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The Open Source version of the IBM Toolbox for Java
There is a newer version: 11.1
///////////////////////////////////////////////////////////////////////////////
//
// JTOpen (IBM Toolbox for Java - OSS version)
//
// Filename:  JobEnumeration.java
//
// The source code contained herein is licensed under the IBM Public License
// Version 1.0, which has been approved by the Open Source Initiative.
// Copyright (C) 1997-2005 International Business Machines Corporation and
// others.  All rights reserved.
//
///////////////////////////////////////////////////////////////////////////////

package com.ibm.as400.access;

import java.util.Enumeration;
import java.util.NoSuchElementException;

// Helper class.  Used to wrap the Job[] with an Enumeration.
// This class is used by JobList.
class JobEnumeration implements Enumeration
{
    private Job[] jobCache_;
    private JobList list_;
    private int counter_; // number of objects returned so far by nextElement()
    private int numJobs_;
    private int listOffset_ = 0;
    private int cacheOffset_ = 0;

    private Tracker tracker_;

    JobEnumeration(JobList list, int length, Tracker tracker)
    {
        list_ = list;
        numJobs_ = length;
        tracker_ = tracker;
    }

    // Sets our tracker free if we are garbage collected, so that our parent JobList knows we are done without it having to actually maintain a hard reference to us.
    protected void finalize() throws Throwable
    {
        tracker_.set(false);
        super.finalize();
    }

    public final boolean hasMoreElements()
    {
        if (!tracker_.isSet()) return false;  // JobList invalidated us.

        if (counter_ < numJobs_)
        {
            return true;
        }
        else
        {
            tracker_.set(false);
            return false;
        }
    }

    public final Object nextElement()
    {
        if (counter_ >= numJobs_ || !tracker_.isSet())
        {
            tracker_.set(false);
            throw new NoSuchElementException();
        }

        if (jobCache_ == null || cacheOffset_ >= jobCache_.length)
        {
            try
            {
                jobCache_ = list_.getJobs(listOffset_, 1000);
                if (Trace.traceOn_) Trace.log(Trace.DIAGNOSTIC, "Loaded next block in JobEnumeration: " + jobCache_.length + " messages at list offset " + listOffset_ + " out of " + numJobs_ + " total.");
            }
            catch (Exception e)
            {
                Trace.log(Trace.ERROR, "Exception while loading nextElement() in JobEnumeration:", e);
                throw new NoSuchElementException();
            }

            // We have a freshly loaded cache, so reset to the beginning of the cache.
            cacheOffset_ = 0;

            // Set starting offset for next call to getJobs(),
            // in case another call is needed.
            listOffset_ += jobCache_.length;
        }
        ++counter_;
        return jobCache_[cacheOffset_++];
    }
}