建造者模式之项目运用

1 问题

建造者模式，我们也许不陌生，因为我们看到很多开源框架或者Android源码里面用到，类似这样的代码结构

A a = new A.builder().method1("111").method2("222").build();
 

很明显，一般这里的结构有builder()构造函数，还有build()函数，主要用来干嘛呢？还不是为了构建对象，如果需要设置的参数很多的话，一个一个去set很繁琐也不好看，下面有个例子简单粗暴展示。 

2 测试代码实现

  

   

    

     

    
    

     

      package com.example.test1;
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      public class Student {
     
    
   

    

     

    
    

     
 private int id;
     
    
   

    

     

    
    

     
 private String name;
     
    
   

    

     

    
    

     
 private int age;
     
    
   

    

     

    
    

     
 private String classNmae;
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 public Student(Builder builder) {
     
    
   

    

     

    
    

     
 this.id = builder.id;
     
    
   

    

     

    
    

     
 this.name = builder.name;
     
    
   

    

     

    
    

     
 this.age = builder.age;
     
    
   

    

     

    
    

     
 this.classNmae = builder.classNmae;
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     
 public int getId() {
     
    
   

    

     

    
    

     
 return id;
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 public String getName() {
     
    
   

    

     

    
    

     
 return name;
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 public int getAge() {
     
    
   

    

     

    
    

     
 return age;
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 public String getClassNmae() {
     
    
   

    

     

    
    

     
 return classNmae;
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 @Override
     
    
   

    

     

    
    

     
 public String toString() {
     
    
   

    

     

    
    

     
 return "Student{" +
     
    
   

    

     

    
    

     
 "id=" + id +
     
    
   

    

     

    
    

     
 ", name='" + name + '\'' +
     
    
   

    

     

    
    

     
 ", age=" + age +
     
    
   

    

     

    
    

     
 ", classNmae='" + classNmae + '\'' +
     
    
   

    

     

    
    

     
 '}';
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 public static class Builder {
     
    
   

    

     

    
    

     
 private int id;
     
    
   

    

     

    
    

     
 private String name;
     
    
   

    

     

    
    

     
 private int age;
     
    
   

    

     

    
    

     
 private String classNmae;
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 public Builder() {}
     
    
   

    

     

    
    

     
 public Builder id(int id) {
     
    
   

    

     

    
    

     
 this.id = id;
     
    
   

    

     

    
    

     
 return this;
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     
 public Builder name(String name) {
     
    
   

    

     

    
    

     
 this.name = name;
     
    
   

    

     

    
    

     
 return this;
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     
 public Builder age(int age) {
     
    
   

    

     

    
    

     
 this.age = age;
     
    
   

    

     

    
    

     
 return this;
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     
 public Builder className(String classNmae) {
     
    
   

    

     

    
    

     
 this.classNmae = classNmae;
     
    
   

    

     

    
    

     
 return this;
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     
 public Student build() {
     
    
   

    

     

    
    

     
 return new Student(this);
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     

      }
     
    
  
 

  

   

    

     

    
    

     

       Student student = new Student.Builder()
     
    
   

    

     

    
    

     

       .name("chenyu")
     
    
   

    

     

    
    

     

       .age(28)
     
    
   

    

     

    
    

     

       .id(1)
     
    
   

    

     

    
    

     

       .className("erzhong")
     
    
   

    

     

    
    

     

       .build();
     
    
   

    

     

    
    

     
 Log.i(TAG, "student toString is:" + student.toString());
     
    
  
 

3 运行结果

18376-18376/com.example.test1 I/chenyu: student toString is:Student{id=1, name='chenyu', age=28, classNmae='erzhong'}
 

4 总结

1）我们需要构建一个对象很多参数的时候用这种方式

2）最关键的是需要构建的对象类里面有个Builder类作为参数传递

  

   

    

     

    
    

     
 public Student(Builder builder) {
     
    
   

    

     

    
    

     
 this.id = builder.id;
     
    
   

    

     

    
    

     
 this.name = builder.name;
     
    
   

    

     

    
    

     
 this.age = builder.age;
     
    
   

    

     

    
    

     
 this.classNmae = builder.classNmae;
     
    
   

    

     

    
    

     

       }
     
    
  
 

3）最后build()函数里面返回的是需要构建的类本身

  

   

    

     

    
    

     
 public Student build() {
     
    
   

    

     

    
    

     
 return new Student(this);
     
    
   

    

     

    
    

     

       }
     
    
  
 

文章来源: chenyu.blog.csdn.net，作者：chen.yu，版权归原作者所有，如需转载，请联系作者。

原文链接：chenyu.blog.csdn.net/article/details/105058815