在 Java 中实例化一个泛型类 [英] Instantiating a generic class in Java

问题描述

我知道 Java 的泛型比 .Net 的要差一些.

I know Java's generics are somewhat inferior to .Net's.

我有一个通用类 Foo，我真的需要使用无参数构造函数在 Foo 中实例化一个 T.如何解决 Java 的局限性?

I have a generic class Foo<T>, and I really need to instantiate a T in Foo using a parameter-less constructor. How can one work around Java's limitation?

推荐答案

一个选项是传入 Bar.class(或您感兴趣的任何类型 - 指定适当的Class 引用)并将该值保留为字段:

One option is to pass in Bar.class (or whatever type you're interested in - any way of specifying the appropriate Class<T> reference) and keep that value as a field:

public class Test {
    public static void main(String[] args) throws IllegalAccessException,
            InstantiationException {
        Generic<Bar> x = new Generic<>(Bar.class);
        Bar y = x.buildOne();
    }
}

public class Generic<T> {
    private Class<T> clazz;

    public Generic(Class<T> clazz) {
        this.clazz = clazz;
    }

    public T buildOne() throws InstantiationException, IllegalAccessException {
        return clazz.newInstance();
    }
}

public class Bar {
    public Bar() {
        System.out.println("Constructing");
    }
}

另一种选择是拥有一个工厂"接口，并将工厂传递给泛型类的构造函数.这样更灵活，您无需担心反射异常.

Another option is to have a "factory" interface, and you pass a factory to the constructor of the generic class. That's more flexible, and you don't need to worry about the reflection exceptions.

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