Changed shape to abstract class to reduce code duplication

src/shapes/Ellipse.java

@@ -1,10 +1,8 @@
 package shapes;
 
-public class Ellipse implements Shape {
+public class Ellipse extends Shape {
   private final double a;
   private final double b;
-  private final double weight;
-  private final double length;
   private final double rotation;
   private final Vector position;
 
@@ -15,7 +13,7 @@ public class Ellipse implements Shape {
     this.rotation = rotation;
     this.position = position;
     // Approximation of length.
-    this.length = 2 * Math.PI * Math.sqrt((this.a * this.a + this.b * this.b) / 2);
+    this.length = 2 * Math.PI * Math.sqrt((a * a + b * b) / 2);
   }
 
   public Ellipse(double a, double b, Vector position) {
@@ -58,14 +56,4 @@ public class Ellipse implements Shape {
   public Shape translate(Vector vector) {
     return new Ellipse(a, b, weight, rotation, position.add(vector));
   }
-
-  @Override
-  public double getWeight() {
-    return weight;
-  }
-
-  @Override
-  public double getLength() {
-    return length;
-  }
 }

src/shapes/Line.java

@@ -1,12 +1,8 @@
 package shapes;
 
-public class Line implements Shape {
+public class Line extends Shape {
   private final Vector a;
   private final Vector b;
-  private final double weight;
-
-  // Storing the length to save on repeat calculations.
-  private final double length;
 
   public static final double DEFAULT_WEIGHT = 100;
 
@@ -102,16 +98,6 @@ public class Line implements Shape {
     return new Line(getX1(), getY1(), getX2(), y2);
   }
 
-  @Override
-  public double getWeight() {
-    return weight;
-  }
-
-  @Override
-  public double getLength() {
-    return length;
-  }
-
   public Line setWeight(double weight) {
     return new Line(getX1(), getY1(), getX2(), getY2(), weight);
   }

src/shapes/Shape.java

@@ -1,11 +1,20 @@
 package shapes;
 
-public interface Shape {
-  float nextX(double drawingProgress);
-  float nextY(double drawingProgress);
-  Shape rotate(double theta);
-  Shape scale(double factor);
-  Shape translate(Vector vector);
-  double getWeight();
-  double getLength();
+public abstract class Shape {
+  protected double weight;
+  protected double length;
+
+  public abstract float nextX(double drawingProgress);
+  public abstract float nextY(double drawingProgress);
+  public abstract Shape rotate(double theta);
+  public abstract Shape scale(double factor);
+  public abstract Shape translate(Vector vector);
+
+  public double getWeight() {
+    return weight;
+  }
+
+  public double getLength() {
+    return length;
+  }
 }