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Enable zero iterators in the chain to function 

git-svn-id: https://svn.apache.org/repos/asf/jakarta/commons/proper/collections/trunk@131480 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Stephen Colebourne 2003-12-29 16:07:53 +00:00
parent e6d11cfee8
commit 5215e27ed6
2 changed files with 86 additions and 88 deletions
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155
src/java/org/apache/commons/collections/iterators/IteratorChain.java
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@ -1,5 +1,5 @@
/*
* $Header: /home/jerenkrantz/tmp/commons/commons-convert/cvs/home/cvs/jakarta-commons//collections/src/java/org/apache/commons/collections/iterators/IteratorChain.java,v 1.7 2003/12/03 11:37:44 scolebourne Exp $
* $Header: /home/jerenkrantz/tmp/commons/commons-convert/cvs/home/cvs/jakarta-commons//collections/src/java/org/apache/commons/collections/iterators/IteratorChain.java,v 1.8 2003/12/29 16:07:53 scolebourne Exp $
* ====================================================================
*
* The Apache Software License, Version 1.1
@ -61,57 +61,61 @@ import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import org.apache.commons.collections.IteratorUtils;
import org.apache.commons.collections.list.UnmodifiableList;
/**
* <p>An IteratorChain is an Iterator that wraps one or
* more Iterators. When any method from the
* Iterator interface is called, the IteratorChain will
* proxy to a single underlying Iterator. The
* IteratorChain will invoke the Iterators in sequence until
* all Iterators are exhausted completely.</p>
*
* <p>Under many circumstances, linking Iterators together
* in this manner is more efficient (and convenient)
* than reading out the contents of each Iterator into a
* List and creating a new Iterator.</p>
*
* <p>Calling a method that adds new Iterator<i>after
* a method in the Iterator interface
* has been called</i> will result in an
* UnsupportedOperationException. Subclasses should <i>take care</i>
* to not alter the underlying List of Iterators.</p>
* An IteratorChain is an Iterator that wraps a number of Iterators.
* <p>
* This class makes mutiple iterators look like one to the caller
* When any method from the Iterator interface is called, the IteratorChain
* will delegate to a single underlying Iterator. The IteratorChain will
* invoke the Iterators in sequence until all Iterators are exhausted.
* <p>
* Under many circumstances, linking Iterators together in this manner is
* more efficient (and convenient) than reading out the contents of each
* Iterator into a List and creating a new Iterator.
* <p>
* Calling a method that adds new Iterator<i>after a method in the Iterator
* interface has been called</i> will result in an UnsupportedOperationException.
* Subclasses should <i>take care</i> to not alter the underlying List of Iterators.
* <p>
* NOTE: As from version 3.0, the IteratorChain may contain no
* iterators. In this case the class will function as an empty iterator.
*
* @since Commons Collections 2.1
* @version $Revision: 1.7 $ $Date: 2003/12/03 11:37:44 $
* @version $Revision: 1.8 $ $Date: 2003/12/29 16:07:53 $
*
* @author Morgan Delagrange
* @author Stephen Colebourne
*/
public class IteratorChain implements Iterator {
/** The chain of iterators */
protected final List iteratorChain = new ArrayList();
/** The index of the current iterator */
protected int currentIteratorIndex = 0;
/** The current iterator */
protected Iterator currentIterator = null;
// the "last used" Iterator is the Iterator upon which
// next() or hasNext() was most recently called
// used for the remove() operation only
/**
* The "last used" Iterator is the Iterator upon which
* next() or hasNext() was most recently called
* used for the remove() operation only
*/
protected Iterator lastUsedIterator = null;
// ComparatorChain is "locked" after the first time
// compare(Object,Object) is called
/**
* ComparatorChain is "locked" after the first time
* compare(Object,Object) is called
*/
protected boolean isLocked = false;
// Constructors
// -------------------------------------------------------------------
//-----------------------------------------------------------------------
/**
* Construct an IteratorChain with no Iterators.
* You must add at least Iterator before calling
* any method from the Iterator interface, or an
* UnsupportedOperationException is thrown
* <p>
* You will normally use {@link #addIterator(Iterator)} to add
* some iterators after using this constructor.
*/
public IteratorChain() {
super();
@ -172,9 +176,7 @@ public class IteratorChain implements Iterator {
}
}
// Public Methods
// -------------------------------------------------------------------
//-----------------------------------------------------------------------
/**
* Add an Iterator to the end of the chain
*
@ -226,74 +228,64 @@ public class IteratorChain implements Iterator {
}
/**
* Determine if modifications can still be made to the
* IteratorChain. IteratorChains cannot be modified
* once they have executed a method from the Iterator
* interface.
* Determine if modifications can still be made to the IteratorChain.
* IteratorChains cannot be modified once they have executed a method
* from the Iterator interface.
*
* @return true = IteratorChain cannot be modified; false =
* IteratorChain can still be modified.
* @return true if IteratorChain cannot be modified, false if it can
*/
public boolean isLocked() {
return isLocked;
}
// throw an exception if the IteratorChain is locked
/**
* Checks whether the iterator chain is now locked and in use.
