Type Erasure类型擦除

Generics were introduced to the Java language to provide tighter type checks at compile time and to support generic programming. Java语言中引入了泛型，以在编译时提供更严格的类型检查，并支持泛型编程。To implement generics, the Java compiler applies type erasure to:为了实现泛型，Java编译器将类型擦除应用于：

• Replace all type parameters in generic types with their bounds or Object if the type parameters are unbounded. 如果类型参数是无界的，则用其边界或Object替换泛型类型中的所有类型参数。The produced bytecode, therefore, contains only ordinary classes, interfaces, and methods.因此，生成的字节码只包含普通类、接口和方法。
• Insert type casts if necessary to preserve type safety.如有必要，插入类型强制转换以保持类型安全。
• Generate bridge methods to preserve polymorphism in extended generic types.生成桥接方法以在扩展泛型类型中保留多态性。

Type erasure ensures that no new classes are created for parameterized types; consequently, generics incur no runtime overhead.类型擦除确保没有为参数化类型创建新类；因此，泛型不会产生运行时开销。