模板方法模式(template method pattern) 详细解释
本文地址: http://blog.csdn.net/caroline_wendy
模板方法模式(template method pattern): 在一个方法中定义一个算法的骨架, 而将一些步骤延迟到子类中.
模板方法使得子类能够在不改变算法结构的情况下, 又一次定义算法中的某些步骤.
模板方法能够进行挂钩(hook), 钩子(hook)是一种被声明在抽象类中的方法, 但仅仅有空的或者默认的实现.
钩子的存在, 能够让子类有能力对算法的不同点进行挂钩.
抽象类的框架:
/**
* @time 2014年6月18日
*/
package template_method;
/**
* @author C.L.Wang
*
*/
public abstract class AbstractClass {
final void templateMethod() {
primitiveOperation1();
primitiveOperation2();
concreteOperation();
hook();
}
abstract void primitiveOperation1();
abstract void primitiveOperation2();
final void concreteOperation() {
}
void hook() {}
}
面向对象原则:
好莱坞原则: 别调用我们, 我们会调用你.
详细方法:
1. 抽象类(abstract class), 包括模板方法(template method), 抽象操作(abstract operation),
详细操作(concrete operation), 和钩子(hook).
/**
* @time 2014年6月18日
*/
package template_method;
/**
* @author C.L.Wang
*
*/
public abstract class CaffeineBeverage {
final void prepareRecipe() { //模板方法
boilWater();
brew();
pourInCup();
if(customerWantsCondiments()) {
addCondiments();
}
}
abstract void brew(); //抽象操作
abstract void addCondiments();
void boilWater() { //详细操作
System.out.println("Boiling water");
}
void pourInCup() {
System.out.println("Pouring into cup");
}
boolean customerWantsCondiments() { //钩子
return true;
}
}
2. 详细类(concrete class), 继承(extend) 抽象类(abstract class).
/**
* @time 2014年6月18日
*/
package template_method;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
/**
* @author C.L.Wang
*
*/
public class CoffeeWithHook extends CaffeineBeverage {
/* (non-Javadoc)
* @see template_method.CaffeineBeverage#brew()
*/
@Override
void brew() {
// TODO Auto-generated method stub
System.out.println("Dripping Coffee through filter");
}
/* (non-Javadoc)
* @see template_method.CaffeineBeverage#addCondiments()
*/
@Override
void addCondiments() {
// TODO Auto-generated method stub
System.out.println("Adding Sugar and Milk");
}
public boolean customerWantsCondiments() { //钩子
String answer = getUserInput();
if (answer.toLowerCase().startsWith("y")) {
return true;
} else {
return false;
}
}
private String getUserInput() {
String answer = null;
System.out.println("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.out.println("IO error trying to read your answer");
}
if (answer == null) {
return "no";
}
return answer;
}
}
/**
* @time 2014年6月18日
*/
package template_method;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
/**
* @author C.L.Wang
*
*/
public class TeaWithHook extends CaffeineBeverage {
/* (non-Javadoc)
* @see template_method.CaffeineBeverage#brew()
*/
@Override
void brew() {
// TODO Auto-generated method stub
System.out.println("Steeping the tea");
}
/* (non-Javadoc)
* @see template_method.CaffeineBeverage#addCondiments()
*/
@Override
void addCondiments() {
// TODO Auto-generated method stub
System.out.println("Adding Lemon");
}
public boolean customerWantsCondiments() {
String answer = getUserInput();
if (answer.toLowerCase().startsWith("y")) {
return true;
} else {
return false;
}
}
private String getUserInput() {
String answer = null;
System.out.println("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.out.println("IO error trying to read your answer");
}
if (answer == null) {
return "no";
}
return answer;
}
}
3. 測试类, 包括钩子(hook)操作.
/**
* @time 2014年6月18日
*/
package template_method;
/**
* @author C.L.Wang
*
*/
public class BeverageTestDrive {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
TeaWithHook teaHook = new TeaWithHook();
CoffeeWithHook coffeeHook = new CoffeeWithHook();
System.out.println("
Making tea...");
teaHook.prepareRecipe();
System.out.println("
Making coffee...");
coffeeHook.prepareRecipe();
}
}
4. 输出:
Making tea... Boiling water Steeping the tea Pouring into cup Would you like lemon with your tea (y/n)?y Adding Lemon Making coffee... Boiling water Dripping Coffee through filter Pouring into cup Would you like milk and sugar with your coffee (y/n)? n
