以前只做過LIST的迴圈列印，昨天被問到MAP迴圈怎麼弄，一下給人問蒙了，最後查API，發現Map類中有一個方法values() ，可以返回一個Collection集合容器，然後可以迴圈列印。而且發現實現了Iterable的類都可以用foreach來迴圈列印，JDK5後的新特性。
雖然說，不用實現Iterable也可以迴圈抓出容器裡的值，但是用用新特性也沒壞處。準備從Iterable開始分析。

類名：java.lang Interface Iterable<T>
方法：Iterator<T> iterator()
說明：Implementing this interface allows an object to be the target of the "foreach" statement.

[b]All Known Subinterfaces: [/b]
BeanContext, BeanContextServices, BlockingDeque<E>, BlockingQueue<E>, [b]Collection<E>, [/b]Deque<E>, DirectoryStream<T>, [b]List<E>, [/b]NavigableSet<E>, Queue<E>, [b]Set<E>, SortedSet<E>[/b]


[b]All Known Implementing Classes: [/b]
AbstractCollection, AbstractList, AbstractQueue, AbstractSequentialList, AbstractSet, ArrayBlockingQueue, ArrayDeque, [b]ArrayList[/b], AttributeList, BatchUpdateException, BeanContextServicesSupport, BeanContextSupport, ConcurrentLinkedQueue, ConcurrentSkipListSet, CopyOnWriteArrayList, CopyOnWriteArraySet, DataTruncation, DelayQueue, EnumSet, [b]HashSet[/b], JobStateReasons, LinkedBlockingDeque, LinkedBlockingQueue, [b]LinkedHashSet[/b], [b]LinkedList[/b], Path, PriorityBlockingQueue, PriorityQueue, RoleList, RoleUnresolvedList, RowSetWarning, SecureDirectoryStream, SerialException, ServiceLoader, SQLClientInfoException, SQLDataException, SQLException, SQLFeatureNotSupportedException, SQLIntegrityConstraintViolationException, SQLInvalidAuthorizationSpecException, SQLNonTransientConnectionException, SQLNonTransientException, SQLRecoverableException, SQLSyntaxErrorException, SQLTimeoutException, SQLTransactionRollbackException, SQLTransientConnectionException, SQLTransientException, SQLWarning, Stack, SyncFactoryException, SynchronousQueue, SyncProviderException, [b]TreeSet[/b], Vector


自己寫的一個類：

package test;

import java.util.Iterator;

public class IterableTest implements Iterator{

	public boolean hasNext() {
		// TODO Auto-generated method stub
		return false;
	}

	public Object next() {
		// TODO Auto-generated method stub
		return null;
	}

	public void remove() {
		// TODO Auto-generated method stub

	}

}

 

實現Iterable介面必須實現hasNext(),next(),remove三個方法。
實現的時候可以：

public class IterableTest implements Iterator<String>{
//下面的next()方法也有所改變
public String next() {
//但是不能
public class IterableTest implements Iterator<String>,Iterator<Integer>{

因為在實現方法後next方法有一個返回值，預設是Object，如果實現兩個型別不一致的介面，那麼就與“在一個類中寫兩個方法名和引數一致，而返回值不一致”的邏輯性錯誤一樣了。


待續。。。