com.tangosol.util.SimpleEnumerator Maven / Gradle / Ivy
/*
* Copyright (c) 2000, 2020, Oracle and/or its affiliates.
*
* Licensed under the Universal Permissive License v 1.0 as shown at
* http://oss.oracle.com/licenses/upl.
*/
package com.tangosol.util;
import java.lang.reflect.Array;
import java.util.Collection;
import java.util.Iterator;
import java.util.Enumeration;
import java.util.NoSuchElementException;
import java.util.ArrayList;
/**
* Provide a generic implementation of an array enumerator.
*
* @author Cameron Purdy
* @version 0.50, 09/05/97
* @version 1.00, 08/07/98
*/
@SuppressWarnings("unchecked")
public class SimpleEnumerator
extends Base
implements Enumeration, Iterator
{
// ----- constructors ---------------------------------------------------
/**
* Construct the simple enumerator based on an array of objects.
*
* @param aoItem array of objects to enumerate
*/
public SimpleEnumerator(E[] aoItem)
{
// iterate forwards, don't copy the array
this(aoItem, 0, aoItem.length, true, false);
}
/**
* Construct the simple enumerator based on an array of objects.
*
* @param aoItem array of objects to enumerate
* @param ofStart the first object position
* @param cItems the number of objects to enumerate
*/
public SimpleEnumerator(E[] aoItem, int ofStart, int cItems)
{
// iterate forwards, don't copy the array
this(aoItem, ofStart, cItems, true, false);
}
/**
* Construct the simple enumerator based on an array of objects, making
* a copy of the array if specified.
*
* @param aoItem array of objects to enumerate
* @param ofStart the first object position
* @param cItems the number of objects to enumerate
* @param fForward true to iterate forwards, false to iterate from the
* end backwards to the beginning
* @param fCopy pass true to make a copy of the array or false if the
* array's contents will not change
*/
public SimpleEnumerator(E[] aoItem, int ofStart, int cItems,
boolean fForward, boolean fCopy)
{
if (cItems < 0)
{
throw new IllegalArgumentException("Negative count");
}
if (fForward
? ofStart < 0 || ofStart + cItems > aoItem.length
: ofStart >= aoItem.length || ofStart - cItems < 0)
{
throw new IllegalArgumentException("Off limits");
}
// only copy if there are at least two items in the iterator
if (fCopy && cItems > 1)
{
aoItem = aoItem.clone();
}
m_aoItem = aoItem;
m_fForward = fForward;
m_iItem = ofStart;
m_ofLimit = fForward ? ofStart + cItems : ofStart - cItems;
}
/**
* Construct a simple enumerator based on another Enumeration. This forces
* an initial pass through the elements of the passed enumerator, making
* a copy of that data, thus capturing a "point in time" view of an
* Enumeration which may be backed by mutable data. In other words, this
* constructs a "safe enumerator" based on a "not-safe enumerator".
*
* @param enmr the java.util.Enumeration to enumerate
*/
public SimpleEnumerator(Enumeration enmr)
{
this(toArray(enmr));
}
/**
* Construct a simple enumerator based on another Iterator. This forces
* an initial pass through the elements of the passed enumerator, making
* a copy of that data, thus capturing a "point in time" view of an
* Iterator which may be backed by mutable data. In other words, this
* constructs a "safe enumerator" based on a "not-safe enumerator".
*
* @param iter the java.util.Iterator to enumerate
*/
public SimpleEnumerator(Iterator iter)
{
this(toArray(iter));
}
/**
* Construct a simple enumerator based on a collection.
*
* @param col the java.util.Collection to enumerate
*/
public SimpleEnumerator(Collection col)
{
this((E[]) col.toArray());
}
// ----- Enumeration interface ------------------------------------------
/**
* Tests if this enumeration contains more elements.
*
* @return true if the enumeration contains more elements, false otherwise
*/
public boolean hasMoreElements()
{
return hasNext();
}
/**
* Returns the next element of this enumeration.
*
* @return the next element in the enumeration
*/
public E nextElement()
{
return next();
}
// ----- Iterator interface ---------------------------------------------
/**
* Tests if this Iterator contains more elements.
*
* @return true if the Iterator contains more elements, false otherwise
*/
public boolean hasNext()
{
return m_fForward ? m_iItem < m_ofLimit : m_iItem > m_ofLimit;
}
/**
* Returns the next element of this Iterator.
*
* @return the next element in the Iterator
*/
public E next()
{
if (!hasNext())
{
throw new NoSuchElementException();
}
try
{
E o = m_aoItem[m_iItem];
if (m_fForward)
{
m_iItem++;
}
else
{
m_iItem--;
}
return o;
}
catch (ArrayIndexOutOfBoundsException e)
{
throw new NoSuchElementException();
}
}
/**
* Remove the last-returned element that was returned by the Iterator.
* This method always throws UnsupportedOperationException because the
* Iterator is immutable.
*/
public void remove()
{
throw new UnsupportedOperationException("iterator is immutable");
}
// ----- Enumeration helpers --------------------------------------------
/**
* Turns an enumeration into an array.
