第一章.良好应用程序基石(3)

客户又通知我们，他的Guitars库中有很多相同属性的吉他，但是可能售价上不同。

现在，我们要实现的是，怎样返回库中能匹配所有属性的Guitar，并列出来。

更新Inventory.java中的search()方法：

public List search(Guitar searchGuitar){
        List matchingGuitars = new LinkedList();
        for(Iterator i = guitars.iterator(); i.hasNext();){
            Guitar guitar = (Guitar) i.next();
            
            if(searchGuitar.getBuilder() != guitar.getBuilder())
                    continue;
            
            String model = searchGuitar.getModel().toLowerCase();
            if((model != null) && (!model.equals("")) && 
                    (!model.equals(guitar.getModel().toLowerCase())))
                    continue;
            
            if(searchGuitar.getType() != guitar.getType())
                    continue;
            
            if(searchGuitar.getBackWood() != guitar.getBackWood())
                    continue;
            
            if(searchGuitar.getTopWood() != guitar.getTopWood())
                    continue;
            
            matchingGuitars.add(guitar);
        }
        
        return matchingGuitars;
    }

更新FindGuitarTester.java:

package com.headfirst.guitar;

import java.util.Iterator;
import java.util.List;

public class FindGuitarTester {
    public static void main(String[] args){
        Inventory inventory = new Inventory();
        initializeInventory(inventory);
        
        Guitar whatErinLikes = new Guitar("", 0, Builder.FENDER, "Stratocastor", 
                Type.ELECTRIC, Wood.ALDER, Wood.ALDER);
        
        List matchingGuitars = inventory.search(whatErinLikes);
        if(!matchingGuitars.isEmpty()){
            System.out.println("Erin, you might like these guitars: "); 
            for(Iterator i = matchingGuitars.iterator(); i.hasNext();){
                Guitar guitar = (Guitar) i.next();
                System.out.println("We have a " +
                guitar.getBuilder() + " " + guitar.getModel() + " " + 
                guitar.getType() + " guitar:\n " + 
                guitar.getBackWood() + " back and sides,\n " +
                guitar.getTopWood() + " top.\nYou can have it for only $" + 
                guitar.getPrice() + "!");
            }
        }else{
            System.out.println("Sorry, Erin, we have nothing for you.");
        }
    }
    
    private static void initializeInventory(Inventory inventory){
        inventory.addGuitar("V95693", 1499.95, Builder.FENDER, "Stratocastor", Type.ELECTRIC, Wood.ALDER, Wood.ALDER);
        inventory.addGuitar("B1234", 1600.35, Builder.FENDER, "Stratocastor", Type.ELECTRIC, Wood.ALDER, Wood.ALDER);
    }
}

通过以上的修改，我们完成了步骤一：确认你的软件做客户要它做的事。

我们开始步骤二：运用基本的OO原则来增加软件的灵活性。

1.对象应该做其名称所指之事。

2.每个对象应该代表单一概念。

3.未使用的特性是无用的赠品。

4.任何时候，看到重复的代码，就找个地方进行封装。

Inventory.java中的search()方法，需要改进的地方就是，用户不必传入一个Guitar对象，因为Guitar里的变量不全是用来搜索的，比如价格、序号用户是不知道的。

所以，我们要从Guitar类中分割出来一个类，专门用来存储用户搜索数据。

项目架构：

Guitar.java：

package com.headfirst.guitar;

public class Guitar {
    private String serialNumber;
    private double price;
    private GuitarSpec guitarSpec;
    
    public Guitar(String serialNumber, double price, GuitarSpec guitarSpec){
        this.serialNumber = serialNumber;
        this.price = price;
        this.guitarSpec = guitarSpec;
    }
    
    public String getSerialNumber(){
        return serialNumber;
    }
    public double getPrice(){
        return price;
    }
    public void setPrice(float newPrice){
        this.price = newPrice;
    }
    public GuitarSpec getGuitarSpec(){
        return guitarSpec;
    }
}

