设计模式 构造者模式

简述

Builder模式可以将一个类的构建和表示进行分离。

例子

http://www.cnblogs.com/cc11001100/p/5939220.html

* 使用 builder 模式

    public class Student {

    private int id;
    private String name;
    private String passwd;
    private String sex;
    private String address;

    // 构造器尽量缩小范围
    private Student() {
    }

    // 构造器尽量缩小范围
    private Student(Student origin) {
        // 拷贝一份
         this.id = origin.id;
        this.name = origin.name;
        this.passwd = origin.passwd;
        this.sex = origin.sex;
        this.address = origin.address;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public String getPasswd() {
        return passwd;
    }

    public String getSex() {
        return sex;
    }

    public String getAddress() {
        return address;
    }

    /**
     * Student的创建完全依靠Student.Builder，使用一种方法链的方式来创建
     *
     */
    public static class Builder {

        private Student target;

        public Builder() {
            target = new Student();
        }

        public Builder address(int id) {
            target.id = id;
            return this;
        }

        public Builder name(String name) {
            target.name = name;
            return this;
        }

        public Builder password(String passwd) {
            target.passwd = passwd;
            return this;
        }

        public Builder sex(String sex) {
            target.sex = sex;
            return this;
        }

        public Builder address(String address) {
            target.address = address;
            return this;
        }

        public Student build() {
            return new Student(target);
        }
    
    }

}

• 不使用 builder 模式

    public class Student {
  
    private int id;
    private String name;
    private String passwd;
    private String sex;
    private String address;
  
    public Student() {
    }
  
    public Student(String name, String passwd, String sex, String address) {
        super();
          this.name = name;
          this.passwd = passwd;
          this.sex = sex;
          this.address = address;
    }
  
    public int getId() {
        return id;
    }
  
    public void setId(int id) {
        this.id = id;
    }
  
    public String getName() {
        return name;
    }
  
    public void setName(String name) {
        this.name = name;
    }
  
    public String getPasswd() {
        return passwd;
    }
  
    public void setPasswd(String passwd) {
        this.passwd = passwd;
    }
  
    public String getSex() {
        return sex;
    }
  
    public void setSex(String sex) {
        this.sex = sex;
    }
  
    public String getAddress() {
        return address;
    }
  
    public void setAddress(String address) {
        this.address = address;
    }
  }
  

那么，使用 builder 模式在创建对象的时候，使用

Student s = newStudent.Builder().name("CC").password("qwerty").sex("男").address("xxx").build();

的方式可以创建，通过 builder 这个内部类的方法来规定参数的值，并且最后返回一个这样的对象，优点是参数内容清晰。而一般的创建对象时嗲用 set 方法的方式参数意义很难表达。
（后面可以多个方法列举的原因是每个方法都返回了一个 builder 对象）