在Java中使用父类名存储时如何返回继承的对象

Question

我正在尝试创建一个助手。我的应用程序可以有许多库，一旦实例化，我想创建一个工厂以便能够跨类共享实例，即：public ArrayList<Helper> helper = new ArrayList<>(asList(    new Helper(SomeLib.class, new SomeLib()),    new Helper(SomeOtherLib.class, new SomeOtherLib())));我的图书馆课程目前是测试这项工作的标准。class Library {    public Library() { System.out.println("Instance is working"); }}我试图开始工作的示例库如下所示：public class ExampleLib extends Library {    public void test() { System.out.println("Test OK"); }}我当前的 Helper 类看起来像这样，但是，我无法将库强制转换回原来的继承类，我尝试了多种方法：import dreambot.libs.Library;public class Helper {    private Library lib;    private Class<? extends Library> name;        public Helper(Class<? extends Library> name, Library lib) {        this.name = name;        this.lib = lib;    }        public Class<? extends Library> getName() { return name; }    public <Library> Library getLib() {        // All the things I've tried to do        return (this.name) lib;        return name.cast(lib);        return lib.getClass().cast(lib);    }}反过来，我想要的是：public ArrayList<Helper> helper = new ArrayList<>(asList(    new Helper(ExampleLib.class, new ExampleLib()),));public void test() {    Arrays.stream(helper.toArray()).filter(c -> c.getName(ExampleLib.class)).getFirst().ifPresent(h -> {        h.getLib().test(); // Should output "Test OK"    });我在 IDE 中收到的错误Helper::getLib是：不是一个声明return (this.name) lib;需要不兼容的类型：库，找到：dreambot.libs.Library for return lib.getClass().cast(lib);和return name.cast(lib);任何帮助，将不胜感激。

Answer 1

尝试：

import dreambot.libs.Library;

public class Helper<T extends Library> {

    private T lib;

    private Class<T> name;

    public Helper(Class<T> name, Library lib) {

        this.name = name;

        this.lib = lib;

    }

    public Class<T> getName() { return name; }

    public T getLib() {

        return lib;

    }

}

甚至更简单：

import dreambot.libs.Library;

public class Helper<T extends Library> {

    private T lib;

    public Helper(Library lib) {

        this.lib = lib;

    }

    public Class<T> getName() { return lib.getClass(); }

    public T getLib() {

        return lib;

    }

}

并且在调用构造函数时不要忘记钻石运算符：

public ArrayList<Helper> helper = new ArrayList<>(asList(

    new Helper<>(SomeLib.class, new SomeLib()),

    new Helper<>(SomeOtherLib.class, new SomeOtherLib())

));

可以简化为：

public ArrayList<Helper> helper = new ArrayList<>(asList(

    new Helper<>(new SomeLib()),

    new Helper<>(new SomeOtherLib())

));