不加其實也沒有影響，子類的無參或者有參構造函數都會默認調用父類的無參構造函數，老師這里可能只是強調一下Exception中默認構造函數做的工作吧。

public?class?TestExtends?{
????
????public?static?void?main(String[]?args)?{
????????new?Child();
??????System.out.println("-----------");
??????new?Child(1,"1");
????}
????
}

class?Parent?{
????
????protected?Integer?id;
????protected?String?name;

????public?Parent()?{
????????System.out.println("parent?no?arg?constructor");
????}

????public?Parent(Integer?id,?String?name)?{
????????this.id?=?id;
????????this.name?=?name;
????????System.out.println("parent?all?args?constructor");
????}
}

class?Child?extends?Parent{

????public?Child()?{
????????System.out.println("child?no?arg?constructor");
????}

????public?Child(Integer?id,?String?name)?{
????????this.id?=?id;
????????this.name?=?name;
????????System.out.println("child?all?args?constructor");
????}

}

打印

parent no arg constructor

child no arg?constructor

-----------

parent no arg constructor

child all args constructor