Fix HeatMap legend gradient asymmetry (issue #585) + cleanup

xchart-demo/src/main/java/org/knowm/xchart/standalone/issues/TestForIssue585.java

@@ -0,0 +1,121 @@
+package org.knowm.xchart.standalone.issues;
+
+import java.awt.Color;
+import java.util.ArrayList;
+import java.util.List;
+import org.knowm.xchart.HeatMapChart;
+import org.knowm.xchart.HeatMapChartBuilder;
+import org.knowm.xchart.HeatMapSeries;
+import org.knowm.xchart.SwingWrapper;
+import org.knowm.xchart.style.Styler.LegendLayout;
+import org.knowm.xchart.style.Styler.LegendPosition;
+
+/**
+ * Demonstrates issue #585 — a symmetric colormap definition produces an asymmetric legend.
+ *
+ * <p>The gradient legend bar for the Vertical layout has its LinearGradientPaint "start" point
+ * placed {@code fontSize} pixels above the actual bottom of the rectangle. This leaves a strip at
+ * the bottom that is always clamped to {@code rangeColors[0]} (the min colour), making the
+ * min-colour area visually larger than the max-colour area even when the colormap and data range
+ * are perfectly symmetric.
+ *
+ * <p>Two windows open side by side — one for each LegendPosition — so the asymmetry is visible in
+ * both orientations. The colourmap intentionally goes blue → dark → blue to make the off-centre
+ * midpoint obvious.
+ */
+public class TestForIssue585 {
+
+  public static void main(String[] args) {
+
+    new SwingWrapper<>(getChartVertical()).displayChart();
+    new SwingWrapper<>(getChartHorizontal()).displayChart();
+  }
+
+  /** Vertical legend — bug is visible here: blue band at the bottom is wider than at the top. */
+  public static HeatMapChart getChartVertical() {
+
+    HeatMapChart chart = buildChart("Issue #585 – Vertical legend (bug: asymmetric gradient)");
+    chart.getStyler().setLegendPosition(LegendPosition.OutsideE);
+    chart.getStyler().setLegendLayout(LegendLayout.Vertical);
+    chart.getStyler().setGradientColorColumnHeight(200);
+    return chart;
+  }
+
+  /** Horizontal legend — shown for comparison. */
+  public static HeatMapChart getChartHorizontal() {
+
+    HeatMapChart chart = buildChart("Issue #585 – Horizontal legend (for comparison)");
+    chart.getStyler().setLegendPosition(LegendPosition.OutsideS);
+    chart.getStyler().setLegendLayout(LegendLayout.Horizontal);
+    chart.getStyler().setGradientColorColumnHeight(200);
+    return chart;
+  }
+
+  public static HeatMapChart getChart() {
+
+    return getChartVertical();
+  }
+
+  private static HeatMapChart buildChart(String title) {
+
+    // 21-colour symmetric palette: full-blue → no-blue → full-blue
+    Color[] colors =
+        new Color[] {
+          new Color(0.0f, 0.5f, 1.0f),
+          new Color(0.0f, 0.5f, 0.9f),
+          new Color(0.0f, 0.5f, 0.8f),
+          new Color(0.0f, 0.5f, 0.7f),
+          new Color(0.0f, 0.5f, 0.6f),
+          new Color(0.0f, 0.5f, 0.5f),
+          new Color(0.0f, 0.5f, 0.4f),
+          new Color(0.0f, 0.5f, 0.3f),
+          new Color(0.0f, 0.5f, 0.2f),
+          new Color(0.0f, 0.5f, 0.1f),
+          new Color(0.0f, 0.5f, 0.0f), // middle — darkest
+          new Color(0.0f, 0.5f, 0.1f),
+          new Color(0.0f, 0.5f, 0.2f),
+          new Color(0.0f, 0.5f, 0.3f),
+          new Color(0.0f, 0.5f, 0.4f),
+          new Color(0.0f, 0.5f, 0.5f),
+          new Color(0.0f, 0.5f, 0.6f),
+          new Color(0.0f, 0.5f, 0.7f),
+          new Color(0.0f, 0.5f, 0.8f),
+          new Color(0.0f, 0.5f, 0.9f),
+          new Color(0.0f, 0.5f, 1.0f),
+        };
+
+    List<String> xData = new ArrayList<>();
+    List<String> yData = new ArrayList<>();
+    for (int i = 0; i < 5; i++) {
+      xData.add("X" + i);
+      yData.add("Y" + i);
+    }
+
+    // Data ranges symmetrically from -5 to +5
+    List<Number[]> heatData = new ArrayList<>();
+    double step = 10.0 / (xData.size() * yData.size() - 1);
+    int idx = 0;
+    for (int x = 0; x < xData.size(); x++) {
+      for (int y = 0; y < yData.size(); y++) {
+        heatData.add(new Number[] {x, y, -5.0 + step * idx});
+        idx++;
+      }
+    }
+
+    HeatMapChart chart =
+        new HeatMapChartBuilder().width(700).height(500).title(title).build();
+
+    HeatMapSeries series = chart.addSeries("heat", xData, yData, heatData);
+    series.setMin(-5.0);
+    series.setMax(5.0);
+
+    chart
+        .getStyler()
+        .setRangeColors(colors)
+        .setMin(-5.0)
+        .setMax(5.0)
+        .setLegendVisible(true);
+
+    return chart;
+  }
+}

