在初始化时实现实例的抽象方法

Question

有一种方法可以在Java中实现C#初始化实例的抽象方法吗？

public static abstract class A
{
    public abstract String GetMsg();

    public void Print()
    {
        System.out.println(GetMsg());
    }
}

public static void main(String[] args)
{
    A a = new A()
    {
        @Override
        public String GetMsg()
        {
            return "Hello";
        }
    };

    a.Print();
}

Answer 1

不,你不能 - 但你可以通过使用Func<string>:

using System;

namespace Demo
{
    public sealed class A
    {
        public Func<string> GetMsg { get; }

        public A(Func<string> getMsg)
        {
            GetMsg = getMsg;
        }

        public void Print()
        {
            Console.WriteLine(GetMsg());
        }
    }

    public static class Program
    {
        public static void Main()
        {
            var a = new A(() => "Hello");
            a.Print();
        }
    }
}

或者,如果您希望能够GetMsg在初始化后更改属性:

using System;

namespace Demo
{
    public sealed class A
    {
        public Func<string> GetMsg { get; set; } = () => "Default";

        public void Print()
        {
            Console.WriteLine(GetMsg());
        }
    }

    public static class Program
    {
        public static void Main()
        {
            var a = new A(){ GetMsg = () => "Hello" };
            a.Print();
        }
    }
}

(这使用了c#6语法 - 你必须为早期版本略微修改它.)