Add setRandom(Random) to RandomPointsBuilder

modules/core/src/main/java/org/locationtech/jts/shape/random/RandomPointsBuilder.java

@@ -12,6 +12,8 @@
 
 package org.locationtech.jts.shape.random;
 
+import java.util.Random;
+
 import org.locationtech.jts.algorithm.locate.IndexedPointInAreaLocator;
 import org.locationtech.jts.algorithm.locate.PointOnGeometryLocator;
 import org.locationtech.jts.geom.Coordinate;
@@ -34,6 +36,7 @@ public class RandomPointsBuilder
 {
   protected Geometry maskPoly = null;
   private PointOnGeometryLocator extentLocator;
+  private Random random = new Random();
 
   /**
    * Create a shape factory which will create shapes using the default
@@ -55,6 +58,18 @@ public RandomPointsBuilder(GeometryFactory geomFact)
   	super(geomFact);
   }
 
+  /**
+   * Sets the random number generator used to generate point coordinates.
+   * This enables reproducible results by providing a {@link Random}
+   * with a fixed seed.
+   *
+   * @param random the random number generator to use
+   */
+  public void setRandom(Random random)
+  {
+  	this.random = random;
+  }
+
   /**
    * Sets a polygonal mask.
    * 
@@ -99,8 +114,8 @@ protected Coordinate createCoord(double x, double y)
 
   protected Coordinate createRandomCoord(Envelope env)
   {
-    double x = env.getMinX() + env.getWidth() * Math.random();
-    double y = env.getMinY() + env.getHeight() * Math.random();
+    double x = env.getMinX() + env.getWidth() * random.nextDouble();
+    double y = env.getMinY() + env.getHeight() * random.nextDouble();
     return createCoord(x, y);
   }
 

modules/core/src/main/java/org/locationtech/jts/shape/random/RandomPointsInGridBuilder.java

@@ -12,6 +12,8 @@
 
 package org.locationtech.jts.shape.random;
 
+import java.util.Random;
+
 import org.locationtech.jts.geom.Coordinate;
 import org.locationtech.jts.geom.Geometry;
 import org.locationtech.jts.geom.GeometryFactory;
@@ -32,6 +34,7 @@ public class RandomPointsInGridBuilder
 {
 	private boolean isConstrainedToCircle = false;
 	private double gutterFraction = 0;
+	private Random random = new Random();
 
   /**
    * Create a builder which will create shapes using the default
@@ -53,6 +56,18 @@ public RandomPointsInGridBuilder(GeometryFactory geomFact)
   	super(geomFact);
   }
 
+  /**
+   * Sets the random number generator used to generate point coordinates.
+   * This enables reproducible results by providing a {@link Random}
+   * with a fixed seed.
+   *
+   * @param random the random number generator to use
+   */
+  public void setRandom(Random random)
+  {
+  	this.random = random;
+  }
+
   /**
    * Sets whether generated points are constrained to lie
    * within a circle contained within each grid cell.
@@ -126,18 +141,18 @@ private Coordinate randomPointInCell(double orgX, double orgY, double xLen, doub
 
   private Coordinate randomPointInGridCell(double orgX, double orgY, double xLen, double yLen)
   {
-    double x = orgX + xLen * Math.random();
-    double y = orgY + yLen * Math.random();
+    double x = orgX + xLen * random.nextDouble();
+    double y = orgY + yLen * random.nextDouble();
     return createCoord(x, y);
   }
 
-  private static Coordinate randomPointInCircle(double orgX, double orgY, double width, double height)
+  private Coordinate randomPointInCircle(double orgX, double orgY, double width, double height)
   {
   	double centreX = orgX + width/2;
   	double centreY = orgY + height/2;
-  		
-  	double rndAng = 2 * Math.PI * Math.random();
-  	double rndRadius = Math.random();
+
+  	double rndAng = 2 * Math.PI * random.nextDouble();
+  	double rndRadius = random.nextDouble();
     // use square root of radius, since area is proportional to square of radius
     double rndRadius2 = Math.sqrt(rndRadius);
   	double rndX = width/2 * rndRadius2 * Math.cos(rndAng); 

modules/core/src/test/java/org/locationtech/jts/shape/random/RandomPointsBuilderTest.java

