java - 如何从 Java 中的类型参数访问字段？

Question

我有两个类 X e Y 具有相同的静态成员:

class B {
    public static final String Base = "Base";
}

class X extends B {
    public static final String First = "First A";
    public static final String Second = "Second A";
}

class Y extends B {
    public static final String First = "First B";
    public static final String Second = "Second B";
}

在另一个类中，我需要一个将使用一个类或另一个类的函数:

class C {
    public <Data> void f() {
        System.out.println("Operation " + Data.Base);
        System.out.println("Running " + Data.First);
        System.out.println("Running " + Data.Second);
    }
}

想法是使用C如下:

C c = new C();
if (whatever()) {
    c.f<X>();
} else {
    c.f<Y>();
}

但上面的代码无效，有没有办法在 Java 中实现所需的行为？

Answer 1

你需要声明非静态方法

    abstract class B {
        public static final String Base = "Base";
        public abstract String getFirst();
        public abstract String getSecond();
    }

    class X extends B {
        public static final String First = "First A";
        public static final String Second = "Second A";

        public String getFirst() { return First; }
        public String getSecond() { return Second; }
    }

    class Y extends B {
        public static final String First = "First B";
        public static final String Second = "Second B";

        public String getFirst() { return First; }
        public String getSecond() { return Second; }
    }

    class C {
        public void f(B b) {
            System.out.println("Operation " + B.Base);
            System.out.println("Running " + b.getFirst());
            System.out.println("Running " + b.getSecond());
        }
}