有没有一种方法可以访问对象中的对象？ [英] is there a way to access an object within an object?

问题描述

我正在通过构建一个简单的目录来练习Java。我有4节课。这些是：

I'm practicing java by building a simple directory. I have 4 Classes. These are:

1. 人员

1. Person

地址

联系

testClass

testClass

我已经完成了该系统的创建，并且可以按照我想要的方式工作。为此，我为人，地址和联系人创建了3个不同的数组。为了将人，地址和联系人链接在一起，我将它们放在具有相同索引号的相应数组上。 （并不是从字面上将它们链接在一起，只是一种在编辑人员时知道要访问哪个地址或联系人的方式。）

I have already finished creating this system and it works the way I want it. I did this by making 3 different arrays for the Person, Address and Contact. To link the Person, Address and Contact together I place them on there respective array with the same index number. (Not literally linking them together, just a way to know which address or contact to access when editing a person).

但是现在，我想对其进行优化。我想创建一个HashMap来容纳一个带有地址和联系人的人。有关更多信息，请参见下面的代码。

But now, I want to optimize it. I want to create a single HashMap to hold a person with the address and contacts within it. Please see my code below for more information.

Person.class

Person.class

public class Person {
private long Id;
private firtName;
private Address address;
private Contact contact;

//some setter and getter methods

public Person(Address address, Contact contact) {
this.address = address;
this.contact = contact;
}
}

Address.class

Address.class

public class Address {

private String street;
private String city;
private String province;


//some setter and getter methods
}

Contact.class

Contact.class

public class Contact {

private long Phone;
private String Email;

//some setter and getter methods
}

testClass .class

testClass.class

public class testClass {

public static void main(String[] args) {
HashMap<Integer, Person> person = new HashMap<Integer, Person>();

person.put(1, new Person(new Address(), new Contact)));
person.get(1).setStreet("place");

}

}

我的问题是，在testClass的这一行代码上

My question is, on this line of code in the testClass

person.get(1).setStreet("place");

是否可以直接访问/编辑此人的地址或联系人，而无需创建单独的数组或方法？

is there a way to directly access/edit the person's address or contact without creating a separate array or method?

推荐答案

private Address address;
private Contact contact;

如果要公开这些 的 private 您可以像这样直接访问它们：

If you were to make these public instead of private you would be able to access them directly like so:

Person person = new Person(new Address(), new Contact());

Person p = person.get(1);
String city = p.address.getCity();
String email = p.contact.getEmail();

但是这违反了封装原理（您应该隐藏内部字段，并且只能通过方法访问）

However this violates the principle of encapsulation (you should hide your inner fields and allow access only through methods).

相反，您应该按以下方式创建人类：

Instead you should create your person class as follows:

public class Person {
    private long Id;
    private firtName;
    private Address address;
    private Contact contact;

//some setter and getter methods

    public Person(Address address, Contact contact) {
        this.address = address;
        this.contact = contact;
    }

    public Address getAddress() {
        return address;
    }

    public Contact getContact() {
        return contact;
    }
}

并通过

Person p = person.get(1);
String city = p.getAddress().getCity();
String email = p.getContact().getEmail();

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