*
* @param enmr the enumerator
*
* @return an array of the objects from the enumerator
*/
public static T[] toArray(Enumeration enmr)
{
if (!enmr.hasMoreElements())
{
return (T[]) NO_OBJECTS;
}
if (enmr instanceof SimpleEnumerator)
{
return (T[]) ((SimpleEnumerator) enmr).toArray();
}
ArrayList list = new ArrayList<>();
do
{
list.add(enmr.nextElement());
}
while (enmr.hasMoreElements());
return (T[]) list.toArray();
}
/**
* Turns an enumeration into an array. The behavior of this method differs
* from the simple {@link #toArray(Enumeration)} method in the same way
* that the {@link Collection#toArray(Object[])} method differs from the
* {@link Collection#toArray()} method.
*
* @param enmr the enumerator
* @param ao the array into which the elements of the Enumeration are
* to be stored, if it is big enough; otherwise, a new array
* of the same runtime type is allocated for this purpose
*
* @return an array of the objects from the enumerator
*/
public static T[] toArray(Enumeration enmr, T[] ao)
{
if (!enmr.hasMoreElements())
{
if (ao.length > 0)
{
ao[0] = null;
}
return ao;
}
if (enmr instanceof SimpleEnumerator)
{
return (T[]) ((SimpleEnumerator) enmr).toArray(ao);
}
ArrayList list = new ArrayList<>();
do
{
list.add(enmr.nextElement());
}
while (enmr.hasMoreElements());
return ao == null ? (T[]) list.toArray() : list.toArray(ao);
}
/**
* Turns an Iterator into an array.
*
* @param iter the Iterator
*
* @return an array of the objects
*/
public static T[] toArray(Iterator iter)
{
if (!iter.hasNext())
{
return (T[]) NO_OBJECTS;
}
if (iter instanceof SimpleEnumerator)
{
return (T[]) ((SimpleEnumerator) iter).toArray();
}
ArrayList list = new ArrayList();
do
{
list.add(iter.next());
}
while (iter.hasNext());
return (T[]) list.toArray();
}
/**
* Turns an Iterator into an array. The behavior of this method differs
* from the simple {@link #toArray(Iterator)} method in the same way that
* the {@link Collection#toArray(Object[])} method differs from the
* {@link Collection#toArray()} method.
*
* @param iter the Iterator
* @param ao the array into which the elements of the Iterator are
* to be stored, if it is big enough; otherwise, a new array
* of the same runtime type is allocated for this purpose
*
* @return an array of the objects from the Iterator
*/
public static T[] toArray(Iterator iter, T[] ao)
{
if (!iter.hasNext())
{
if (ao == null)
{
ao = (T[]) NO_OBJECTS;
}
else if (ao.length > 0)
{
ao[0] = null;
}
return ao;
}
if (iter instanceof SimpleEnumerator)
{
return (T[]) ((SimpleEnumerator) iter).toArray(ao);
}
ArrayList list = new ArrayList<>();
do
{
list.add(iter.next());
}
while (iter.hasNext());
return ao == null ? (T[]) list.toArray() : list.toArray(ao);
}
// ----- Collection-like helpers ----------------------------------------
/**
* Return the remaining contents of this SimpleEnumerator as an array.
*
* @return an array containing all of the elements in this enumerator
*/
public Object[] toArray()
{
return toArray((Object[]) null);
}
/**
* Return the remaining contents of this SimpleEnumerator as an array of
* the type specified by the passed array, and use that passed array to
* store the values if it is big enough, putting a null in the first
* unused element if the size of the passed array is bigger than the
* number of remaining elements in this enumerator, as per the contract
* of the {@link Collection#toArray(Object[])} method.
*
* @param ao the array into which the elements of the Enumeration are
* to be stored, if it is big enough; otherwise, a new array
* of the same runtime type is allocated for this purpose
*
* @return an array containing the elements of the collection
*
* @throws ArrayStoreException if the runtime type of the specified array
* is not a supertype of the runtime type of every element in this
* collection
*/
public T[] toArray(T[] ao)
{
E[] aoItem = m_aoItem;
int iNext = m_iItem;
int iLast = m_ofLimit;
boolean fForward = m_fForward;
// create the array to store the map contents
int co = fForward ? iLast - iNext : iNext - iLast;
if (ao == null)
{
// implied Object[] type, see toArray()
ao = (T[]) new Object[co];
}
else if (ao.length < co)
{
// if it is not big enough, a new array of the same runtime
// type is allocated
ao = (T[]) Array.newInstance(ao.getClass().getComponentType(), co);
}
else if (ao.length > co)
{
// if the collection fits in the specified array with room to
// spare, the element in the array immediately following the
// end of the collection is set to null
ao[co] = null;
}
if (fForward)
{
System.arraycopy(aoItem, iNext, ao, 0, co);
}
else
{
int i = 0;
while (iNext > iLast)
{
ao[i++] = (T) aoItem[iNext--];
}
}
// set the enumerator to "finished"
m_iItem = iLast;
return ao;
}
// ----- constants ------------------------------------------------------
/**
* An array of no items.
*/
private static final Object[] NO_OBJECTS = new Object[0];
// ----- data members ---------------------------------------------------
/**
* Array of items to enumerate.
*/
protected E[] m_aoItem;
/**
* Iterator position: next item to return.
*/
protected int m_iItem;
/**
* Iterator end position (beyond last).
*/
protected int m_ofLimit;
/**
* Iterator direction.
*/
protected boolean m_fForward;
}
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