面向对象五大原则_基石_开闭原则

为什么没有说是面向对象6大原则，为什么没有将开闭原则包含进去？  

开闭原则是最基础的一个原则，前面5个原则就是它的详细形态，开闭原则才是他们的接口。

IBook作为一个接口。里面有三个方法，而小说NovelBook是一个详细的实现类，是全部小说的总称，BookStore指的是书店。

public interface IBook {
 public String getName();
 public int getPrice();
 public String getAuthor();
}

public class NovelBook implements IBook {
 private String name;
 private int price;
 private String autor;
 
 public NovelBook(String name,int price,String autor){
  this.name=name;
  this.price=price;
  this.autor=autor;
 }
 
 public String getAuthor() {
  return this.autor;
 }

 public String getName() {
  return this.name;
 }

 public int getPrice() {
  return this.price;
 }
}

public class Store {

 private final static ArrayList<IBook> booklist = new ArrayList<IBook>();

 static { // 静态模块载入数据，实际项目一般由持久层完毕
  booklist.add(new NovelBook("巴黎圣母院", 3200, "雨果"));
  booklist.add(new NovelBook("悲慘世界", 5600, "雨果"));
  booklist.add(new NovelBook("天龙八部", 4800, "金庸"));
  booklist.add(new NovelBook("挪威的森林", 2200, "村上春树"));
 }

 public static void main(String[] args) {
  NumberFormat format = NumberFormat.getCurrencyInstance();
  format.setMaximumFractionDigits(2);

  System.out.println("-------------书店卖出去的书籍记录例如以下---------------");
  for (IBook book : booklist) {
   System.out.println("书籍名称:" + book.getName() + "\t书籍作者:"
     + book.getAuthor() + "\t书籍价格:"
     + format.format(book.getPrice() / 100.0) + "元");
  }
 }
}

public class OffNovelBook extends NovelBook {
 
 public OffNovelBook(String name, int price, String autor) {
  super(name, price, autor);
 }
 @Override
 public int getPrice() {
  int price=super.getPrice();
  int oprice=0;
  if(price>4000){
   oprice= price*90/100;
  }else{
   oprice= price*80/100;
  }
  return oprice;
 }
}

static { // 静态模块载入数据。实际项目一般由持久层完毕
  booklist.add(new NovelBook("巴黎圣母院", 3200, "雨果"));
  booklist.add(new NovelBook("悲慘世界", 5600, "雨果"));
  booklist.add(new NovelBook("天龙八部", 4800, "金庸"));
  booklist.add(new NovelBook("挪威的森林", 2200, "村上春树"));
  booklist.add(new OffNovelBook("唐诗三百首", 4500, "谁写的"));
 }

public interface IComputerBook extends IBook {
 public String getScope();
}

public class ComputerBook implements IComputerBook {
 private String name;
 private int price;
 private String autor;
 private String scope;
 
 public ComputerBook(String name, int price, String autor, String scope) {
  this.name = name;
  this.price = price;
  this.autor = autor;
  this.scope = scope;
 }

 public String getScope() {
  return this.scope;
 }

 public String getAuthor() {
  return this.autor;
 }

 public String getName() {
  return this.name;
 }

 public int getPrice() {
  return this.price;
 }
}

static { // 静态模块载入数据，实际项目一般由持久层完毕
  booklist.add(new NovelBook("巴黎圣母院", 3200, "雨果"));
  booklist.add(new NovelBook("悲慘世界", 5600, "雨果"));
  booklist.add(new NovelBook("天龙八部", 4800, "金庸"));
  booklist.add(new NovelBook("挪威的森林", 2200, "村上春树"));
  booklist.add(new OffNovelBook("下架的书", 4500, "谁写的"));
  booklist.add(new ComputerBook("大数据入门", 8500, "李老师", "大数据"));
  booklist.add(new ComputerBook("嵌入式精髓", 2600, "吴老师", "嵌入式"));
 }

參考书籍《设计模式之禅》

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