if a method is overloaded, does it still inherit the original method from the parent class? What about overriding? Would it also inherit the original plus the overridden one?
if a method is overloaded, does it still inherit the original method
from the parent class?
Yes, you can use both of them.
What about overriding? Would it also inherit the original plus the
overridden one?
Again - yes, but in this case to access the original method you'll have to use a call super.originalMethod().
if a method is overloaded, does it still inherit the original method from the parent class?
yes.
What about overriding?
yes, but the overidden method is not accessible to other classes.
Would it also inherit the original plus the overridden one?
yes.
In case of overloading, the method in the parent class is still available in the child class.
In case of overriding, the method doesn't run the parent's version unless explicitly called using super.method().
Related
If you write a class that you intend for others to extend but have ONE method that you don't want overridden by those subclasses, how could you do this?
Adding a final modifier to a method, class, or variable means it can't be extended or changed.
https://docs.oracle.com/javase/tutorial/java/IandI/final.html
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?
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.
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.
When you override any method, the visibility of the override must be at least as visible as the base method.
When you override any method, the visibility of the override must be equal or more than the visibility of the base method
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.
Because you are overriding a method, you must define it as the prototype method or more than that.
when you override an sub class method visibility must be wider than parent class.
Wider to strict order:
public
default
protected
private
What is the difference between abstract methodand method overriding in java? Because same result can be found by using method overriding. so what is the necessity of abstract method.
An abstract method forces a programmer who inherits the method to define an implementation for it, i.e. the class says "I will need an implementation of this function, which the concrete implementation of this class must provide".
This is in contrast to overriden methods, which allow (rather than require) the inheriting class to change the implementation of the method for objects of that class.
In particular, overridable methods (or "virtual" methods) have a basic implementation (which can itself be empty) that the overriding method can call.
The abstract method needs to be implemented in order for the subclass to be utilized. You must also implement non-abstract methods, for instance, in the case of interface method signatures.
I think it is correct to say that you implement abstract methods in the same way that you implement method stubs of an interface. Overriding is not the same as implementing because you can override methods which are not stubs. Subclasses often override methods where the superclass is neither an interface nor an abstract class. So the term overriding has a broader meaning than implementation.
You may find this tutorial helpful as it has quite a clear definition.
http://docs.oracle.com/javase/tutorial/java/IandI/abstract.html
Hope that helps!
The two have different usages which can't be compared.
An Abstract Class is created only to be sub classed by some other class. The implementing class necessarily has to implement all the abstract methods declared inside it. However Method Overriding is the ability of a subclass to override a method from an inherited superclass whose behavior is "close enough" and then to modify behavior as needed. An Abstract Method is one that is declared without an implementation and needs to be necessarily implemented in the subclass.
When the parent class have an add method with 2 parameters, If we add new add method with 3 parameters in child class, shall we call this as over loading?
Thanks in advance.
Yes, since the method with two parameters is inherited by the subclass, the method with three parameters is said to be an overloading method.
class A
add(param1, param2)
class B
add(param1, param2) <-- inherited
add(param1, param2, param3) <-- overloading the above method
A quote from the official trail on Overriding and Hiding Methods:
Note: In a subclass, you can overload the methods inherited from the superclass. Such overloaded methods neither hide nor override the superclass methods—they are new methods, unique to the subclass.
(As you probably already figured out, the method with three classes is not an overriding method.)
Yes, this is overloading. It would be overloading even if the method were in the same class as the method with two parameters.
Note that when there are different numbers of parameters (and no varargs parameters) overloading is reasonably simple. It gets a lot more complicated when you have methods with the same number of parameters - at that point the compiler has to choose the "best" method out of applicable candidate methods.
Also note that overloading is determined at compile time whereas which override is executed is determined at execution time based on the actual type of the object the method is called on.
Overloading is when methods have the SAME NAME but DIFFERENT SIGNATURE.
Overriding - when methods have IDENTICAL NAMES and IDENTICAL SIGNATURE.
Yes definitely a overloading and a nice feature of inheritance.
If the method name already exists but the parameters are different, then yes, this is overloading.
yep... it is overloading method even if the method is located in the same class.
ps: i assume the new method with three parameters has identical name and return type
This is a very naiveish question, but here goes:
An overriden method from a base class will mean that calls to the sub class will call the derived, overriden method, correct?
Thus, if there is no override annotation, the method in the base class will be called. So the override method will serve purely to document the intent - call one version of a method over the other.
Is this the case?
This leads me to the following question:
What is the difference between an abstract class which 5-6 classes may derive from but the methods inherited in the derived classes are not overriden, and one class (Static or not being irrelevant), used by those 5-6 classes?
The #Override annotation is intended ONLY to catch errors at compilation time. It does not affect override behavior at runtime. The idea is that you give the compiler the chance to inform you that your method name or signature is wrong.
The override annotation is simply a marker to show the the method overrides a superclass method.
It being there has no effect at runtime. See here:
http://download.oracle.com/javase/1.5.0/docs/api/java/lang/Override.html
Using abstract is an architectural design to ensure that users either must implement an abstract method (declared but not implemented in the base class) or that they all have access to the same base methods and data (this is the same as the latter example you gave).
Thus, if there is no override
annotation, the method in the base
class will be called.
No. The overriding method in the derived class will always be called.
So the override
method will serve purely to document
the intent - call one version of a
method over the other.
Is this the case?
No. As per the other answers, it tells the compiler to insist that there was something to override.