java - 如何限制子类访问父类(super class)方法？

Question

例如:

我有课

package test.inheritance.checkMultiple;

public class Company {



protected void run (){
    System.out.println("Time to Run");
}

}

public class Department extends Company {



    public void testDepartment()
    {
        Department d =new Department();
        d.run();
    }

}


public class Employee extends Department{


    public void checkValidEmployee(){
        Employee e =new Employee();
        e.run();
        e.testDepartment();

    }

    public static void main (String[] artgs)
    {
        Employee e =new Employee();
        e.checkValidEmployee();
        System.out.println("Valid Emplyee");
    }

}

1) 我不希望员工类有权访问 run 方法。为此我该怎么办？

2)如果我想给员工类访问run方法，但不给部门类，我该怎么办？

Answer 1

你不应该这样做，因为每个子类都必须是它所属子类的有效类 - 请参阅 Liskovs substitution principle .

因此，按照 @Michael Laffargue 的建议，使用组合而不是继承。

我不知道你到底想要实现什么，但它应该看起来更像下面这样，其中 Company 是 Department 的成员变量，而 Department 又是 Employee 的成员变量。

import java.util.Arrays;
import java.util.List;

public class Company
{
    private final String name;

    public Company(String name)
    {
        this.name = name;
    }

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

    public void run()
    {
        System.out.println("Time to Run");
    }
}

public class Department
{
    private static final List<String> VALID_DEPARTMENTS = Arrays.asList("IT");
    private final String name;
    private final Company company;

    public Department(String name, Company company)
    {
        this.name = name;
        this.company = company;
    }

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

    public Company getCompany()
    {
        return this.company;
    }

    public void checkValid()
    {
        if (!VALID_DEPARTMENTS.contains(this.name))
            throw new AssertionError();
    }

}

public class Employee
{
    private final Department department;
    private final String name;

    public Employee(String name, Department department)
    {
        this.department = department;
        this.name = name;
    }

    public void checkValid()
    {
        this.department.getCompany().run();
        this.department.checkValid();
    }

    public Department getDepartment()
    {
        return this.department;
    }

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

public class Main
{
    public static void main(String[] artgs)
    {
        final Company company = new Company("Company");
        final Department department = new Department("IT", company);
        Employee e = new Employee("Peter", department);
        e.checkValid();
        System.out.println("Valid Emplyee");
    }
}