Java设计模式(4) -- 模板方法-优快云博客

本文链接：https://blog.youkuaiyun.com/gtuu0123/article/details/4458800

本文详细介绍了模板方法设计模式的概念及应用方式，通过一个具体的文档处理应用案例展示了如何定义算法骨架，并允许子类重新定义算法步骤而不改变整体结构。

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Template Method

英文简要描述

Intent
Define the skeleton of an algorithm in an operation, deferring some steps to subclasses.
Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.

How to
AbstractClass
defines abstract primitive operations that concrete subclasses define to implement steps of an algorithm.
implements a template method defining the skeleton of an algorithm. The template method calls primitive operations as well as operations defined in AbstractClass or those of other objects.
ConcreteClass
implements the primitive operations to carry out subclass-specific steps of the algorithm.

Known cases
A lot

UML

模板方法通常和工厂方法一起使用，以下是样例:

public abstract class Application { private List docs = new ArrayList(); public Document openDocument(String path) { Document doc = null; if (isDocumentExist(path)) { doc = newDocument(); } else { doc = readDocument(path); } appendDocument(doc); check(doc); return doc; } private boolean isDocumentExist(String path) { // check if the document exists // ... return true; } private void appendDocument(Document doc) { docs.add(doc); } protected abstract Document newDocument(); // factory method protected abstract Document readDocument(String path); //primitive method protected void check(Document doc) { // hook method // do thing } } public class ExcelApplication extends Application { protected Document newDocument() { return new ExcelDocument(); } protected Document readDocument(String path) { System.out.println("Read Excel Document"); return null; } protected void check(Document doc) { System.out.println("Check Excel Document"); } } public class WordApplication extends Application { protected Document newDocument() { return new WordDocument(); } protected Document readDocument(String path) { System.out.println("Read Word Document"); return null; } } public interface Document { public void show(); } public class ExcelDocument implements Document { public void show() { System.out.println("Show Excel Document"); } } public class WordDocument implements Document { public void show() { System.out.println("Show Word Document"); } } public class TestTemplateMethod { public static void main(String[] args) { Application app = null; if (args[0].equals("Word")) { app = new WordApplication(); } else if (args[0].equals("Excel")) { app = new ExcelApplication(); } else { throw new RuntimeException("Unsupport type"); } Document doc = app.openDocument("Path"); doc.show(); } }

上例的uml