Fix Comparable/Comparator code snippet

04-collections-clean-code/snippets/src/comparators/Car.java

@@ -1,11 +1,21 @@
 package comparators;
 
+import java.util.Objects;
+
 public class Car implements Comparable<Car> {
 
+    private final String vin; // unique identifier
     private int topSpeed;
     private String color;
     private String brand;
 
+    public Car(String vin, int topSpeed, String color, String model) {
+        this.vin = vin;
+        this.topSpeed = topSpeed;
+        this.color = color;
+        this.brand = model;
+    }
+
     public int getTopSpeed() {
         return topSpeed;
     }
@@ -18,24 +28,42 @@ public String getBrand() {
         return brand;
     }
 
-    public Car(int topSpeed, String color, String model) {
-        this.topSpeed = topSpeed;
-        this.color = color;
-        this.brand = model;
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        Car car = (Car) o;
+        return Objects.equals(vin, car.vin);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hashCode(vin);
     }
 
     @Override
     public int compareTo(Car other) {
         // Let's sort the cars by top speed in ascending order.
         // The method returns a negative integer, zero, or a positive integer when this car's top speed
         // is less than, equal to, or greater than the top speed of the specified object.
-        // Integer.compare(other.topSpeed, this.topSpeed);
+
+        // make sure the natural ordering is consistent with equals()
+        if (this.vin.equals(other.vin)) {
+            return 0;
+        } else if (this.topSpeed == other.topSpeed) {
+            return -1; // workaround, but should not return 0 to remain consistent with equals()
+        }
         return Integer.compare(this.topSpeed, other.topSpeed);
     }
 
     @Override
     public String toString() {
-        return "[topSpeed=" + this.topSpeed + ", color=" + this.color + ", model=" + this.brand + "]";
+        return "Car{" +
+            "vin='" + vin + '\'' +
+            ", topSpeed=" + topSpeed +
+            ", color='" + color + '\'' +
+            ", brand='" + brand + '\'' +
+            '}';
     }
 
 }