《Effective java》--创建和销毁对象 2.遇到多个构参数是要考虑用构建器
eg
普通方法
poublic NutritionFacts{
private final int servingSize;
private final int servings;
private final int calories;
private final int fat;
private final int sodium;
private final int carbohdrate;
public NutritionFacts(int servingSize,int serving){
this(servingSize,servings,0);
}
public NutritionFacts(int servingSize,int serving,int calories){
this(servingSize,serving,calories,0);
}
public NutritionFacts(int servingSize,int serving,int calories,int fat){
this(servingSize,serving,calories,fat,0);
}
public NutritionFacts(int servingSize,int serving,int calories,int fat,int sodium){
this(servingSize,serving,calories,fat,sodium,0);
}
public NutritionFacts(int servingSize,int serving,int calories,int fat,int sodium,int carbohydrate){
this.servingSize = servingSize;
this.serving = serving;
this.calories= calories;
this.fat= fat;
this.sodium = sodium;
this.carbohydrate= carbohydrate;
}
}
此方法缺点，调用需要许多你不想设置的参数，但又不得不传。如果参数过多会导致错误。
javaBeans模式
public class NutritionFacts{private int servingSize;
private int servings;
private int calories;
private int fat;
private int sodium;
private int carbohdrate;
public NutritionFacts(){}
public void setServingSize(int val){servingSize = val;}
public void setServings(int val){servings= val;}
public void setCalories(int val){calories= val;}
public void setFat(int val){fat = val;}
public void setSodium(int val){sodium = val;}
public void setCarbohdrate(int val){carbohdrate = val;}
}
NutritionFacts cocaCola = new NutritionFacts ();
cocaCola .setServingSize(10);
cocaCola .setServings(20);
cocaCola .setCalories(10);
cocaCola .setFat(10);
cocaCola .setSodium(10);
cocaCola .setCarbohdrate(10);
此方法缺点：需要付出额外的努力来确保线程安全
Builder模式
public class NutritionFacts{
private final int servingSize;
private final int servings;
private final int calories;
private final int fat;
private final int sodium;
private final int carbohdrate;
public static class Builder{
//Required parameters
private final int servingSize;
private final int serving;
//Optional parameters - initialized to default values
private int calories = 0;
private int fat = 0;
private int sodium = 0;
private int carbohdrate = 0;
pubblic Builder(int servingSize,int servings){
this.servingSize = servingSize;
this.servings = servings;
}
public Builder calorise(int val){
calories = val;
return this;
}
public Builder fat(int val){
fat = val;
return this;
}
public Builder carbohdrate(int val){
carbohdrate = val;
return this;
}
public Builder sodium(int val){
sodium = val;
return this;
}
public Nutrition build(){
return new NutrionFacts(this);
}
}
private NutritionFacts(Builder builder){
servingSize = builder.servingSize;
servings = builder.servings;
calories = builder.calories;
fat = builder.fat;
sodium = builder.sodium;
carbohydrate = builder.carbohydrate;
}
}
Nutrition cocalCola = new Nutrition.Builder(240,80).calories(100).sodium(35).carbohydrate(27).builder();
劣势：为了创建对象，必须先创建他的构建器，虽然创建构建器开销的开销在实践中可能不那么明显，但是在某些十分重视性能的情况下，可能就成问题了，Build模式还比重叠构造更加冗长，因此只有在很多参数时才使用