"Learning Notes" Java Object-oriented advanced programming 1

Content includes:

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Packaging
Analysis of problems caused by inheritance and use of inheritance
Variable hiding and method rewriting

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I. Encapsulation

Encapsulation via get and set

Here's a tip: choose quick and Efficient methods with shortcut ALT + Shift + 3, choose get and set for quick creation, with the following code:

 PackageCom.jfu.one; Public classPackage {Private intDog; PrivateString Cat;  Public intGetdog () {returnDog; }     Public voidSetdog (intdog) {         This. Dog =Dog; }     PublicString Getcat () {returnCat; }     Public voidSetcat (String cat) { This. cat =Cat; }     Public Static voidMain (string[] args) {}}

Two. Inheritance

Function: The reuse of code can be achieved through inheritance.

Java does not support multiple inheritance.

Subclasses can inherit the variables and methods of the parent class, except for private.

Create a subclass of a class by adding the extends clause to the declaration of the class:

class extends Superclass () {    }

Examples are as follows:

Car is the parent class, Smallcar inherits car for subclasses, and BMW inherits Smallcar

Car.java

 Package Carry;  Public class Car {    int price ;     Private String color;      Public Static void print () {        System.out.println ("Parent Car");}    }

Smallcar.java

 Package Carry;  Public class extends Car {        void  Smallcar () {            System.out.println ("This one small car class");    }          Public Static void Main (string[] args) {        new  Smallcar ();        Smallcar.print ();    }}

Bmw.java

 Package Carry;  Public class extends smallcar{    publicstaticvoid  main (string[] args) {        new  BMW ();        Bmw.print ();        Bmw.smallcar ();    }}

Running Bmw.java, the results are as follows:

Parent car This one small car class

Results Analysis:

In Bmw.java, this class inherits the Smallcar class, and the Smallcar class inherits from the car class, so the BMW class can use the properties and methods of the Smallcar class and car.

Three. Variable hiding in succession and method overloading principle

Variable hiding principle:

The variable name in the subclass is the same as the variable name that inherits from the parent class, and the variables that inherit from the parent class are hidden.

Method Rewrite principle:

1. Must have an inheritance relationship

2. The overridden method cannot have more restrictive access rights than the overridden method, which can be the same.

3. After rewriting the weight in the method can not be specific to the method to generate more exceptions (exceptions).

4. Return value, method name, method must have the same number of arguments as the parent class. (That is, only modify the contents of the inside, the other can not be changed!)

Animal.java

 Package OverWrite;  Public class Animal {    publicvoid back () {        System.out.println ("Animal is speaking");}    }

Dog.java

 Package OverWrite;  Public class extends Animal {        // method overrides public    void back () {        System.out.println ("The dog is Talking")    ;        }  Public Static void Main (string[] args) {        new  Dog ();        Dog.back ();    }}

Execution Result:

The dog is talking.

"Learning Notes" Java Object-oriented advanced programming 1