how java determines which method to run: at the time a program gets compiled, methods in or inherited by the declared type determine the corectness of a non static method call.
Person person1 = new Student();
person1.getName();java will only check the person class. If the person class does not have a getName then it wont do it.
when the program actually runs then it will look at the object as a student object, and in doing so it will first check the Student class for a getName method, and if it does exist then java will use the getName method from the student class. If it doesn’t exist it will look in the parent class.
but if you try to make a printGrade() method in the student class, and then say
Person lovelace = new Student(“ada”,12);
then try to
lovelace.printGrade()
it will not compile, as the person class has no such method.
Several situations require this:
- You may want an array that stores different types of people and declaring lovelace as a Person allows you to combine the object with the other person objects
- For scope purposes sometimes you need to declare the variable before you know what type of object you will have
Recap:
- At compile time, method in or inherited by the declared type determine the correctness of a non-static method call.
- At run-time, the method in the actual object type is exceuted for a non static method call.