易学设计模式五 建造模式（Builder）

遇到多个构造器参数(Constructor Parameters)时要考虑用构建器(Builder)

//营养素
public class NutritionFacts {
	
	private final int servingSize;
	private final int servings;
	private final int calories; //卡路里
	private final int fat;		//脂肪
	private final int sodium;	//钠
	private final int carbohydrate; //碳水化合物
	
	// 构造器，静态内部类
	public static class Builder {
		
		 // 必要参数
        private final int servingSize;
        private final int servings;
        // 可选参数
        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 calories) {
        	this.calories = calories;
        	return this;
        }
        
        public Builder sodium(int sodium) {
        	this.sodium = sodium;
        	return this;
        }
        
        public Builder fat(int fat) {
        	this.fat = fat;
        	return this;
        }
        
        public Builder carbohydrate(int carbohydrate) {
        	this.carbohydrate = carbohydrate;
        	return this;
        }
        //最后返回构建成功的对象
        public NutritionFacts build() {
        	return new NutritionFacts(this);
        }
	}
	//私有构造子
	private NutritionFacts(Builder builder) {
		this.servingSize = builder.servingSize;
		this.servings = builder.servings;
		this.calories = builder.calories;
		this.fat = builder.fat;
		this.sodium = builder.sodium;
		this.carbohydrate = builder.carbohydrate;
	}
	
	@Override
    public String toString() {
        // TODO Auto-generated method stub
        return "["+
                "servingSize:"+servingSize+
                ",servings:"+servings+
                ",calories:"+calories+
                ",fat:"+fat+
                ",sodium:"+sodium+
                ",carbohydrate:"+carbohydrate+
                "]";
    }
	
	public static void main(String [] args) {
		NutritionFacts cocaCola = new NutritionFacts.Builder(240, 8)
			.calories(100).sodium(35).carbohydrate(27).build();
		
		System.out.println(cocaCola.toString());
	}
}

输出结果：

[servingSize:240,servings:8,calories:100,fat:0,sodium:35,carbohydrate:27]

参考：http://www.cnblogs.com/xwdreamer/archive/2012/06/06/2538496.html