Why my overriding method of toString() has to be public?

Question

I am new to Java and I am learning the basics. I was studying the toString method and how to override it in my own classes. I am just wondering why has toString to be public? is it because it is defined so in the Object class?

Answer 1

From official Oracle documentation:

Modifiers

The access specifier for an overriding method can allow more, but not less, access than the overridden method. For example, a protected instance method in the superclass can be made public, but not private, in the subclass.

This because inheritance creates an IS-A relation between two classes, for which the Liskov substitution principle must be valid. Without having the previous constraint that would be impossible to enforce.

Answer 2

Think about it: You subclass Gizmo with MyGizmo. This means that any place that a Gizmo can be used, you can use a MyGizmo in it's place. If some program does gizmoObject.toString() then that should work even if gizmoObject is not a Gizmo but a MyGizmo.

In particular, toString is used for printing & dumping objects and needs to be accessible on all objects.

Answer 3

When you override any method, the visibility of the override must be at least as visible as the base method.

Answer 4

When you override any method, the visibility of the override must be equal or more than the visibility of the base method

Answer 5

When overriding a method, you should declare the visibility of overridden method as the the one in the base class or wider.

Here is a note about the overriding rules I wrote it myself as a reference to me:

/* Access Modifiers */

1- Access modifier in child should be same or greater (the sequence: public - protected - default (package-private) - private). Access modifier in parent should not be private. If a child don't have access to the parent's method, then overriding the method without the @Override annotation will consider it as a new method.

/* Return Types */

2- Return type in child should be the same class or sub-class.

/* Exceptions */

3- If the parent's method throws checked exception, then the child's method can: a- throw the same exception or sub-class. b- not to throw any exceptions. c- throw runtime exceptions.

4- If the parent's method throws unchecked exception, then the child's method can: a- not to throw any exceptions. b- throw runtime exceptions.

5- If the parnet's method does not throw exception, then the child's method can: a- not to throw any exceptions. b- throw runtime exceptions.

Answer 6

Because you are overriding a method, you must define it as the prototype method or more than that.

Answer 7

when you override an sub class method visibility must be wider than parent class.

Wider to strict order:

public default protected private