java - 我想添加通用类型编号

Question

我有一个名为 Employee 的简单类。

public class Employee<T extends Number> {
    private final String id; 
    private final String name;
    private final T salary; //generic type salary

    public Employee(String id,String name,T salary){
        this.id = id;
        this.name = name;
        this.salary = salary;
    }

    public String getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public T getSalary() {
        return salary;
    }

}

这里使用缩减，我可以添加 Double 类型。但我需要通用类型添加。 salary 中的值可以是 Double 或 Integer。那么有没有什么方法可以提供任何灵 active ，以便我可以添加任何子类型的数字。

  public static void main(String[] args) {
        //creates employee list and three employees in it
        List < Employee > employees = new LinkedList < > ();
        employees.add(new Employee("E001", "John", 30000.00));
        employees.add(new Employee("E002", "Mark", 45000.00));
        employees.add(new Employee("E003", "Tony", 55000.00));
        employees.stream().map(Employee::getSalary).reduce(0, (a, b) -> {
        //only able to add double type values, but i need any sub type of number
                return a.doubleValue() + b.doubleValue();
            });
    }



Please help me. 

Answer 1

我建议您首先在变量声明中添加正确的泛型类型参数:

List<Employee<Double>> employees = new LinkedList<>(); // you need to add "<>"s here
employees.add(new Employee<>("E001", "John", 30000.00));
employees.add(new Employee<>("E002", "Mark", 45000.00));
employees.add(new Employee<>("E003", "Tony", 55000.00));

然后，这将返回一个可转换为Number的double，并且Number可以转换为int、float、short 等:

Number num = employees.stream().map(Employee::getSalary).reduce(0.0, (a, b) -> {
        return a + b;
});

或者，摆脱泛型。不使用 T，而是使用 Number 作为工资类型。

class Employee {
    private final String id;
    private final String name;
    private final Number salary; //generic type salary

    public Employee(String id,String name,Number salary){
        this.id = id;
        this.name = name;
        this.salary = salary;
    }

    public String getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public Number getSalary() {
        return salary;
    }

}