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

 1 public class NutritionFacts {
 2 
 3     private final int servingSize;
 4     private final int servings;
 5     private final int calories;
 6     private final int fat;
 7     private final int sodium;
 8     private final int carbohydrate;
 9 
10     // 构造器，静态内部类
11     public static class Builder {
12         // 必要参数
13         private final int servingSize;
14         private final int servings;
15         // 可选参数
16         private int calories = 0;
17         private int fat = 0;
18         private int carbohydrate = 0;
19         private int sodium = 0;
20 
21         public Builder(int servingSize, int servings) {
22             this.servingSize = servingSize;
23             this.servings = servings;
24         }
25 
26         public Builder calories(int val) {
27             calories = val;
28             return this;//返回Builder类对象本身，以便把调用链接起来
29         }
30 
31         public Builder fat(int val) {
32             fat = val;
33             return this;
34         }
35 
36         public Builder carbohydrate(int val) {
37             carbohydrate = val;
38             return this;
39         }
40 
41         public Builder sodium(int val) {
42             sodium = val;
43             return this;
44         }
45 
46         public NutritionFacts build() {
47             return new NutritionFacts(this);
48         }
49     }
50 
51     private NutritionFacts(Builder builder) {
52         servingSize = builder.servingSize;
53         servings = builder.servings;
54         calories = builder.calories;
55         fat = builder.fat;
56         sodium = builder.sodium;
57         carbohydrate = builder.carbohydrate;
58     }
59 
60     @Override
61     public String toString() {
62         return "[" +
63                 "servingSize:" + servingSize +
64                 ",servings:" + servings +
65                 ",calories:" + calories +
66                 ",fat:" + fat +
67                 ",sodium:" + sodium +
68                 ",carbohydrate:" + carbohydrate +
69                 "]";
70     }
71 
72     public static void main(String[] args) {
73         NutritionFacts cocaCola = new NutritionFacts.Builder(240, 8)
74                 .calories(100).sodium(35).carbohydrate(27).build();
75 
76         System.out.println(cocaCola);
77     }
78 }

构造Map

 1 package com.jt.mongo.demo.basic.util;
 2 
 3 import java.util.HashMap;
 4 import java.util.Map;
 5 
 6 /**
 7  * 构建拥有多个值的Map(简化map操作):<br/>
 8  * map = ParamBuilder.of().withParam().withParam().withParam().build();.
 9  * 
10  * @author weihainan.
11  * @since 0.1 created on 2017/2/8.
12  */
13 public final class ParamBuilder {
14 
15     private Map<String, Object> paramMap = new HashMap<>(6);
16 
17     private ParamBuilder() {
18         // empty
19     }
20 
21     /**
22      * 获取ParamBuilder对象.
23      */
24     public static ParamBuilder of(){
25         return new ParamBuilder();
26     }
27 
28     /**
29      * 获取ParamBuilder对象并设置一对key-value.
30      */
31     public static ParamBuilder of(String paramName, Object paramValue) {
32         return new ParamBuilder().withParam(paramName, paramValue);
33     }
34 
35     /**
36      * 设置参数，可多次操作.
37      */
38     public ParamBuilder withParam(String paramName, Object paramValue) {
39         paramMap.put(paramName, paramValue);
40         return this;
41     }
42 
43     /**
44      * 获取最终的map.
45      */
46     public Map<String, Object> build() {
47         return paramMap;
48     }
49 }