构造器builder

遇到多个构造器参数时考虑用构造器

提到了流畅接口的问题

使用Builder来解决问题

Effective java的内容

当可变参数大于4个以上的时候用Builder，当然一开始就用是比较好的

public class Person {
//这里可以直接使用final没有问题的！！！
private final String firstName;//必填
private final String lastName;//必填

private String city;//下面3个是选填！
private String adress;
private boolean marry;

//这里考虑了用内部的Builder！也可以在外面声明Builder类

public static class Builder {//Builder是静态 类 ！！
private String firstName;//直接把里面的字段写下来
private String lastName;//这里需要不需要直接先    = null？？

private String city;//
private String adress;
private boolean marry;

public Builder (String firstName , String lastName){
this.firstName = firstName;
this.lastName = lastName;
}
public Builder setCity(String city){
this.city = city;
return this;
}
public Builder setAdress(String adress){
this.adress = adress;
return  this;
}
public Builder setMarry(boolean marry){
this.marry = marry;
return this;
}

public Person build(){
return new Person(this);
}
}
private Person(Builder builder){//构造方法私有化
firstName = builder.firstName;
lastName = builder.lastName;
city = builder.city;
adress = builder.adress;
marry = builder.marry;
}
}

下面的如何调用

public class test {
Person mPerson = new Person.Builder("xin","gao")
.setCity("henan")
.setMarry(false)
.build();//不是必填的可以随意添加
}

通过该Builder模式，以后如果在需要添加参数，直接在Builder中添加setXXX（）就行了！！

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