xchart/src/main/java/org/knowm/xchart/HeatMapSeries.java

@@ -48,7 +48,7 @@ public void replaceData(List<?> xData, List<?> yData, List<Number[]> heatData) {
   protected void calculateMinMax() {
 
     min = Double.MAX_VALUE;
-    max = Double.MIN_VALUE;
+    max = -Double.MAX_VALUE;
     Number number = null;
     for (Number[] numbers : heatData) {
       if (numbers == null) {

xchart/src/main/java/org/knowm/xchart/internal/chartpart/Legend_HeatMap.java

@@ -329,7 +329,12 @@ private void paintGradient(
     Rectangle2D rect = null;
     // paint gradient color Column
     if (chart.getStyler().getLegendLayout() == Styler.LegendLayout.Vertical) {
-      start = new Point2D.Double(startx, starty + chart.getStyler().getGradientColorColumnHeight());
+      start =
+          new Point2D.Double(
+              startx,
+              starty
+                  + chart.getStyler().getLegendFont().getSize()
+                  + chart.getStyler().getGradientColorColumnHeight());
       end = new Point2D.Double(startx, starty + chart.getStyler().getLegendFont().getSize());
       rect =
           new Rectangle2D.Double(

xchart/src/main/java/org/knowm/xchart/style/BoxStyler.java

@@ -12,10 +12,7 @@ public BoxStyler() {
     super.setAllStyles();
   }
 
-  /**
-   * @deprecated Use the builder's {@code .theme(Theme)} method instead.
-   */
-  @Deprecated
+  @Override
   public void setTheme(Theme theme) {
 
     this.theme = theme;

xchart/src/main/java/org/knowm/xchart/style/BubbleStyler.java

@@ -43,13 +43,4 @@ public BubbleStyler setDefaultSeriesRenderStyle(
    *
    * @param theme
    */
-  /**
-   * @deprecated Use the builder's {@code .theme(Theme)} method instead.
-   */
-  @Deprecated
-  public void setTheme(Theme theme) {
-
-    this.theme = theme;
-    setAllStyles();
-  }
 }

xchart/src/main/java/org/knowm/xchart/style/CategoryStyler.java

@@ -259,13 +259,4 @@ public CategoryStyler setLabelsFontColorAutomaticDark(Color labelsFontColorAutom
    *
    * @param theme
    */
-  /**
-   * @deprecated Use the builder's {@code .theme(Theme)} method instead.
-   */
-  @Deprecated
-  public void setTheme(Theme theme) {
-
-    this.theme = theme;
-    setAllStyles();
-  }
 }

xchart/src/main/java/org/knowm/xchart/style/DialStyler.java

@@ -77,22 +77,6 @@ void setAllStyles() {
     labelsFont = theme.getBaseFont();
   }
 
-  /**
-   * Set the theme the styler should use
-   *
-   * @param theme
-   */
-  /**
-   * @deprecated Use the builder's {@code .theme(Theme)} method instead.
-   */
-  @Deprecated
-  public DialStyler setTheme(Theme theme) {
-
-    this.theme = theme;
-    setAllStyles();
-    return this;
-  }
-
   public boolean isCircular() {
 
     return isCircular;

xchart/src/main/java/org/knowm/xchart/style/HeatMapStyler.java

@@ -43,21 +43,6 @@ public class HeatMapStyler extends AxesChartStyler {
 
   private Function<Double, String> heatMapDecimalValueFormatter;
 
-  /**
-   * Set the theme the styler should use
-   *
-   * @param theme
-   */
-  /**
-   * @deprecated Use the builder's {@code .theme(Theme)} method instead.
-   */
-  @Deprecated
-  public void setTheme(Theme theme) {
-
-    this.theme = theme;
-    setAllStyles();
-  }
-
   @Override
   public void setAllStyles() {
 
