}
/* Output:
0:Rat 1:Manx 2:Cymric 3:Mutt 4:Pug 5:Cymric 6:Pug 7:Manx
0:Rat 1:Manx 2:Cymric 3:Mutt 4:Pug 5:Cymric 6:Pug 7:Manx
0:Rat 1:Manx 2:Cymric 3:Mutt 4:Pug 5:Cymric 6:Pug 7:Manx // 4:Pug is different from 6:Pug
5:Cymric 2:Cymric 7:Manx 1:Manx 3:Mutt 6:Pug 4:Pug 0:Rat // ordered set
*/

case 3: a leaner version example:

// collections/CrossCollectionIteration2.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 typeinfo.pets.*;
import java.util.*;

public class CrossCollectionIteration2 {
  public static void display(Iterable<Pet> ip) {
    Iterator<Pet> it = ip.iterator(); // diff [1]
    while(it.hasNext()) {
      Pet p = it.next();
      System.out.print(p.id() + ":" + p + " ");
    }
    System.out.println();
  }
  public static void main(String[] args) {
    List<Pet> pets = Pets.list(8);
    LinkedList<Pet> petsLL = new LinkedList<>(pets);
    HashSet<Pet> petsHS = new HashSet<>(pets);
    TreeSet<Pet> petsTS = new TreeSet<>(pets);
    display(pets);
    display(petsLL);
    display(petsHS);
    display(petsTS);
  }
}
/* Output:
0:Rat 1:Manx 2:Cymric 3:Mutt 4:Pug 5:Cymric 6:Pug 7:Manx
0:Rat 1:Manx 2:Cymric 3:Mutt 4:Pug 5:Cymric 6:Pug 7:Manx
0:Rat 1:Manx 2:Cymric 3:Mutt 4:Pug 5:Cymric 6:Pug 7:Manx
5:Cymric 2:Cymric 7:Manx 1:Manx 3:Mutt 6:Pug 4:Pug 0:Rat
*/

[1] All of the classes are Iterable, so now the calls to display() are notably simpler.

references:

1. On Java 8 - Bruce Eckel

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

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

4. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/typeinfo/pets/Pets.java

5. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/typeinfo/pets/LiteralPetCreator.java

6. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/typeinfo/pets/PetCreator.java

7. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/collections/CrossCollectionIteration2.java

collections - Iterator design pattern examples

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