第2条：遇到多个构造器参数时要考虑用构建器-优快云博客

重叠构造器模式可行，但是当有许多参数的时候，客户端代码会难以编写，并且仍然较难以阅读。--他的前提是，有很多种不同的构造器情况，也就是很多构造器参数不同，或者说（很多参数可选，因为很多参数有默认值）。
错误示例：

 
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 // Telescoping constructor pattern - does not scale well! - Pages 11-12 
  
 publicclassNutritionFacts { 
 privatefinalintservingSize;// (mL)required 
 privatefinalintservings;// (per container) required 
 privatefinalintcalories;// optional 
 privatefinalintfat;// (g) optional 
 privatefinalintsodium;// (mg)optional 
 privatefinalintcarbohydrate;// (g) optional 
  
 publicNutritionFacts(intservingSize,intservings) { 
 this(servingSize, servings,0); 
 } 
  
 publicNutritionFacts(intservingSize,intservings, 
 intcalories) { 
 this(servingSize, servings, calories,0); 
 } 
  
 publicNutritionFacts(intservingSize,intservings, 
 intcalories,intfat) { 
 this(servingSize, servings, calories, fat,0); 
 } 
  
 publicNutritionFacts(intservingSize,intservings, 
 intcalories,intfat,intsodium) { 
 this(servingSize, servings, calories, fat, sodium,0); 
 } 
  
 publicNutritionFacts(intservingSize,intservings, 
 intcalories,intfat,intsodium,intcarbohydrate) { 
 this.servingSize= servingSize; 
 this.servings = servings; 
 this.calories = calories; 
 this.fat= fat; 
 this.sodium = sodium; 
 this.carbohydrate = carbohydrate; 
 } 
  
 publicstaticvoidmain(String[] args) { 
 NutritionFacts cocaCola = 
 newNutritionFacts(240,8,100,0,35,27); 
 } 
 } 

替代方法：使用JavaBeans模式

 
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 // JavaBeans Pattern - allows inconsistency, mandates mutability - Pages 12-13 
  
 publicclassNutritionFacts { 
 // Parameters initialized to default values (if any) 
 privateintservingSize= -1;// Required; no default value 
 privateintservings = -1;// " " "" 
 privateintcalories =0; 
 privateintfat=0; 
 privateintsodium =0; 
 privateintcarbohydrate =0; 
  
 publicNutritionFacts() { } 
  
 // Setters 
 publicvoidsetServingSize(intval){ servingSize = val; } 
 publicvoidsetServings(intval) { servings = val; } 
 publicvoidsetCalories(intval) { calories = val; } 
 publicvoidsetFat(intval){ fat = val; } 
 publicvoidsetSodium(intval) { sodium = val; } 
 publicvoidsetCarbohydrate(intval) { carbohydrate = val; } 
  
  
 publicstaticvoidmain(String[] args) { 
 NutritionFacts cocaCola =newNutritionFacts(); 
 cocaCola.setServingSize(240); 
 cocaCola.setServings(8); 
 cocaCola.setCalories(100); 
 cocaCola.setSodium(35); 
 cocaCola.setCarbohydrate(27); 
 } 
 } 

本节建议使用的是Builder模式：

 
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 // Builder Pattern - Pages 14-15 
  
 publicclassNutritionFacts { 
 privatefinalintservingSize; 
 privatefinalintservings; 
 privatefinalintcalories; 
 privatefinalintfat; 
 privatefinalintsodium; 
 privatefinalintcarbohydrate; 
  
 publicstaticclassBuilder { 
 // Required parameters 
 privatefinalintservingSize; 
 privatefinalintservings; 
  
 // Optional parameters - initialized to default values 
 privateintcalories=0; 
 privateintfat =0; 
 privateintcarbohydrate=0; 
 privateintsodium=0; 
  
 publicBuilder(intservingSize,intservings) { 
 this.servingSize = servingSize; 
 this.servings= servings; 
 } 
  
 publicBuilder calories(intval) 
 { calories = val;returnthis; } 
 publicBuilder fat(intval) 
 { fat = val;returnthis; } 
 publicBuilder carbohydrate(intval) 
 { carbohydrate = val;returnthis; } 
 publicBuilder sodium(intval) 
 { sodium = val;returnthis; } 
  
 publicNutritionFacts build() { 
 returnnewNutritionFacts(this); 
 } 
 } 
  
 privateNutritionFacts(Builder builder) { 
 servingSize= builder.servingSize; 
 servings = builder.servings; 
 calories = builder.calories; 
 fat= builder.fat; 
 sodium = builder.sodium; 
 carbohydrate = builder.carbohydrate; 
 } 
  
 publicstaticvoidmain(String[] args) { 
 NutritionFacts cocaCola =newNutritionFacts.Builder(240,8). 
 calories(100).sodium(35).carbohydrate(27).build(); 
 } 
 } 