@@ -127,8 +112,9 @@ public HeatMapStyler setRangeColors(Color[] rangeColors) {
         this.rangeColors = new Color[2];
         this.rangeColors[0] = rangeColors[0];
         this.rangeColors[1] = rangeColors[0];
+      } else {
+        this.rangeColors = rangeColors;
       }
-      this.rangeColors = rangeColors;
     } else {
       this.rangeColors = DEFAULT_RANGE_COLORS;
     }

xchart/src/main/java/org/knowm/xchart/style/HorizontalBarStyler.java

@@ -180,13 +180,4 @@ public HorizontalBarStyler setLabelsFontColorAutomaticDark(Color labelsFontColor
    *
    * @param theme
    */
-  /**
-   * @deprecated Use the builder's {@code .theme(Theme)} method instead.
-   */
-  @Deprecated
-  public void setTheme(Theme theme) {
-
-    this.theme = theme;
-    setAllStyles();
-  }
 }

xchart/src/main/java/org/knowm/xchart/style/OHLCStyler.java

@@ -43,13 +43,4 @@ public OHLCStyler setDefaultSeriesRenderStyle(OHLCSeriesRenderStyle ohlcSeriesRe
    *
    * @param theme
    */
-  /**
-   * @deprecated Use the builder's {@code .theme(Theme)} method instead.
-   */
-  @Deprecated
-  public void setTheme(Theme theme) {
-
-    this.theme = theme;
-    setAllStyles();
-  }
 }

xchart/src/main/java/org/knowm/xchart/style/PieStyler.java

@@ -346,22 +346,6 @@ public PieStyler setLabelsFontColorAutomaticDark(Color labelsFontColorAutomaticD
     return this;
   }
 
-  /**
-   * Set the theme the styler should use
-   *
-   * @param theme
-   */
-  /**
-   * @deprecated Use the builder's {@code .theme(Theme)} method instead.
-   */
-  @Deprecated
-  public PieStyler setTheme(Theme theme) {
-
-    this.theme = theme;
-    setAllStyles();
-    return this;
-  }
-
   public ClockwiseDirectionType getClockwiseDirectionType() {
     return clockwiseDirectionType;
   }

xchart/src/main/java/org/knowm/xchart/style/RadarStyler.java

@@ -84,22 +84,6 @@ public RadarStyler setStartAngleInDegrees(double startAngleInDegrees) {
     return this;
   }
 
-  /**
-   * Set the theme the styler should use
-   *
-   * @param theme
-   */
-  /**
-   * @deprecated Use the builder's {@code .theme(Theme)} method instead.
-   */
-  @Deprecated
-  public RadarStyler setTheme(Theme theme) {
-
-    this.theme = theme;
-    setAllStyles();
-    return this;
-  }
-
   public int getMarkerSize() {
 
     return markerSize;

xchart/src/main/java/org/knowm/xchart/style/Styler.java

@@ -807,7 +807,7 @@ public boolean isToolTipsAlwaysVisible() {
   /**
    * When true, all data-point labels are rendered into the chart image (visible in BitmapEncoder
    * output and Swing panels alike). This is a rendering/visual property; enable hover tooltips
-   * separately via {@link XChartPanel#setToolTipsEnabled(boolean)}.
+   * separately via {@link org.knowm.xchart.XChartPanel#setToolTipsEnabled(boolean)}.
    *
    * @param toolTipsAlwaysVisible true to render labels for every data point
    */
@@ -1029,4 +1029,16 @@ public Theme getTheme() {
 
     return theme;
   }
+
+  /**
+   * Sets the theme for this styler and re-applies all styles. Prefer constructing the chart via its
+   * builder ({@code .theme(Theme)}) over calling this method after construction.
+   *
+   * @param theme the theme to apply
+   */
+  public void setTheme(Theme theme) {
+
+    this.theme = theme;
+    setAllStyles();
+  }
 }

xchart/src/main/java/org/knowm/xchart/style/XYStyler.java

@@ -43,19 +43,6 @@ protected void setAllStyles() {
     this.cursorBackgroundColor = theme.getCursorBackgroundColor();
   }
 
-  /**
-   * Set the theme the styler should use
-   *
-   * @param theme
-   * @deprecated Use the builder's {@code .theme(Theme)} method instead.
-   */
-  @Deprecated
-  public void setTheme(Theme theme) {
-
-    this.theme = theme;
-    setAllStyles();
-  }
-
   public XYSeriesRenderStyle getDefaultSeriesRenderStyle() {
 
     return xySeriesRenderStyle;