如何动态访问对象属性？

const obj = { name: 'Alice', age: 30 };
const propertyName = 'age';

console.log(obj.name); // 输出：Alice
console.log(obj[propertyName]); // 输出：30

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

obj = Person('Alice', 30)
propertyName = 'age'

print(obj.name) # 输出：Alice
print(getattr(obj, propertyName)) # 输出：30

class Person {
    String name;
    int age;
}

Person obj = new Person();
obj.name = "Alice";
obj.age = 30;

String propertyName = "age";

System.out.println(obj.name); // 输出：Alice
System.out.println(obj.getClass().getField(propertyName).get(obj)); // 输出：30