深入理解Java泛型类型擦除与Class字面量的获取

// 编译正常
Class<Student> studentClassType = Student.class;

// 编译错误：无法直接获取带有泛型类型参数的Class字面量
// Class<ArrayList<Student>> arrayListStudentClassType = ArrayList<Student>.class;

import java.util.ArrayList;
import java.util.List;

class Student {
    String name;
    public Student(String name) { this.name = name; }
}

public class GenericsClassLiteralDemo {
    public static void main(String[] args) {
        // 1. 获取非泛型类的Class对象：正常且包含完整类型信息
        Class<Student> studentClass = Student.class;
        System.out.println("Student class literal: " + studentClass);
        // 输出: Student class literal: class Student

        // 2. 尝试获取带有泛型类型参数的Class字面量：编译错误
        // Class<ArrayList<String>> arrayListStringClass = ArrayList<String>.class; // 编译错误！

        // 3. 获取泛型类的原始（raw）Class对象：正确
        Class<ArrayList> rawArrayListClass = ArrayList.class;
        System.out.println("Raw ArrayList class literal: " + rawArrayListClass);
        // 输出: Raw ArrayList class literal: class java.util.ArrayList

        // 4. 通过实例获取Class对象：
        // 得到的Class对象是原始类型，编译器为了类型安全会推断为Class<? extends ArrayList>
        List<String> stringList = new ArrayList<>();
        Class<? extends List> instanceListClass = stringList.getClass();
        System.out.println("Class from ArrayList<String> instance: " + instanceListClass);
        // 输出: Class from ArrayList<String> instance: class java.util.ArrayList

        // 验证通过实例获取的Class对象与原始Class对象是同一个
        System.out.println("Are raw ArrayList class and instance class the same? " + (rawArrayListClass == instanceListClass));
        // 输出: Are raw ArrayList class and instance class the same? true

        // 验证通过实例获取的Class对象与ArrayList<Integer>实例的Class对象也是同一个
        List<Integer> integerList = new ArrayList<>();
        Class<? extends List> instanceIntegerListClass = integerList.getClass();
        System.out.println("Class from ArrayList<Integer> instance: " + instanceIntegerListClass);
        System.out.println("Are raw ArrayList class and integer instance class the same? " + (rawArrayListClass == instanceIntegerListClass));
        // 输出: Are raw ArrayList class and integer instance class the same? true
    }
}