*/
private void checkLocked() {
if (isLocked == true) {
throw new UnsupportedOperationException("IteratorChain cannot be changed after the first use of a method from the Iterator interface");
}
}
private void checkChainIntegrity() {
if (iteratorChain.size() == 0) {
throw new UnsupportedOperationException("IteratorChains must contain at least one Iterator");
}
}
// you MUST call this method whenever you call a method in the Iterator interface, because
// this method also assigns the initial value of the currentIterator variable
/**
* Lock the chain so no more iterators can be added.
* This must be called from all Iterator interface methods.
*/
private void lockChain() {
if (isLocked == false) {
checkChainIntegrity();
isLocked = true;
}
}
// call this before any Iterator method to make sure that the current Iterator
// is not exhausted
/**
* Updates the current iterator field to ensure that the current Iterator
* is not exhausted
*/
protected void updateCurrentIterator() {
if (currentIterator == null) {
currentIterator = (Iterator) iteratorChain.get(0);
if (iteratorChain.isEmpty()) {
currentIterator = IteratorUtils.EMPTY_ITERATOR;
} else {
currentIterator = (Iterator) iteratorChain.get(0);
}
// set last used iterator here, in case the user calls remove
// before calling hasNext() or next() (although they shouldn't)
lastUsedIterator = currentIterator;
}
if (currentIteratorIndex == (iteratorChain.size() - 1)) {
return;
}
while (currentIterator.hasNext() == false) {
++currentIteratorIndex;
while (currentIterator.hasNext() == false && currentIteratorIndex < iteratorChain.size() - 1) {
currentIteratorIndex++;
currentIterator = (Iterator) iteratorChain.get(currentIteratorIndex);
if (currentIteratorIndex == (iteratorChain.size() - 1)) {
return;
}
}
}
//-----------------------------------------------------------------------
/**
* Return true if any Iterator in the IteratorChain has a remaining
* element.
* Return true if any Iterator in the IteratorChain has a remaining element.
*
* @return true if elements remain
* @exception UnsupportedOperationException
* if the IteratorChain does not contain at least one
* Iterator
*/
public boolean hasNext() throws UnsupportedOperationException {
public boolean hasNext() {
lockChain();
updateCurrentIterator();
lastUsedIterator = currentIterator;
@ -305,13 +297,9 @@ public class IteratorChain implements Iterator {
* Returns the next Object of the current Iterator
*
* @return Object from the current Iterator
* @exception NoSuchElementException
* if all the Iterators are exhausted
* @exception UnsupportedOperationException
* if the IteratorChain does not contain at least one
* Iterator
* @throws NoSuchElementException if all the Iterators are exhausted
*/
public Object next() throws NoSuchElementException, UnsupportedOperationException {
public Object next() {
lockChain();
updateCurrentIterator();
lastUsedIterator = currentIterator;
@ -327,20 +315,17 @@ public class IteratorChain implements Iterator {
* UnsupportedOperationException if the underlying
* Iterator does not support this method.
*
* @exception UnsupportedOperationException
* if the remove operator is not supported by the underlying
* Iterator or if there are no Iterators in the IteratorChain
* @exception IllegalStateException
* if the next method has not yet been called, or the
* remove method has already been called after the last
* call to the next method.
* @throws UnsupportedOperationException
* if the remove operator is not supported by the underlying Iterator
* @throws IllegalStateException
* if the next method has not yet been called, or the remove method has
* already been called after the last call to the next method.
*/
public void remove() throws UnsupportedOperationException, IllegalStateException {
public void remove() {
lockChain();
updateCurrentIterator();
lastUsedIterator.remove();
}
}

19
src/test/org/apache/commons/collections/iterators/TestIteratorChain.java
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@ -1,5 +1,5 @@
/*
* $Header: /home/jerenkrantz/tmp/commons/commons-convert/cvs/home/cvs/jakarta-commons//collections/src/test/org/apache/commons/collections/iterators/TestIteratorChain.java,v 1.6 2003/10/01 21:54:55 scolebourne Exp $
* $Header: /home/jerenkrantz/tmp/commons/commons-convert/cvs/home/cvs/jakarta-commons//collections/src/test/org/apache/commons/collections/iterators/TestIteratorChain.java,v 1.7 2003/12/29 16:07:53 scolebourne Exp $
* ====================================================================
*
* The Apache Software License, Version 1.1
@ -68,7 +68,7 @@ import junit.framework.TestSuite;
/**
* Tests the IteratorChain class.
*
* @version $Revision: 1.6 $ $Date: 2003/10/01 21:54:55 $
* @version $Revision: 1.7 $ $Date: 2003/12/29 16:07:53 $
*
* @author James Strachan
* @author Mauricio S. Moura
@ -180,5 +180,18 @@ public class TestIteratorChain extends AbstractTestIterator {
assertEquals("C",chain.next());
assertTrue("should not have next",!chain.hasNext());
}
public void testEmptyChain() {
IteratorChain chain = new IteratorChain();
assertEquals(false, chain.hasNext());
try {
chain.next();
fail();
} catch (NoSuchElementException ex) {}
try {
chain.remove();
fail();
} catch (IllegalStateException ex) {}
}
}