this() and super(), both are the constructors that’s why must be the first statement. But we can use both in a program. this(): It is used to call, same class Default or Parametrized Constructor. super(): It is used to call, immediate super/parent class Default or Parametrized Constructor.
For More Information Please Refer: https://stackoverflow.com/questions/10381244/why-cant-this-and-super-both-be-used-together-in-a-constructor