Alternative for 5.2

src/main/java/_5/_2/alternative/bill/Bill.java

@@ -0,0 +1,62 @@
+package _5._2.alternative.bill;
+
+import _5._2.alternative.car.CarComponent;
+
+import java.util.LinkedList;
+import java.util.List;
+
+/*
+ * final damit keiner ein BillItem nach draußen gibt
+ * und es später wieder als Argument nimmt.
+ */
+public final class Bill {
+	private List<BillItem> items = new LinkedList<>();
+
+	public double getTotalPrice() {
+		double sum = 0.0;
+		for(BillItem item : this.items) {
+			sum += item.getPrice();
+		}
+		return sum;
+	}
+
+	public boolean add(CarComponent item, double price) {
+		return this.items.add(new BillItem(item, price));
+	}
+
+	@Override
+	public String toString() {
+		StringBuilder sb = new StringBuilder();
+		double total = 0.0;
+		for(BillItem item : this.items) {
+			sb.append(item.toString()).append('\n');
+			total += item.getPrice();
+		}
+		sb.append("Total: ").append(total);
+		return sb.toString();
+	}
+
+	//inner class und private constructor damit eine Instanz nur als Teil einer Rechnung existieren kann.
+	public class BillItem {
+		private final CarComponent item;
+		private final double price;
+
+		private BillItem(CarComponent item, double price) {
+			//assert item != null;
+			this.item = item;
+			this.price = price;
+		}
+
+		public double getPrice() {
+			return this.price;
+		}
+
+		@Override
+		public String toString() {
+			if(this.item.getComponents().isEmpty()) {
+				return this.item.getName() + ": " + this.price;
+			}
+			return this.item.getName() + this.item.getComponents() + ": " + this.price;
+		}
+	}
+}

src/main/java/_5/_2/alternative/bill/BillExample.java

@@ -0,0 +1,18 @@
+package _5._2.alternative.bill;
+
+import _5._2.alternative.car.Motor;
+import _5._2.alternative.car.Seat;
+import _5._2.alternative.car.Wheel;
+
+public class BillExample {
+	public static void main(String[] args) {
+		Bill bill = new Bill();
+		bill.add(new Motor("Rolls Royce (Motor)"), 100000.0);
+		bill.add(new Seat(), 2000.0);
+		bill.add(new Wheel(), 1000.0);
+		bill.add(new Wheel(), 1000.0);
+		bill.add(new Wheel(), 1000.0);
+		bill.add(new Wheel(), 1000.0);
+		System.out.println(bill);
+	}
+}

src/main/java/_5/_2/alternative/car/Car.java

@@ -0,0 +1,58 @@
+package _5._2.alternative.car;
+
+import java.util.HashSet;
+import java.util.Set;
+
+public class Car implements CarComponent {
+	private String name;
+	private final Set<CarComponent> components = new HashSet<>();
+
+	public Car(String name) {
+		this.name = name;
+	}
+
+	@Override
+	public String getName() {
+		return this.name;
+	}
+
+	@Override
+	public Set<CarComponent> getComponents() {
+		return this.components;
+	}
+
+	@Override
+	public String toString() {
+		if(this.components.isEmpty()) {
+			return this.name;
+		}
+		return this.name + ": " + this.components;
+	}
+
+	public abstract static class CarPart implements CarComponent {
+		private String name;
+		private final Set<CarComponent> components = new HashSet<>();
+
+		public CarPart(String name) {
+			this.name = name;
+		}
+
+		@Override
+		public String getName() {
+			return this.name;
+		}
+
+		@Override
+		public Set<CarComponent> getComponents() {
+			return this.components;
+		}
+
+		@Override
+		public String toString() {
+			if(this.components.isEmpty()) {
+				return this.name;
+			}
+			return this.name + ": " + this.components;
+		}
+	}
+}

src/main/java/_5/_2/alternative/car/CarComponent.java

@@ -0,0 +1,16 @@
+package _5._2.alternative.car;
+
+import java.util.Collection;
+
+/*
+ * Ein Interface hat keinen state.
+ * Es kann also auch keine Anforderungen an seinen state stellen.
+ * Um alle geforderten Multiplizitäten sicherzustellen müsste man
+ * sich daher auf jeden der dies implementiert verlassen,
+ * dass er sich an die Vereinbarung hällt.
+ */
+public interface CarComponent {
+	String getName();
+
+	Collection<CarComponent> getComponents();
+}

src/main/java/_5/_2/alternative/car/Motor.java

@@ -0,0 +1,11 @@
+package _5._2.alternative.car;
+
+public class Motor extends Car.CarPart {
+	public Motor() {
+		this("Motor");
+	}
+
+	public Motor(String name) {
+		super(name);
+	}
+}

src/main/java/_5/_2/alternative/car/Seat.java

@@ -0,0 +1,11 @@
+package _5._2.alternative.car;
+
+public class Seat extends Car.CarPart {
+	public Seat() {
+		this("Seat");
+	}
+
+	public Seat(String name) {
+		super(name);
+	}
+}

src/main/java/_5/_2/alternative/car/Wheel.java

@@ -0,0 +1,11 @@
+package _5._2.alternative.car;
+
+public class Wheel extends Car.CarPart {
+	public Wheel() {
+		this("Wheel");
+	}
+
+	public Wheel(String name) {
+		super(name);
+	}
+}