@@ -0,0 +1,81 @@
+/*
+ * Copyright (c) 2026 woogi-kim.
+ *
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * and Eclipse Distribution License v. 1.0 which accompanies this distribution.
+ * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v20.html
+ * and the Eclipse Distribution License is available at
+ *
+ * http://www.eclipse.org/org/documents/edl-v10.php.
+ */
+package org.locationtech.jts.shape.random;
+
+import java.util.Random;
+
+import org.locationtech.jts.geom.Envelope;
+import org.locationtech.jts.geom.Geometry;
+
+import junit.textui.TestRunner;
+import test.jts.GeometryTestCase;
+
+/**
+ * Tests {@link RandomPointsBuilder}.
+ *
+ * @author woogi-kim
+ *
+ */
+public class RandomPointsBuilderTest
+extends GeometryTestCase {
+  public static void main(String args[]) {
+    TestRunner.run(RandomPointsBuilderTest.class);
+  }
+
+  public RandomPointsBuilderTest(String name)
+  {
+    super(name);
+  }
+
+  public void testDefault() {
+    RandomPointsBuilder builder = new RandomPointsBuilder(getGeometryFactory());
+    builder.setExtent(new Envelope(0, 10, 0, 10));
+    builder.setNumPoints(10);
+    Geometry result = builder.getGeometry();
+    assertEquals(10, result.getNumGeometries());
+  }
+
+  public void testReproducibleWithSameSeed() {
+    Geometry result1 = createPoints(42, 100);
+    Geometry result2 = createPoints(42, 100);
+    assertTrue(result1.equalsExact(result2));
+  }
+
+  public void testDifferentSeedProducesDifferentResult() {
+    Geometry result1 = createPoints(42, 100);
+    Geometry result2 = createPoints(99, 100);
+    assertFalse(result1.equalsExact(result2));
+  }
+
+  public void testReproducibleWithPolygonalExtent() {
+    Geometry mask = read("POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))");
+    Geometry result1 = createPointsInPolygon(mask, 42, 50);
+    Geometry result2 = createPointsInPolygon(mask, 42, 50);
+    assertTrue(result1.equalsExact(result2));
+  }
+
+  private Geometry createPoints(long seed, int numPts) {
+    RandomPointsBuilder builder = new RandomPointsBuilder(getGeometryFactory());
+    builder.setExtent(new Envelope(0, 10, 0, 10));
+    builder.setNumPoints(numPts);
+    builder.setRandom(new Random(seed));
+    return builder.getGeometry();
+  }
+
+  private Geometry createPointsInPolygon(Geometry mask, long seed, int numPts) {
+    RandomPointsBuilder builder = new RandomPointsBuilder(getGeometryFactory());
+    builder.setExtent(mask);
+    builder.setNumPoints(numPts);
+    builder.setRandom(new Random(seed));
+    return builder.getGeometry();
+  }
+}

modules/core/src/test/java/org/locationtech/jts/shape/random/RandomPointsInGridBuilderTest.java

@@ -0,0 +1,81 @@
+/*
+ * Copyright (c) 2026 woogi-kim.
+ *
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * and Eclipse Distribution License v. 1.0 which accompanies this distribution.
+ * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v20.html
+ * and the Eclipse Distribution License is available at
+ *
+ * http://www.eclipse.org/org/documents/edl-v10.php.
+ */
+package org.locationtech.jts.shape.random;
+
+import java.util.Random;
+
+import org.locationtech.jts.geom.Envelope;
+import org.locationtech.jts.geom.Geometry;
+
+import junit.textui.TestRunner;
+import test.jts.GeometryTestCase;
+
+/**
+ * Tests {@link RandomPointsInGridBuilder}.
+ *
+ * @author woogi-kim
+ *
+ */
+public class RandomPointsInGridBuilderTest
+extends GeometryTestCase {
+  public static void main(String args[]) {
+    TestRunner.run(RandomPointsInGridBuilderTest.class);
+  }
+
+  public RandomPointsInGridBuilderTest(String name)
+  {
+    super(name);
+  }
+
+  public void testDefault() {
+    RandomPointsInGridBuilder builder = new RandomPointsInGridBuilder(getGeometryFactory());
+    builder.setExtent(new Envelope(0, 10, 0, 10));
+    builder.setNumPoints(9);
+    Geometry result = builder.getGeometry();
+    assertEquals(9, result.getNumGeometries());
+  }
+
+  public void testReproducibleWithSameSeed() {
+    Geometry result1 = createGridPoints(42, 25);
+    Geometry result2 = createGridPoints(42, 25);
+    assertTrue(result1.equalsExact(result2));
+  }
+
+  public void testDifferentSeedProducesDifferentResult() {
+    Geometry result1 = createGridPoints(42, 25);
+    Geometry result2 = createGridPoints(99, 25);
+    assertFalse(result1.equalsExact(result2));
+  }
+
+  public void testReproducibleWithConstrainedToCircle() {
+    Geometry result1 = createGridPointsInCircle(42, 25);
+    Geometry result2 = createGridPointsInCircle(42, 25);
+    assertTrue(result1.equalsExact(result2));
+  }
+
+  private Geometry createGridPoints(long seed, int numPts) {
+    RandomPointsInGridBuilder builder = new RandomPointsInGridBuilder(getGeometryFactory());
+    builder.setExtent(new Envelope(0, 10, 0, 10));
+    builder.setNumPoints(numPts);
+    builder.setRandom(new Random(seed));
+    return builder.getGeometry();
+  }
+
+  private Geometry createGridPointsInCircle(long seed, int numPts) {
+    RandomPointsInGridBuilder builder = new RandomPointsInGridBuilder(getGeometryFactory());
+    builder.setExtent(new Envelope(0, 10, 0, 10));
+    builder.setNumPoints(numPts);
+    builder.setConstrainedToCircle(true);
+    builder.setRandom(new Random(seed));
+    return builder.getGeometry();
+  }
+}