JAVA-function overloading and overriding __linux

1. Function overload (overloding)

concept: a function with the same name has a different argument list.

function: to achieve the internal polymorphism of a single class, is static polymorphism.

Note the point:

(1) There is at least one difference in the type, number and order of the parameters.

(2) cannot overload by access permission , return type , thrown exception .

2. Function rewrite (overrideing)

Concept: defining a method in a subclass with the same name and parameters as its parent class, or when the parent class reference of a subclass object uses this method, invokes the definition in the subclass.

function: to achieve polymorphism in inheritance is the manifestation of polymorphism between parent class and subclass.

Note the point:

(1) The method name, parameter, and return value must be the same.

(2) The subclass method cannot narrow the access rights of the parent class method.

(3) A subclass method cannot throw more exceptions than the parent class (subclasses can not throw exceptions).

(4) A method that is defined as final cannot be rewritten.

3 .  the principle of whether an object reference can invoke a method

(1) Upward transformation: The subclass is transformed into the parent type.

(2) Subclass object reference: A method can be invoked if it exists in a subclass definition, otherwise it cannot be invoked.

(3) Parent class object reference: The method exists in the parent class definition can be invoked, the invocation result is based on the polymorphism principle, otherwise it cannot be invoked.

Animal class Public class Animal { Public void introduce () { System.out.println ("I am an animal!"); } } Cat class Public class Cat extends Animal { Rewrite the introduce of the parent class to implement the overriding Public void introduce () { System.out.println ("I am a cat!"); } Realized the overloading Public void Introduce (String name) { System.out.println ("I am a cat, my name is:" + name); } } Dog class Public class Dog extends Animal { Rewrite the introduce of the parent class to implement the overriding Public void introduce () { System.out.println ("I am a dog!"); } Realized the overloading Public void Introduce (String name) { System.out.println ("I am a dog, my name is:" + name); } } Test class Public class Test { Public Static void Main (string[] args) { Overriding is a manifestation of polymorphism between the parent class and the subclass Animal animal1 = new Animal (); Animal Animal2 = new Cat (); Animal Animal3 = new Dog (); Animal1.introduce (); Animal2.introduce (); Animal3.introduce (); Animal2.introduce ("JACK"); It's the wrong use. Animal3.introduce ("JACK"); It's the wrong use. Overloading is the embodiment of polymorphism in a class Cat cat = new cat (); Cat.introduce (); Cat.introduce ("JACK"); } } The results of the operation are as follows: I am an animal! I am a cat! I am a dog! I am a cat! I am a cat, my name Is:jack