java - 未声明的实例变量的初始化

Question

我是java新手，对此感到困惑: UserAccount 是另一个类 我如何在这个抽象类 Person 中初始化用户

public abstract class Person {
private String name;
private String email;
public Person(String name, String email, UserAccount user) {
//initalize user

    this.name = name;
    this.email = email;
//user?


}
public class UserAccount {
private String username;
private String password;
public UserAccount(String username, String password) {

    this.username = username;
    this.password = password;
}

Answer 1

在您的代码中，您执行了所谓的 Inversion of Control 操作，尽管它在这个场景中的应用可能不是最好的例子。当收到UserAccount时作为 Person 构造中的参数，您实际上可能想将其存储为类 Person 的字段/属性:

public abstract class Person {
    private String name;
    private String email;
    private User user; // Add field user

    public Person(String name, String email, UserAccount user) {
        this.name = name;
        this.email = email;
        this.user = user; // Inversion of Control: assume user is already constructed
    }
}

简而言之:您将构建 UserAccount在像这样构建用户之前:

// first construct the account...
UserAccount user = new UserAccount("John", "123secret321");
// ... then pass this account to a person
Person person = new Person("John", "john@doe.com", user);

但是，有可能让 Person 的构造函数全力做好UserAccount的 build 像这样:

    // signature has changed, pass all necessary information to Person, let it construct a UserAccount for us.
    public Person(String name, String email, String userName, String password) {
        this.name = name;
        this.email = email;
        this.user = new UserAccount(userName, password); // construct the user with the given information
    }

虽然你不能调用 Person 的构造函数直接地(因为类是 abstract )，当构造子类时，构造函数被调用，例如

public class FinishedPerson extends Person {
    private Date birthDate;

    public FinishedPerson(String name, String email, Date birthDate, String username, String password) {
        // call Person's constructor that, amongst other things, initializes the field user.
        super(name, email, username, password); 
        this.birthDate = birthDate;
    }
}

我希望这会有所帮助。