如何在动态继承中确保类型

public interface TypeCheck {
    void checkType();
}

public class Parent implements TypeCheck {
    @Override
    public void checkType() {
        System.out.println("Parent type checked.");
    }
}

public class Child extends Parent {
    @Override
    public void checkType() {
        System.out.println("Child type checked.");
    }
}

public class Main {
    public static void main(String[] args) {
        TypeCheck obj;

        // 动态选择父类
        obj = new Parent();
        obj.checkType(); // 输出：Parent type checked.

        obj = new Child();
        obj.checkType(); // 输出：Child type checked.
    }
}