Java Tutorial/Collections/Iterable Interface

Creating Iterable Objects: using a for-each for loop on an Iterable object

   <source lang="java">

import java.util.Iterator; import java.util.NoSuchElementException; // This class supports iteration of the // characters that comprise a string. class IterableString implements Iterable<Character>, Iterator<Character> {

 private String str;
 private int count = 0;
 public IterableString(String s) {
   str = s;
 }
 // The next three methods implement Iterator.
 public boolean hasNext() {
   if (count < str.length()){
     return true;
   }  
   return false;
 }
 public Character next() {
   if (count == str.length())
     throw new NoSuchElementException();
   count++;
   return str.charAt(count - 1);
 }
 public void remove() {
   throw new UnsupportedOperationException();
 }
 // This method implements Iterable.
 public Iterator<Character> iterator() {
   return this;
 }

} public class MainClass {

 public static void main(String args[]) {
   IterableString x = new IterableString("This is a test.");
   for (char ch : x){
     System.out.println(ch);
   }
 }

}</source>

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"for" statement for Iterable object in JDK 5 has been enhanced.

It can iterate over a Collection without the need to call the iterator method. The syntax is

   <source lang="java">

for (Type identifier : expression) {

        statement (s)
    }</source>
   
  
 
  

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Iterable interface: while loop and for loop

   <source lang="java">

import java.util.Arrays; import java.util.Iterator; import java.util.List; public class MainClass {

 public static void main(String[] args) {
   List list = Arrays.asList("A", "B", "C", "D");
    Iterator iterator = list.iterator();
    while (iterator.hasNext () ) {
        String element = (String) iterator.next ();
        System.out.println(element);
    }
 }

}</source>

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Using an Iterator

The Iterator interface has the following methods:

1. hasNext.
2. next.
3. remove.

Compared to an Enumeration, hasNext() is equivalent to hasMoreElements() and next() equates to nextElement().

   <source lang="java">

import java.util.ArrayList; import java.util.Collection; import java.util.Iterator; public class MainClass {

 public static void main(String[] a) {
   Collection c = new ArrayList();
   c.add("1");
   c.add("2");
   c.add("3");
   Iterator i = c.iterator();
   while (i.hasNext()) {
     System.out.println(i.next());
   }
 }

}</source>

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