Java显式迭代器有效。 隐式的forloop产生“只能迭代java.lang.Iterable的数组或实例”

Question

I've implemented Iterable<> in my base class but the subclass will not allow an implicit forloop.

Why is the Iterator<> working correctly but the for-loop complaining of

Can only iterate over an array or an instance of java.lang.Iterable

I would have expected the Iterable<> interface to be visible in the subclass. What am I missing?

package tester;

import java.util.ArrayList;
import java.util.Iterator;

public class TestInher {

    private Concrete<Integer>   mList   = new Concrete<Integer>();

    public TestInher() {}

    public abstract class   Base<T>
        implements Iterable<T>
    {
        protected ArrayList<T>  list = new ArrayList<T>();

        @Override
        public Iterator<T> iterator() {return list.iterator();}

        public abstract void add(T item);
    }

    public abstract class   ClassAbstract<T> extends    Base<T>{}

    public class    Concrete<T>
        extends ClassAbstract<T>
    {
        @Override
        public void add(T item) {list.add(item);}
    }

    public void doIt() {
        for(int i=0; i<10; i++) {mList.add(i);}

        Iterator<Integer> i = mList.iterator(); 
        while (i.hasNext()) {
            System.out.println(i.next());
        }

        //Can only iterate over an array or an instance of java.lang.Iterable
        for(Integer i : mList.iterator()) {
        }
    }
}

Answer 1

In the enhanced for loop, you iterate over the Iterable , not over the Iterator . The Iterable gets the Iterator that is implicitly used in this loop, but an Iterable is not itself the Iterator . Try the Iterable itself.

for (Integer i : mList) {