From e79cf123db2342391b3818d685752af44f5d82d7 Mon Sep 17 00:00:00 2001
From: Moshe Rubin <moshe.rubin@gmail.com>
Date: Sun, 18 Jun 2017 05:47:04 +0300
Subject: [PATCH] Fix data selection following zooming with mouse

##The Problem##

Data selection works fine when the chart is unzoomed, with an app's ```selectionChanged()``` callback being invoked following data point selection.  When the chart is zoomed, however, the ```selectionChanged()``` callback is not invoked.

Playing with zooming shows that data selection always fails following zooming using the mouse (i.e., mouse button down + drag).  When zooming using the mouse wheel, data selection works for the first few zoom-in mouse wheel works.  Once the chart has been enlarged a few times, selection fails.

##Reproducing the Problem##

The problem can be reproduced easily  with a [minimally modified ```SelectionDemo1.java``` file](https://drive.google.com/open?id=0B09i2ZH5SsTHMmoxa3ZuMWd4WVU).

##The Technical Explanation##

Examining the FSE code shows that the reason for ```SelectionChanged()``` not being called following zooming is because the hash value of the ```DatasetSelectionExtension<XYCursor>``` object registered in function ```createDemoPanel()``` is modified because of zooming.  This causes the statement "registeredExtensions.get(dataset)" in ```DatasetExtensionManager.getExtension()``` to return null:

```java
public <T extends DatasetExtension> T getExtension(Dataset dataset,
            Class<T> interfaceClass) {
        if (interfaceClass.isAssignableFrom(dataset.getClass())) {
            //the dataset supports the interface
            return interfaceClass.cast(dataset);
        } else {
           List<DatasetExtension> extensionList
                    = registeredExtensions.get(dataset);
            if (extensionList != null) {
                for (DatasetExtension extension : extensionList) {
                    if (interfaceClass.isAssignableFrom(extension.getClass())) {
                        //the dataset does not support the extension but
                        //a matching helper object is registered for the dataset
                        return interfaceClass.cast(extension);
                    }
                }
            }
        }

        return null;
    }
```

Drilling down further shows that the ```Calendar``` member variable ```workingCalendar``` has some of its member variables changed due to zooming.

The hash returned by the ```Calendar``` class takes these into account, causing the ```HashMap get()``` to fail and return null, preventing ```selectionChanged()``` from being invoked.

For an explanation complete with screen captures, [see the following PDF file](https://drive.google.com/open?id=0B09i2ZH5SsTHZ3dpTmViWW5hRm8).

##The Proposed Fix##

I believe ```workCalendar``` is unsafe to include in the hash of a ```TimesSeriesCollection``` object and should be removed.  I would like to propose removing it from ```TimeSeriesCollection.hashCode()```.  When I made the fix locally and rebuilt FSE, data selection works perfectly on both zoomed and non-zoomed charts.
---
 src/main/java/org/jfree/data/time/TimeSeriesCollection.java | 2 --
 1 file changed, 2 deletions(-)

diff --git a/src/main/java/org/jfree/data/time/TimeSeriesCollection.java b/src/main/java/org/jfree/data/time/TimeSeriesCollection.java
index c5cc1094..9b2e1399 100644
--- a/src/main/java/org/jfree/data/time/TimeSeriesCollection.java
+++ b/src/main/java/org/jfree/data/time/TimeSeriesCollection.java
@@ -757,8 +757,6 @@ public boolean equals(Object obj) {
     public int hashCode() {
         int result;
         result = this.data.hashCode();
-        result = 29 * result + (this.workingCalendar != null
-                ? this.workingCalendar.hashCode() : 0);
         result = 29 * result + (this.xPosition != null
                 ? this.xPosition.hashCode() : 0);
         return result;