java在没有类型转换的情况下访问父类型的arraylist中的特定子类型方法，子类型的创建只有在运行时才知道

1 月，3 周 Questions & Answers 31

我有以下父类：

public class Employee {
    private String name;

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

    public String getName() {
        return name;
    }
}

和扩展父类的2个子类：

public class FullTimeEmployee extends Employee {
    private double salary;

    public FullTimeEmployee(String name, double salary) {
        super(name);
        this.salary = salary;
    }

    public double getSalary() {
        return salary*2;
    }
}

public class PartTimeEmployee extends Employee {
    private double salary;

    public PartTimeEmployee(String name, double salary) {
        super(name);
        this.salary = salary;
    }   

    public double getSalary() {
        return salary;
    }   
}

情景：我正在使用ArrayList来包含有关员工的信息。ArrayList是在程序开始时创建的，添加到ArrayList中的员工类型是扩展父级的子级，只有在运行时通过用户输入才知道

public class EmployeeApplication {

    public static void displayInfo(Employee employee) {
        
        // How do I access the method getSalary() that belong to the specific type determined on runtime?
        System.out.println(employee.getSalary()); //  <--- ???
    }
    
    
    public static void main(String[] args) {
        
        Scanner keyboardInput = new Scanner(System.in);
            
        System.out.println("Type of employee to add into arraylist: ");
        String userInput = keyboardInput.nextLine();
        
        // ArrayList to contain information about employees
        ArrayList<Employee> employeeAL = new ArrayList<Employee>();
        
        // Type of employee being created and added into ArrayList is dynamic and only known at run time based on user input
        if(userInput.equals("full")) {
            employeeAL.add(new FullTimeEmployee("John", 1000));
        }
        else {
            employeeAL.add(new PartTimeEmployee("John", 500));
        }
        
        displayInfo(employeeAL.get(0));
        
        keyboardInput.close();      
    }
}

现在的问题是：如何访问属于运行时确定的特定子类型的getSalary（）方法？因为从ArrayList检索的对象是父类型。请注意，工资属性只属于子类

我当前的实现让我检查子类型，将其类型转换为该子类型，最后访问属于该子类型的方法

我试图避免类型转换，因为我相信我在良好的Java编码实践方面做得不对。我错过了一些东西，但我不知道是什么

我考虑过的另一种方法是在父类中实现getSalary（）方法，并在子类中覆盖它，这样，我不必打字，但我不知道这是否是正确的做法，因为salary属性与Employee根本没有关系：

// Parent public class Employee { private String name; public Employee(String name) { this.name = name; } public String getName() { return name; } // ADDED THIS <---- public double getSalary() { return 0.0; } } // Child public class FullTimeEmployee extends Employee { private double salary; public FullTimeEmployee(String name, double salary) { super(name); this.salary = salary; } // ADDED THIS <---- @Override public double getSalary() { return salary*2; } }

我做错了什么？最好的Java编码实践是什么

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java在没有类型转换的情况下访问父类型的arraylist中的特定子类型方法，子类型的创建只有在运行时才知道

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