Time zone and daylight saving issue

src/main/java/org/jfree/chart/axis/DateAxis.java

@@ -873,7 +873,13 @@ else if (this.tickMarkPosition == DateTickMarkPosition.MIDDLE) {
             calendar.set(years, months, days, value, minutes, seconds);
             Date d1 = calendar.getTime();
             if (d1.getTime() >= date.getTime()) {
+                Integer previousOffset = calendar.get(Calendar.DST_OFFSET);
                 calendar.set(Calendar.HOUR_OF_DAY, value - count);
+                Integer currentOffset = calendar.get(Calendar.DST_OFFSET);
+                final boolean prevBool = previousOffset.equals(currentOffset);
+                if(!prevBool && value == 1 && currentOffset == 3_600_000){
+                    calendar.set(Calendar.DST_OFFSET, previousOffset);
+                }
                 d1 = calendar.getTime();
             }
             return d1;

src/test/java/org/jfree/chart/axis/DaylightSavingsToStandardTest.java

@@ -0,0 +1,98 @@
+package org.jfree.chart.axis;
+
+import org.jfree.data.time.Hour;
+import org.junit.jupiter.api.Test;
+import java.util.Date;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ *
+ * Issue 206 https://github.com/jfree/jfreechart/issues/206
+ * Details: Correct time is returned regardless of daylight saving time changes
+ *
+ */
+public class DaylightSavingsToStandardTest {
+
+    /**
+     * Issue 206 https://github.com/jfree/jfreechart/issues/206
+     * Details: Correct time is returned regardless of daylight saving time changes
+     *
+    * Given: Data that includes a switch from Daylight Saving time to standard
+     * Expected: Correct timezone abbreviation and hour during the change
+     * Result: Success, the expected data is returned
+     *
+     */
+    @Test
+    public void giveDaylightSavingSwitchDateAt1AM2020ExpectedCorrectTime1HourBefore() {
+        final Hour dstSwitch2020 = new Hour(1,1, 11, 2020);
+        final long timeDifference = getOneHourDifferenceInMilliseconds(dstSwitch2020);
+
+        assertEquals(3_600_000, timeDifference,"Given DST expected standard one hour before.");
+    }
+
+    /**
+     * Issue 206 https://github.com/jfree/jfreechart/issues/206
+     * Details: Correct time is returned regardless of daylight saving time changes
+     *
+    * Given: Data that includes a switch from Daylight Saving Time to standard
+     * Expected: Correct timezone abbreviation and hour during the change
+     * Result: Success, the expected data is returned
+     *
+     */
+    @Test
+    public void giveDaylightSavingSwitchDateAt1AM2021ExpectedCorrectTime1HourBefore() {
+        final Hour dstSwitch2021 = new Hour(1, 7, 11, 2021);
+        final long timeDifference = getOneHourDifferenceInMilliseconds(dstSwitch2021);
+
+        assertEquals(3_600_000, timeDifference,"Given DST expected standard one hour before.");
+    }
+
+    /**
+     * Issue 206 https://github.com/jfree/jfreechart/issues/206
+     * Details: Correct time is returned regardless of daylight saving time changes
+     *
+     * Given: Data in standard time with no time change included
+     * Expected: Correct time and abbreviation and hour during the change
+     * Result: Success, the expected data is returned
+     *
+     */
+    @Test
+    public void giveStandardDateAt1AmExpectedCorrectTime1HourBefore() {
+        final Hour standardTime = new Hour(1, 7, 12, 2018);
+        final long timeDifference = getOneHourDifferenceInMilliseconds(standardTime);
+
+        assertEquals(3_600_000, timeDifference, "Given standard expected standard one hour before.");
+    }
+
+    /**
+     * Issue 206 https://github.com/jfree/jfreechart/issues/206
+     * Details: Correct time is returned regardless of daylight saving time changes
+     *
+     * Given: Data in Daylight Saving Time with no time change included
+     * Expected: Correct time and abbreviation is returns, on hour prior
+     * Result: Success, the expected data is returned
+     *
+     */
+    @Test
+    public void giveDaylightSavingDateAt1AMExpectedCorrectTime1HourBefore() {
+        final Hour daylightDate = new Hour(1, 18, 6, 2019);
+        final long timeDifference = getOneHourDifferenceInMilliseconds(daylightDate);
+        assertEquals(3_600_000, timeDifference, "Given DST expected DST one hour before.");
+    }
+
+    /**
+    * Given: Various dates return output of previousStandardDate method
+     */
+   public long getOneHourDifferenceInMilliseconds(final Hour hour){
+        final Date testDate = new Date(hour.getFirstMillisecond());
+        final Date end = new Date(hour.getLastMillisecond());
+        final DateAxisTest.MyDateAxis axis = new DateAxisTest.MyDateAxis("Hour");
+        final DateTickUnit unit = new DateTickUnit(DateTickUnitType.HOUR, 1);
+        axis.setTickUnit(unit);
+        axis.setRange(testDate, end);
+
+       final Date previous = axis.previousStandardDate(testDate, unit);
+        return testDate.getTime() - previous.getTime();
+    }
+}