设计模式――模板方法模式（Template Method Pattern）

// CaffeineBeverage.java
public abstract class CaffeineBeverage {

final void prepareRecipe() {
boilWater();
brew();
pourInCup();
addCondiments();
}

abstract void brew();

abstract void addCondiments();

void boilWater() {
System.out.println("Boiling water");
}

void pourInCup() {
System.out.println("Pouring into cup");
}
}

// CaffeineBeverageWithHook.java
public abstract class CaffeineBeverageWithHook {

void prepareRecipe() {
boilWater();
brew();
pourInCup();
if (customerWantsCondiments()) {
addCondiments();
}
}

abstract void brew();

abstract void addCondiments();

void boilWater() {
System.out.println("Boiling water");
}

void pourInCup() {
System.out.println("Pouring into cup");
}

boolean customerWantsCondiments() {
return true;
}
}

// Coffee.java
public class Coffee extends CaffeineBeverage {
public void brew() {
System.out.println("Dripping Coffee through filter");
}
public void addCondiments() {
System.out.println("Adding Sugar and Milk");
}
}

// CoffeeWithHook.java
public class CoffeeWithHook extends CaffeineBeverageWithHook {

public void brew() {
System.out.println("Dripping Coffee through filter");
}

public void addCondiments() {
System.out.println("Adding Sugar and Milk");
}

public boolean customerWantsCondiments() {
String answer = getUserInput();
if (answer.toLowerCase().startsWith("y")) {
return true;
} else {
return false;
}
}

private String getUserInput() {
String answer = null;
System.out.print("Would you like milk and sugar with your coffee (y/n)? ");
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
try {
answer = in.readLine();
} catch (IOException ioe) {
System.err.println("IO error trying to read your answer");
}
if (answer == null) {
return "no";
}
return answer;
}
}

// Tea.java
public class Tea extends CaffeineBeverage {
public void brew() {
System.out.println("Steeping the tea");
}
public void addCondiments() {
System.out.println("Adding Lemon");
}
}

// TeaWithHook.java
public class TeaWithHook extends CaffeineBeverageWithHook {

public void brew() {
System.out.println("Steeping the tea");
}

public void addCondiments() {
System.out.println("Adding Lemon");
}

public boolean customerWantsCondiments() {
String answer = getUserInput();
if (answer.toLowerCase().startsWith("y")) {
return true;
} else {
return false;
}
}

private String getUserInput() {
// get the user's response
String answer = null;
System.out.print("Would you like lemon with your tea (y/n)? ");
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
try {
answer = in.readLine();
} catch (IOException ioe) {
System.err.println("IO error trying to read your answer");
}
if (answer == null) {
return "no";
}
return answer;
}
}

// BeverageTestDrive.java
public class BeverageTestDrive {
public static void main(String[] args) {

Tea tea = new Tea();
Coffee coffee = new Coffee();

System.out.println("\nMaking tea...");
tea.prepareRecipe();

System.out.println("\nMaking coffee...");
coffee.prepareRecipe();

TeaWithHook teaHook = new TeaWithHook();
CoffeeWithHook coffeeHook = new CoffeeWithHook();

System.out.println("\nMaking tea...");
teaHook.prepareRecipe();

System.out.println("\nMaking coffee...");
coffeeHook.prepareRecipe();
}
}