java builder模式

今天药忘吃喽~ 2022-03-01 03:10 169阅读 0赞

java builder模式主要是用一个内部类去实例化一个对象，避免一个类出现多个构造函数，并且构造函数如果出现默认参数，就比较容易出错。  
不直接生成想要的对象，而是让客户端利用所有必要的参数调用构造器，得到一个builder对象，然后客户端在builder对象上调用类似于setter的方法，来设置每个相关的可选参数，最后客户端调用无参数的build方法来生成不可变的对象。

public class test2 {
    	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{
    		//必备参数
    		private final int servingsize;
    		private final int servings;
    		//可选参数，初始化
    		private int calories=0;
    		private int fat=0;
    		private int sodium=0;
    		private int carbohydrate=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 sodium(int val) {
    			sodium=val;
    			return this;
    		}
    		public Builder carbohydrate(int val) {
    			carbohydrate=val;
    			return this;
    		}
    		public test2 build() {
    			return new test2(this);
    		}
    	}
    	private test2(Builder builder) {
    		servingsize=builder.servingsize;
    		servings=builder.servings;
    		calories=builder.calories;
    		fat =builder.fat;
    		sodium=builder.sodium;
    		carbohydrate=builder.carbohydrate;
    		
    	}
    
    }

客户端调用：

test2 cocacola=new test2.Builder(240, 8).calories(100).carbohydrate(27).build();

这样就可以随意设置自己想要自定义的参数。