javafe.filespace
Class LookAheadEnum

java.lang.Object
  javafe.filespace.LookAheadEnum

All Implemented Interfaces:

java.util.Enumeration

Direct Known Subclasses:

FilterEnum, TreeWalker, TreeWalker_ArrayEnum

abstract class LookAheadEnum

extends java.lang.Object

implements java.util.Enumeration

This layer describes how to implement an Enumeration in terms of a single function that returns the next element in a series, or null if the series is exhausted.

Using one function instead of the two used by Enumeration has the advantage of avoiding possible duplication of code to determine whether or not any elements remain in the series.

Limitation: null cannot belong to the resulting Enumerations.

Field Summary

private java.lang.Object	lookAhead
private boolean	lookAheadValid

Constructor Summary

LookAheadEnum()
Create an look-ahead enumerator that will return the non-null results of calcNextElement().

LookAheadEnum(java.lang.Object first)
Create a look-ahead enumerator that will return first followed by the non-null results of calcNextElement().

Method Summary

protected abstract java.lang.Object	calcNextElement() Compute the next element in the series, or return null if the series is exhausted.
private void	ensureLookedAhead() Ensure that lookAheadValid is set, calling calcNextElement if needed.
boolean	hasMoreElements()
java.lang.Object	nextElement()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

lookAheadValid

private boolean lookAheadValid

lookAhead

private java.lang.Object lookAhead

Constructor Detail

LookAheadEnum

public LookAheadEnum()

Create an look-ahead enumerator that will return the non-null results of calcNextElement().

LookAheadEnum

public LookAheadEnum(java.lang.Object first)

Create a look-ahead enumerator that will return first followed by the non-null results of calcNextElement().

Method Detail

ensureLookedAhead

private void ensureLookedAhead()

Ensure that lookAheadValid is set, calling calcNextElement if needed.

hasMoreElements

public final boolean hasMoreElements()

Specified by:

hasMoreElements in interface java.util.Enumeration

Returns:

true iff any more elements exist in this enumeration.

nextElement

public final java.lang.Object nextElement()

Specified by:

nextElement in interface java.util.Enumeration

calcNextElement

protected abstract java.lang.Object calcNextElement()

Compute the next element in the series, or return null if the series is exhausted. This function will never be called again once it returns null.