该字段在JAVA中不可见

Question

我目前正在开发一个程序，在我的子类中，我需要一个无参数构造函数，用空字符串初始化对象。

我尝试过使用super，我有setter和getter方法，但我一直得到“field Person.name不可见”。我得到这个地址和电话号码以及。

如何使其可见，并且我可以在不提供构造函数参数的情况下初始化对象？如果我做错了什么并需要修复某些内容，请告诉我（：

    // Create a class named Person
public class Person {
    
    // Fields: name, address, and phone number. (2 points)
    private String name;
    private String address;
    private String phoneNumber;

    // No argument constructor that initializes the object with empty strings for name, address, and phone. (2 points)
    public Person () {


        super();
        this.name = "";
        this.address = "";
        this.phoneNumber = "";

    }

    // 3 argument constructor that initializes the object with a name, address, and a phone number. (2 points)
    public Person2 (String name, String address, String phoneNumber) {

        this.name = name;
        this.address = address;
        this.phoneNumber = phoneNumber;


    }

    // Getter/setter methods for each of the fields. (3 points)

    // set/get name
    public void setName (String name) {

        this.name = name;

    }

    public String getName () {

        return this.name;
    }

    // set/get address
    public void setAddress (String address) {

        this.address = address;
    }

    public String getAddress () {

        return this.address;
    }

    // set/get phone number
    public void setPhoneNumber (String phoneNumber) {


        this.phoneNumber = phoneNumber;

    }

    public String getPhoneNumber () {

        return this.phoneNumber;
    }


    // toString method that returns a string for the name, address, and phone number (2 points)
    // (you can override the toString method as part of a class which is pretty swag)
    public String toString() {

        return "Name: " + name + "\n" + "Address: " + address + "\n" + "Phone: " + phoneNumber;

    }

}

// Create a subclass of Person named Customer
class Customer extends Person {

    // A field for a customer number. (1 point)
    private String customerNumber;

    public Customer () {
        
        //  A no argument constructor that initializes the object with an empty string for the name, address, phone, and customer number. (2 points)
        super(name, address, phoneNumber);

    }

    // A 4 argument constructor that initializes the object with a name, address, a phone number, and a customer number. (2 points)
    public Customer2 (String name, String address, String phoneNumber, String customerNumber) {
        
        this.name = name;
        this.address = address;
        this.phoneNumber = phoneNumber;
        this.customerNumber = customerNumber;

    }

    // Getter/setter method for the customer number field. (1 point)
    public void setCustomerNumber (String customerNumber) {

        this.customerNumber = customerNumber;

    }

    // toString method that prints the information from the Person toString as well as the customer number (2 points) 
    public String toString() {

        return "Name: " + name + "\n" + "Address: " + address + "\n" + "Phone: " + phoneNumber + "\n" + "Customer Number: " + customerNumber;

    }


}

Answer 1

我不认为有任何实际需要在people类中调用超级构造函数。然而，在客户类的构造函数中，您应该只调用没有参数的超级构造函数。

编辑：或者你可以在声明时直接启动这些值，就像我上面的那个人说的。

另外，有点不相关，但是，你可以有一个构造函数，但是给参数默认值。所以你可以调用它，有参数和没有参数，而不需要重写它。

Answer 2

>

您不能访问或分配到任何其他类中的private字段，但声明该字段的类除外。

不能用类名称以外的任何名称声明构造函数。因此，Person2和Customer2都不是有效的构造函数或方法。（方法需要返回类型！）

构造函数必须显式（通过super调用）或隐式地在其超类中链接无参数构造函数。

基本上，您在超类中初始化私有字段的选择是使用super（...）调用来链接传递值的超类构造函数或调用子类构造函数中的超类setter方法。

例如，Customer中的4参数构造函数可以是：

public Customer (String name, String address, 
                 String phoneNumber, String customerNumber) {
    super(name, address, phoneNumber);
    this.customerNumber = customerNumber;
}

或者

public Customer (String name, String address, 
                 String phoneNumber, String customerNumber) {
    super();
    setName(name);
    setAddress(address);
    setPhoneNumber(phoneNumber);
    this.customerNumber = customerNumber;
}

在我看来，前者更好。它更简洁易读。

Customer中的toString（）方法不能直接引用人员的私有字段。它可以使用fields的getter。

Answer 3

如果字段被标记为私有访问，则只能从该类或其实例内部访问该字段。你应该使用get方法。或者，您可以获得toString的结果，并在此基础上进行构建。

此外，所有构造函数都应该与类同名（没有添加“2”）。

public class Person {
    
    private String name;
    private String address;
    private String phoneNumber;

    public Person() {
        this("", "", "");
    }

    public Person(String name, String address, String phoneNumber) {
        this.name = name;
        this.address = address;
        this.phoneNumber = phoneNumber;
    }

    public void setName (String name) {
        this.name = name;
    }

    public String getName () {
        return this.name;
    }

    public void setAddress (String address) {
        this.address = address;
    }

    public String getAddress () {
        return this.address;
    }

    public void setPhoneNumber (String phoneNumber) {
        this.phoneNumber = phoneNumber;
    }

    public String getPhoneNumber () {
        return this.phoneNumber;
    }

   @Override
    public String toString() {
        return "Name: " + name + "\n" + "Address: " + address + "\n" + "Phone: " + phoneNumber;
    }
}

// Create a subclass of Person named Customer
class Customer extends Person {

    private String customerNumber;

    public Customer () {
        this("", "", "", "");
    }

    public Customer (String name, String address, String phoneNumber, String customerNumber) {
        super(name, address, phoneNumber);
        this.customerNumber = customerNumber;
    }

    public String getCustomerNumber() {
        return customerNumber;
    }

    public void setCustomerNumber (String customerNumber) {
        this.customerNumber = customerNumber;
    }

    @Override
    public String toString() {
        return super.toString() + "\n" + "Customer Number: " + customerNumber;
    }
}