[英]What's wrong with my builder pattern?
我在实现Builder模式时遇到问题。 我有2节课:
package course_2;
import java.util.Date;
public class Student {
private static int idStart = 0;
private final int id = idStart++;
private String name;
private String surname;
private String secondName;
private Date birthDate;
private String address;
private String phone;
private int course;
private int group;
public static class Builder {
// Обязательные параметры
private final String name;
private final String surname;
private final Date birthDate;
// Необязательные параметры, инициализация по умолчанию
private String secondName = "";
private String address = "";
private String phone = "";
private int course = 1;
private int group = 1;
public Builder(String name, String surname, Date birthDate) {
this.name = name;
this.surname = surname;
this.birthDate = (Date) birthDate.clone();
}
public Builder SecondName(String secondName) {
this.secondName = secondName;
return this;
}
public Builder address(String address) {
this.address = address;
return this;
}
public Builder phone(String phone) {
this.phone = phone;
return this;
}
public Builder course(int course) {
this.course = course;
return this;
}
public Builder group(int group) {
this.group = group;
return this;
}
}
private Student(Builder builder) {
this.name = builder.name;
this.surname = builder.surname;
this.secondName = builder.secondName;
this.birthDate = builder.birthDate;
this.address = builder.address;
this.phone = builder.phone;
this.course = builder.course;
this.group = builder.group;
}
}
问题是当我尝试从客户端代码调用Builder时:
Student studentOne = new Student.Builder("Andrue", "Booble", /*Date variable here*/);
我遇到了编译器问题:
错误:(24,30)java:不兼容的类型:course_2.Student.Builder无法转换为Course_2.Student
有人可以帮助我理解吗,为什么会发生以及如何解决? 谢谢!
您需要将以下内容添加到Builder
:
public Student build(){
return new Student(this);
}
并这样称呼它:
Student studentOne = new Student.Builder("Andrue", "Booble", null).build();
new Student.Builder("Andrue", "Booble", /*Date variable here*/);
返回您的生成器对象而不是学生。
您的工厂缺少调用Student构造函数的方法create
它应该看起来像这样
public Student create(){
return new student (this);
}
并在Builder
类中实现
现在,如果您要创建学生,请致电
Student studentOne = new Student.Builder("Andrue", "Booble", /*Date variable here*/).create();
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