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设计模式之Builder模式

2024-09-23 23:32:03   214人阅读

　　在平时的项目开发中，我们会通过构造方法传参来实例化对象。

　　但在需要多个参数时，如果继续使用构造方法实例，编写代码会非常麻烦，而且在其他项目成员传参时特别容易出现传参错误的情况，这时我们不妨来使用Builder模式进行编写。

　　在使用Builder模式之前，我们先看下重叠构造器模式和JavaBeans模式：

1、 重叠构造器模式

技术分享
 1 package com.effectiveJava; 2  3 public class MultiContrucProduct { 4     private String name; 5     private float price; 6     private float weight; 7     private String introduction; 8     private String category; 9     10     public MultiContrucProduct(String name,float price){11         this(name,price,(float)0);12     }13     14     public MultiContrucProduct(String name,float price, float weight){15         this(name, price,weight,null);16     }17     18     public MultiContrucProduct(String name,float price,float weight,String introduction){19         this(name,price,weight,introduction,null);20     }21     22     public MultiContrucProduct(String name,float price,float weight,String introduction,String category){23         this.name = name;24         this.price = price;25         this.weight = weight;26         this.introduction = introduction;27         this.category = category;28     }29 30     public String getName() {31         return name;32     }33 34     public void setName(String name) {35         this.name = name;36     }37 38     public float getPrice() {39         return price;40     }41 42     public void setPrice(float price) {43         this.price = price;44     }45 46     public float getWeight() {47         return weight;48     }49 50     public void setWeight(float weight) {51         this.weight = weight;52     }53 54     public String getIntroduction() {55         return introduction;56     }57 58     public void setIntroduction(String introduction) {59         this.introduction = introduction;60     }61 62     public String getCategory() {63         return category;64     }65 66     public void setCategory(String category) {67         this.category = category;68     }69     70     71 }
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实例化对象：

 1 MultiContrucProduct multiContrucProduct = 2 new MultiContrucProduct("multiProduct", 10, 10, null, "cloth"); 

使用重叠构造器模式在参数较多时，比较繁杂，冗余代码多，而且在传参时容易出现参数类型，参数顺序不对，造成错误。

2、JavaBeans模式

技术分享
 1 package com.effectiveJava; 2  3 public class JavaBeanProduct { 4     private String name; 5     private float price; 6     private float weight; 7     private String introduction; 8     private String category; 9     10     public JavaBeanProduct(){11         12     }13 14     public String getName() {15         return name;16     }17 18     public void setName(String name) {19         this.name = name;20     }21 22     public float getPrice() {23         return price;24     }25 26     public void setPrice(float price) {27         this.price = price;28     }29 30     public float getWeight() {31         return weight;32     }33 34     public void setWeight(float weight) {35         this.weight = weight;36     }37 38     public String getIntroduction() {39         return introduction;40     }41 42     public void setIntroduction(String introduction) {43         this.introduction = introduction;44     }45 46     public String getCategory() {47         return category;48     }49 50     public void setCategory(String category) {51         this.category = category;52     }53     54     55 }
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实例化对象：

1 JavaBeanProduct javaBeanProduct = new JavaBeanProduct();2         javaBeanProduct.setName("javaBeanProduct");3         javaBeanProduct.setPrice(10);4         javaBeanProduct.setWeight(10);5         javaBeanProduct.setIntroduction(null);6         javaBeanProduct.setCategory("cloth");

 

使用JavaBeans模式编写较为简单，通过set方式也比较容易区分参数。但在构造过程中JavaBean可能处于不一致的状态，这时使用该实例将会导致失败。此外JavaBeans模式阻止了把类构造为不可变对象的

可能性，影响多线程中安全性处理。

3、Builder模式

技术分享
 1 package com.effectiveJava; 2  3 public class BuilderProduct { 4     private String name; 5     private float price; 6     private float weight; 7     private String introduction; 8     private String category; 9     10     private BuilderProduct(Builder builder){11         this.name = builder.name;12         this.price = builder.price;13         this.weight = builder.weight;14         this.introduction = builder.introduction;15         this.category = builder.category;16     }17     18     public static class Builder{19         private final String name;20         private final float price;21         private float weight;22         private String introduction;23         private String category;24 25         public float getWeight() {26             return weight;27         }28 29 30 31         public Builder setWeight(float weight) {32             this.weight = weight;33             return this;34         }35 36 37 38         public String getIntroduction() {39             return introduction;40         }41 42 43 44         public Builder setIntroduction(String introduction) {45             this.introduction = introduction;46             return this;47         }48 49 50 51         public String getCategory() {52             return category;53         }54 55 56 57         public Builder setCategory(String category) {58             this.category = category;59             return this;60         }61 62 63 64         public BuilderProduct builder(){65             return new BuilderProduct(this);66         }67         68         public Builder(String name,float price){69             this.name = name;70             this.price = price;71         }72     }73 }
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实例化对象：

1         BuilderProduct builderProduct =  new BuilderProduct.Builder("builderProduct",0)2                 .setCategory("cloth")3                 .setIntroduction(null)4                 .setWeight(10)5                 .builder();

 

Builder模式是综合了以上两种模式的优点，即保证了重叠构造器模式的安全性，也能兼顾JavaBeans模式的可读性。当然Builder模式还有其他的使用方式，本文只是展示了其中的一种使用。

 
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设计模式之Builder模式


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