java-對象的建立

1、考慮用靜態工廠方法來替代構造器

• 靜態工廠與設計模式中的工廠方法模式不一樣
• 與構造器比第一大優點：他們有具體的名稱，而不是類名
• 與構造器比第二大優點：沒必要在每次調用它的時候都建立一個新對象
• 與構造器比第三大優點：它能夠返回原返回類型的任何子類型的對象
• 與構造器比第四大優點：在建立參數化實例時，能夠使代碼變得更加簡潔

舉例以下：

  1 public static Boolean valueof(boolean a){
  2 		return a?Boolean.TRUE:Boolean.FALSE;
  3 	}

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2、服務提供者框架

• 服務接口：提供者實例
• 提供者註冊API：系統用來註冊實現，讓客服端訪問它們
• 服務訪問API：客服端用來獲取服務的實例，是一個靈活的靜態工廠

舉例以下：

  1 public interface Service{
  2 		//service-specific methods go here
  3 	}
  4 	
  5 	public interface Provider{
  6 		Service newService();
  7 	}
  8 	
  9 	public  class Services{
 10 		private Services(){}
 11 		
 12 		private static final Map<String, Provider> providers=new ConcurrentHashMap<String, Provider>();
 13 		public static final String DEFAULT_PROVIDER_NAME="<def>";
 14 		
 15 		//provider registration API
 16 		public static void  registerDefaultProvider(Provider p){
 17 			registerProvider(DEFAULT_PROVIDER_NAME, p);
 18 		}
 19 		public static void registerProvider(String name,Provider p){
 20 			providers.put(name, p);
 21 		}
 22 		
 23 		//service access API
 24 		public static Service newInstance(){
 25 			return newInsance(DEFAULT_PROVIDER_NAME);
 26 		}
 27 		public static Service newInsance(String name){
 28 			Provider provider= providers.get(name);
 29 			if(provider==null){
 30 				throw new IllegalArgumentException("No provider registered with name:"+ name);
 31 			}
 32 			return provider.newService();
 33 		}
 34 	}
 35 

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3、Builder 模式

• 當遇到多個構造器參數時考慮使用構建器
• 與重疊構造器模式、JavaBean模式相比，既能保證像重疊構造器模式那樣安全，又能保證JavaBeans模式那麼好的可讀性，並且也更易於擴展

重疊構造器模式舉例：

  1 public class NutritionFacts
  2 {
  3 	private  int servingSize; //required;
  4 	private  int servings;    //required;
  5 	private int calorier;    //optioned;
  6 	private  int fat;         //optioned;
  7 	private int sodium;      //optioned;
  8 	private  int carbohydrate;//optioned;
  9 	
 10 	public NutritionFacts(int servingSize,int servings){
 11 		this(servingSize, servingSize, 0);
 12 	}
 13 	
 14 	public NutritionFacts(int servingSize,int servings,int calorier){
 15 		this(servingSize, servings, calorier,0);
 16 	}
 17 	
 18 	public NutritionFacts(int servingSize,int servings,int calorier,int fat){
 19 		this(servingSize, servings, calorier,fat,0,0);
 20 	}
 21 	
 22 	public NutritionFacts(int servingSize,int servings,int calorier,int fat,int sodium){
 23 		this(servingSize, servings, calorier,fat, sodium,0);
 24 	}
 25 	
 26 	public NutritionFacts(int servingSize,int servings,int calorier,int fat,int sodium,int carbohydrate){
 27 		this.servingSize=servingSize;
 28 		this.servings=servings;
 29 		this.calorier=calorier;
 30 		this.fat=fat;
 31 		this.sodium=sodium;
 32 		this.carbohydrate=carbohydrate;
 33 	}
 34 }
 35 

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javaBeans模式舉例：

  1 public class NutritionFacts
  2 {
  3 	private  int servingSize; //required;
  4 	private  int servings;    //required;
  5 	private int calorier;    //optioned;
  6 	private  int fat;         //optioned;
  7 	private int sodium;      //optioned;
  8 	private  int carbohydrate;//optioned;
  9 	
 10 	public NutritionFacts(){}
 11 
 12 	public int getServingSize()
 13 	{
 14 		return servingSize;
 15 	}
 16 
 17 	public void setServingSize(int servingSize)
 18 	{
 19 		this.servingSize = servingSize;
 20 	}
 21 
 22 	public int getServings()
 23 	{
 24 		return servings;
 25 	}
 26 
 27 	public void setServings(int servings)
 28 	{
 29 		this.servings = servings;
 30 	}
 31 
 32 	public int getCalorier()
 33 	{
 34 		return calorier;
 35 	}
 36 
 37 	public void setCalorier(int calorier)
 38 	{
 39 		this.calorier = calorier;
 40 	}
 41 
 42 	public int getFat()
 43 	{
 44 		return fat;
 45 	}
 46 
 47 	public void setFat(int fat)
 48 	{
 49 		this.fat = fat;
 50 	}
 51 
 52 	public int getSodium()
 53 	{
 54 		return sodium;
 55 	}
 56 
 57 	public void setSodium(int sodium)
 58 	{
 59 		this.sodium = sodium;
 60 	}
 61 
 62 	public int getCarbohydrate()
 63 	{
 64 		return carbohydrate;
 65 	}
 66 
 67 	public void setCarbohydrate(int carbohydrate)
 68 	{
 69 		this.carbohydrate = carbohydrate;
 70 	}
 71 	
 72 	
 73 }
 74 

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Builder Pattern舉例：

  1 public class NutritionFacts
  2 {
  3 	private  int servingSize; //required;
  4 	private  int servings;    //required;
  5 	private  int calorier;    //optioned;
  6 	private   int fat;         //optioned;
  7 	private int sodium;      //optioned;
  8 	private   int carbohydrate;//optioned;
  9 	
 10 	public static class Builder{
 11 		private int servingSize;
 12 		private int servings;
 13 		
 14 		private int calorier=0;
 15 		private int fat=0;
 16 		private int carbohydrate=0;
 17 		private int sodium=0;
 18 		
 19 		public Builder(int servingSize,int servings){
 20 			this.servingSize=servingSize;
 21 			this.servings=servings;
 22 		}
 23 		
 24 		public Builder calories(int val){
 25 			calorier=val;
 26 			return this;
 27 		}
 28 		public Builder fat(int val){
 29 			fat=val;
 30 			return this;
 31 		}
 32 		public Builder carhohydrate(int val){
 33 			carbohydrate=val;
 34 			return this;
 35 		}
 36 		public Builder sodium(int val){
 37 			sodium=val;
 38 			return this;
 39 		}
 40 		
 41 		public NutritionFacts build(){
 42 			return new NutritionFacts(this);
 43 		}
 44 	}
 45 	
 46 	private NutritionFacts(Builder builder){
 47 		servingSize=builder.servingSize;
 48 		servings=builder.servings;
 49 		calorier=builder.calorier;
 50 		fat=builder.fat;
 51 		sodium=builder.sodium;
 52 		carbohydrate=builder.carbohydrate;
 53 	}
 54 	
 55 	public static void main(String[] args)
 56 	{
 57 		NutritionFacts coca=new NutritionFacts.Builder(240, 8).calories(100).sodium(35).carhohydrate(27).build();
 58 		
 59 		System.out.println(coca.servingSize+";"+coca.servings+";"+coca.calorier+";"+coca.fat+";"+coca.sodium+";"+coca.carbohydrate);
 60 	}
 61 }
 62 

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