Implement interface Iterable & lt; T＆gt;

Java Doc

public interface Iterable
Implementing this interface allows an object to be the target of the enhanced for statement (sometimes called the “for-each loop” statement).
Since: 1.5

So what is enhanced for statement Well ？ see Java Language Specification, Do not go into , Similar to the following for sentence .

for (T t : this)
	action.accept(t);

Then we need to implement the interface , What method functions do you need to implement ？ you 're right , Namely Iterator<T> iterator() This method . This method ,Returns an iterator over elements of type T.

Realize this method , I need to return a Iterator<T> The object of ,Iterator<T> It's also an interface , We create a corresponding object , You need to implement this interface class first . The methods that this interface class needs to implement are ：

boolean hasNext();
Returns true if the iteration has more elements. (In other words, returns true if next() would return an element rather than throwing an exception.)
T next();
Returns the next element in the iteration.

According to these known , We can start to implement this interface .

Complete code

import java.util.Arrays;
import java.util.Iterator;

public class ImplementIterable implements Iterable<String> {
	private int size;
	private int current;
	private Object [] o;
	ImplementIterable() {
		size = 0;
		o = new Object [1];
	}
	public void add(String s) {
		if(size == o.length) {
			o= Arrays.copyOf(o, o.length<<1);
		}
		o[size ++] = s;
	}
	@Override
	public Iterator<String> iterator() {
		class I implements Iterator<String> {
			I() {
		        current = 0;
		    }
			@Override
			public boolean hasNext() {
				if(current < size) {
					return true;
				}
				return false;
			}
			@Override
			public String next() {
				return o[current ++].toString();
			}
		}
		return new I();
	}
	public static void main(String[] args) {
		ImplementIterable i = new ImplementIterable();
		i.add("a");
		i.add("b");
		i.add("c");
		for(String s : i) {
			System.out.println(s);
		}
	}
}