文章标题

通常我们在遇到构造器参数过多时我们会考虑使用重叠构造器与JavaBeans模式处理，但重叠构造器当参数过多时，会造成客户端代码难以编写。而JavaBeans虽然有利于客户端代码的开发，但是由于构造过程被分到了几个调用中，也就是JavaBeans模式阻止了把类做成不可变的可能，需要额外提供线程安全。例子代码如下：

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 carbohydrate;

public static class Builder{
private final int servingSize;
private final int servings;

private int calories = 0;
private int fat = 0;
private int carbohydrate = 0;
private int sodium = 0;

public Builder(int servingSize,int servings){
this.servingSize = servingSize;
this.servings = servings;
}

public Builder calories(int val){
calories = val;
return this;
}
public Builder fat(int val){
fat = val;
return this;
}
public Builder carbohydrate(int val){
carbohydrate = val;
return this;
}
public Builder sodium(int val){
sodium = val;
return this;
}

public NutritionFacts build(){
return new NutritionFacts(this);
}
}
private NutritionFacts(Builder builder){
servingSize = builder.servingSize;
sevings = builder.servings;
calories = builder.calories;
fat = builder.fat;
sodium = builder.sodium;
carbohydrate = builder.carbohydrate;
}
}

调用示例：

NutritionFacts cola = new NutritionFacts.Builder(240,8).calories(100).sodium(35).carbohydrate(27).build();