- 成分不是 IS-A 三明治；
- 最好将原料价格外部化，以使其灵活变化；
- 最好在运行时根据其成分生成三明治描述，而不是在类级别对其进行硬编码；
- 配料应该对三明治一无所知；
所以，我会提供以下解决方案：
package com;
public enum Ingredient {
CHEESE, TOMATO, LETTUCE, BACON, BREAD, MEATBALL, ITALIAN_SAUCE;
private final String description;
Ingredient() {
description = toString().toLowerCase();
}
Ingredient(String description) {
this.description = description;
}
public String getDescription() {
return description;
}
}
package com;
import static com.Ingredient.*;
import java.util.*;
import static java.util.Arrays.asList;
public enum SandwitchType {
BLT(
asList(TOMATO, LETTUCE, BACON, BREAD),
1 , 1, 1 , 1
),
SUB(
asList(MEATBALL, CHEESE, ITALIAN_SAUCE, BREAD),
1 , 1 , 1 , 1
);
private final Map<Ingredient, Integer> ingredients = new EnumMap<Ingredient, Integer>(Ingredient.class);
private final Map<Ingredient, Integer> ingredientsView = Collections.unmodifiableMap(ingredients);
SandwitchType(Collection<Ingredient> ingredients, int ... unitsNumber) {
int i = -1;
for (Ingredient ingredient : ingredients) {
if (++i >= unitsNumber.length) {
throw new IllegalArgumentException(String.format("Can't create sandwitch %s. Reason: given ingedients "
+ "and their units number are inconsistent (%d ingredients, %d units number)",
this, ingredients.size(), unitsNumber.length));
}
this.ingredients.put(ingredient, unitsNumber[i]);
}
}
public Map<Ingredient, Integer> getIngredients() {
return ingredientsView;
}
public String getDescription() {
StringBuilder result = new StringBuilder();
for (Ingredient ingredient : ingredients.keySet()) {
result.append(ingredient.getDescription()).append(", ");
}
if (result.length() > 1) {
result.setLength(result.length() - 2);
}
return result.toString();
}
}
package com;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
public class PriceList {
private static final int PRECISION = 2;
private final ConcurrentMap<Ingredient, Double> prices = new ConcurrentHashMap<Ingredient, Double>();
public double getPrice(SandwitchType sandwitchType) {
double result = 0;
for (Map.Entry<Ingredient, Integer> entry : sandwitchType.getIngredients().entrySet()) {
Double price = prices.get(entry.getKey());
if (price == null) {
throw new IllegalStateException(String.format("Can't calculate price for sandwitch type %s. Reason: "
+ "no price is defined for ingredient %s. Registered ingredient prices: %s",
sandwitchType, entry.getKey(), prices));
}
result += price * entry.getValue();
}
return round(result);
}
public void setIngredientPrice(Ingredient ingredient, double price) {
prices.put(ingredient, round(price));
}
private static double round(double d) {
double multiplier = Math.pow(10, PRECISION);
return Math.floor(d * multiplier + 0.5) / multiplier;
}
}
package com;
import java.util.Map;
import java.util.EnumMap;
public class Dispenser {
private final Map<Ingredient, Integer> availableIngredients = new EnumMap<Ingredient, Integer>(Ingredient.class);
public String buySandwitch(SandwitchType sandwitchType) {
StringBuilder result = new StringBuilder();
synchronized (availableIngredients) {
Map<Ingredient, Integer> buffer = new EnumMap<Ingredient, Integer>(availableIngredients);
for (Map.Entry<Ingredient, Integer> entry : sandwitchType.getIngredients().entrySet()) {
Integer currentNumber = buffer.get(entry.getKey());
if (currentNumber == null || currentNumber < entry.getValue()) {
result.append(String.format("not enough %s (required %d, available %d), ",
entry.getKey().getDescription(), entry.getValue(), currentNumber == null ? 0 : currentNumber));
continue;
}
buffer.put(entry.getKey(), currentNumber - entry.getValue());
}
if (result.length() <= 0) {
availableIngredients.clear();
availableIngredients.putAll(buffer);
return "";
}
}
if (result.length() > 1) {
result.setLength(result.length() - 2);
}
return result.toString();
}
public void load(Ingredient ingredient, int unitsNumber) {
synchronized (availableIngredients) {
Integer currentNumber = availableIngredients.get(ingredient);
if (currentNumber == null) {
availableIngredients.put(ingredient, unitsNumber);
return;
}
availableIngredients.put(ingredient, currentNumber + unitsNumber);
}
}
}
package com;
public class StartClass {
public static void main(String[] args) {
Dispenser dispenser = new Dispenser();
for (Ingredient ingredient : Ingredient.values()) {
dispenser.load(ingredient, 10);
}
PriceList priceList = loadPrices();
while (true) {
for (SandwitchType sandwitchType : SandwitchType.values()) {
System.out.printf("About to buy %s sandwitch. Price is %f...",
sandwitchType, priceList.getPrice(sandwitchType));
String rejectReason = dispenser.buySandwitch(sandwitchType);
if (!rejectReason.isEmpty()) {
System.out.println(" Failed: " + rejectReason);
return;
}
System.out.println(" Done");
}
}
}
private static PriceList loadPrices() {
PriceList priceList = new PriceList();
double i = 0.1;
for (Ingredient ingredient : Ingredient.values()) {
priceList.setIngredientPrice(ingredient, i);
i *= 2;
}
return priceList;
}
}