Question

我想将默认构造函数（person1）从public更改为private，然后让用户输入信息而不是给定值。

我有两个不同的类 - 人;这是封装的，然后是测试信息的PersonTest。

class Person {

// Data Members 
private String name; // The name of this person
private int age; // The age of this person
private char gender; // The gender of this person

// Default constructor
public Person() {
name = "Not Given";
age = 0;
gender = 'U';
}

// Constructs a new Person with passed name, age, and gender parameters.
public Person(String personName, int personAge, char personGender) {
name = personName;
age = personAge;
gender = personGender; 
}

// Returns the age of this person.
public int getAge( ) {
return age;
}

// Returns the gender of this person.
public char getGender( ) {
return gender;
}

// Returns the name of this person.
public String getName( ) {
return name;
}

// Sets the age of this person.
public void setAge( int personAge ) {
age = personAge;
}

// Sets the gender of this person.
public void setGender( char personGender ) {
gender = personGender;
}

// Sets the name of this person.
public void setName( String personName ) {
name = personName;
}

}

import java.util.Scanner;

public class PersonTest {

// Main method
public static void main(String[] args){

        // Create first instance of Person class to test the default constructor.
        Person person1 = new Person();

        // Create a new instance of the Person class.
        Person person2 = new Person();

        Scanner input = new Scanner(System.in);

        // Get the values from user for first instance of Person class.
        System.out.println("Person 2 Name: ");
        person2.setName(input.nextLine());

        System.out.println("Person 2 Age: ");
        person2.setAge(input.nextInt());

        System.out.println("Person 2 Gender: ");
        person2.setGender(input.next().charAt(0));


        // Print out the information.
        System.out.println("Person 1 Name = " + person1.getName());
        System.out.println("Person 1 Age = " + person1.getAge());
        System.out.println("Person 1 Gender = " + person1.getGender());
        System.out.println("");
        System.out.println("Person 2 Name = " + person2.getName());
        System.out.println("Person 2 Age = " + person2.getAge());
        System.out.println("Person 2 Gender = " + person2.getGender());
        System.out.println("");

}
}

Answer 1

如果您不想使用默认构造函数，则不要指定一个。只要编写至少一个带参数的构造函数，Java就不会提供默认构造函数，除非你有一个。

示例：

public class AClass
{
    int value = 0;
}

public class BClass
{
    int value;

    public BClass()
    {
        value = 0;
    }

    public BClass(int value)
    {
        this.value = value;
    }
}

这个类有默认构造函数，你可以编写

AClass a = new AClass();
BClass b = new BClass();

获取此类的新实例。

public class CClass
{
    int value;

    public CClass(int value)
    {
         this.value = value;
    }
}

此类没有default-constructor，因为至少指定了一个其他构造函数，并且没有写入default-constructor。因此

CClass c = new CClass();

将导致语法错误。

Answer 2

可以从“外部”访问构造函数的主要目的之一，以便外部类可以实例化和使用您的类。你不应该将构造函数设为私有。它将无法访问，因此它的主要目的将被违反！

在Java中将公共数据更改为私有数据

2 个答案: