英文:
Question about return type( need to return instances of different classes) in generics
问题
以下是翻译好的部分：
所以我的当前代码看起来是这样的。这个想法是使用通用类型 T 接收不同类的实例，然后返回这些实例。我应该能够像这样调用类的实例：```javanew A().add(new B())
public static <T> T add(T t) {return new T();}
基本上对我来说，返回类型应该是类本身，这样它可以通过返回类型获取一个新的实例。
有人能指导我逻辑出了什么问题吗？
<details><summary>英文:</summary>So my current code looks like this. The idea is to take in an instance of different classes using generic type T and return those instances.I should be able to call instances of classes like this
new A().add(new B())
public static <T> T <T> add(T t) {return new T();}
Basically to me the return type should be the class itself so that it can take a new instance through the return type.Can someone guide me as to where my logic is going wrong?</details># 答案1**得分**: 1你不能仅通过泛型类型调用构造函数，因为：1. 类型擦除意味着在运行时，`T` 会变成 `Object`（或者是其上界的类型），2. 你不知道构造函数是否一定不带参数。一个更好的方法是使用 [`Supplier`][1]：```javapublic static <T> T add(Supplier<T> supplier) {return supplier.get();}
你可以像这样使用这个方法。使用方法引用，可以非常简洁。
B b = YourClass.add(B::new);
英文:
You can't call a constructor just from the generic type because 1. type erasure means T gets turned into Object (or whatever its upper bound is) at runtime, and 2. you don't know that the constructor necessarily takes 0 arguments.
A better way to do it would be with a Supplier
public static <T> T add(Supplier<T> supplier) {return supplier.get();}
and you could use this method like this. With method references, it's pretty concise.
B b = YourClass.add(B::new);
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