GuitarSpec.java：

package com.headfirst.guitar;

public class GuitarSpec {
    Builder builder;
    String model;
    Type type;
    Wood backWood;
    Wood topWood;
    
    public GuitarSpec(Builder builder, String model, Type type, Wood backWood, Wood topWood){
        this.builder = builder;
        this.model = model;
        this.type = type;
        this.backWood = backWood;
        this.topWood = topWood;
    }
    
    public Builder getBuilder(){
        return this.builder;
    }
    
    public String getModel(){
        return this.model;
    }
    
    public Type getType(){
        return this.type;
    }
    
    public Wood getBackWood(){
        return this.backWood;
    }
    
    public Wood getTopWood(){
        return this.topWood;
    }
}

Inventory.java 修改：

package com.headfirst.guitar;

import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;

public class Inventory {
    
    private List guitars;
    
    public Inventory(){
        guitars = new LinkedList();
    }
    
    public void addGuitar(String serialNumber, double price, GuitarSpec guitarSpec){
        Guitar guitar = new Guitar(serialNumber, price, guitarSpec);
        guitars.add(guitar);
    }
    
    public Guitar getGuitar(String serialNumber){
        for(Iterator i = guitars.iterator(); i.hasNext();){
            Guitar guitar = (Guitar) i.next();
            if(guitar.getSerialNumber().equals(serialNumber)){
                return guitar;
            }
        }
        
        return null;
    }
    
    public List search(GuitarSpec searchGuitar){
        List matchingGuitars = new LinkedList();
        for(Iterator i = guitars.iterator(); i.hasNext();){
            Guitar guitar = (Guitar) i.next();
            GuitarSpec guitarSpec = guitar.getGuitarSpec();
            
            if(searchGuitar.getBuilder() != guitarSpec.getBuilder())
                    continue;
            
            String model = searchGuitar.getModel().toLowerCase();
            if((model != null) && (!model.equals("")) && 
                    (!model.equals(guitarSpec.getModel().toLowerCase())))
                    continue;
            
            if(searchGuitar.getType() != guitarSpec.getType())
                    continue;
            
            if(searchGuitar.getBackWood() != guitarSpec.getBackWood())
                    continue;
            
            if(searchGuitar.getTopWood() != guitarSpec.getTopWood())
                    continue;
            
            matchingGuitars.add(guitar);
        }
        
        return matchingGuitars;
    }
}

FindGuitarTester.java修改：

package com.headfirst.guitar;

import java.util.Iterator;
import java.util.List;

public class FindGuitarTester {
    public static void main(String[] args){
        Inventory inventory = new Inventory();
        initializeInventory(inventory);
        
        GuitarSpec whatErinLikes = new GuitarSpec(Builder.FENDER, "Stratocastor", Type.ELECTRIC, Wood.ALDER, Wood.ALDER);
        
        List matchingGuitars = inventory.search(whatErinLikes);
        if(!matchingGuitars.isEmpty()){
            System.out.println("Erin, you might like these guitars: "); 
            for(Iterator i = matchingGuitars.iterator(); i.hasNext();){
                Guitar guitar = (Guitar) i.next();
                GuitarSpec guitarSpec = guitar.getGuitarSpec();
                System.out.println("We have a " +
                guitarSpec.getBuilder() + " " + guitarSpec.getModel() + " " + 
                guitarSpec.getType() + " guitar:\n " + 
                guitarSpec.getBackWood() + " back and sides,\n " +
                guitarSpec.getTopWood() + " top.\nYou can have it for only $" + 
                guitar.getPrice() + "!");
            }
        }else{
            System.out.println("Sorry, Erin, we have nothing for you.");
        }
    }
    
    private static void initializeInventory(Inventory inventory){
        GuitarSpec guitarSpec1 = new GuitarSpec(Builder.FENDER, "Stratocastor", Type.ELECTRIC, Wood.ALDER, Wood.ALDER);
        inventory.addGuitar("V95693", 1499.95, guitarSpec1);
        inventory.addGuitar("B1234", 1600.35, guitarSpec1);
    }
}

我们把Guitar类中给用户搜索用的变量，重新构造一个新的类GuitarSpec。

这样Guitar类的功能就很单一了，就是存储Guitar对象，GuitarSpec类则是为了提供给用户搜索相关信息的。

运行结果：