How do you get to mandatory classes?

In the case of Java, not always. The class does require a constructor, but the compiler will automatically include an "empty constructor" (constructor without parameters) under certain conditions.

In C, no. In Java, yes.

You always should define default constructor for your class. You must also define a copy constructor for your class if there are any pointers in the class.While it is not mandatory, failure to...

They try to prevent obesity.

No, not always, but if you don't, you will get a default constructor that might not properly initialize the instance correctly. It depends on what you are trying to do. The best answer is yes, you...