Object-oriented - Encapsulated
1.1
Classes and Objects
1.1.1 Classes and objects understanding
Object: things in the world
Class: The class is an abstraction of reality a class of things with common attributes and behavior of
A collection of data objects is a type of object classes, attribute classes and having the same behavior
Simple to understand: The class is a description of the reality of things
The composition of the class
属性：事物的特征
行为：事物能执行的操作
The relationship between classes and objects: class is a thing of the description, the object was something concrete existence.
1.1.2 class definition:
Composition class is composed by the properties and behavior.
The class definition step:
① the definition of class
② writing a class member variables
③ writing a class member method
{public class name of the class
// Member variables
Variable 1 Variable Data type 1;
Variable data type of the variable 2 2;
…
// member method
method 1;
Method 2;
}
Sample Code
/*
Phone categories:
Class Name:
手机(Phone)
Member variables:
Brand (brand)
Price (price)
Member method:
Call (call)
Send text messages (sendMessage)
*/
public class Phone {
//Member variables
String brand;
int price;
// member method
public void
call() {
System.out.println("打电话");
}
public void
sendMessage() {
System.out.println ( "texting");
}
}
1.1.3 use objects
Create an object format:
Object class name name = new class name ();
Members call format:
Object name. Member variables
Object name. Member method ()
1.2
Object Memory FIG.
Those who are new things out of heap memory
Own member variables are as defined in the stack memory
1.3
member variables and local variables difference
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1.4
packaging and construction methods
1.4.1
private
private is a modifier, member (member variables, member method) can be used to modify
Modified members can only access this class. For class he used, the need for a corresponding operation.
1.4.2
this
this modified variable used to refer to members of the variable major role (duplicate names to distinguish local variables and member variables)
Shaped member variables involved in the same process, without this variable is modified parameter refers
this time: the hidden member variables to address local variables
this: object class representatives in your reference. (Which method is called an object, this object represents on which)
Different methods of participation shaped member variables, variables without this modification refers to the member variable
this represents the reference to the current method call, which object method call, which will this object represents
1.4.3
Packaging ideas
Package Overview
Is facing one of the three features of the object (encapsulation, inheritance, polymorphism) is an object-oriented programming language to simulate the objective world, the objective world, member variables are hidden inside the object, the outside world can not be directly manipulated
封装原则
Hiding certain information classes within a class, do not allow direct access to an external program, but is achieved by a method provided by the class of hidden information and the access operation member variables private, to provide the corresponding getXxx () / setXxx () method
Benefits Package
Member variable to the control operation by the method, improves the security code to code encapsulating methods to improve the reusability of code.
1.4.4 Constructor
Constructor is a special method
Role: to create objects Student stu = new Student ();
format:
{public class name of the class
Modifier class name (parameter) {
}
}
Function: The main target is to complete the initialization data
Create a constructor
If not defined constructor, the system will be given a default constructor parameters if no defined construction methods, the system will no longer provide a default constructor
Overloaded constructor
The self-defined parameterized constructor, also using no-argument constructor must write a no-argument constructor
Recommended use
In both cases, all written by hand no constructor parameters
Important features!
You can use parameterized constructor, as a member variable is initialized
Object-oriented - Inheritance
2.1 inheritance definition, pros and cons, super, visit Features
2.1.1 definitions
Inherited format
Format: public class subclass name parent name extend {}
Example: public class Extend Zi
Fu {}
Parent Class: it may also be referred to as a base class, the superclass.
Subclasses: the derived class
Inherit the characteristics of neutron class:
① subclass can have the contents of the parent class
② subclasses can also own unique content
2.1.2 inherited the pros and cons
Lee: improve code reusability and maintainability
Disadvantages: increase the coupling between classes, subclasses of the parent class changes also need to follow the changes, weakening the independence of the subclass
Using inheritance time:
Inheritance reflect the relationship: is a
Suppose method: two classes A and B, A is B is a B or a A, i.e., the presence of inheritance.
Example: apple and fruit, cats and animals, dogs and cats [XG1]
2.1.3 Inheritance Variable Access features:
Accessing a process variable in a subclass
Subclasses local area to find
Subclass members to find the range
Parent class members find range
If you are not on the error (without regard to his father's father [XG2] ...)
2.1.4 Super
Super similar keyword usage and this keyword
2.1.5 constructor inherited access features
The default constructor with no arguments have access to the parent class
2.1.6 Access member methods inherited characteristics
Access by a child class object Method
①子类成员范围找
② parent class members find range
③ If you are not on the error (without regard to his father's father ...)
2.2 The method of rewriting and overwriting method wherein Note
2.2.1 method overrides
Overview: subclass method declaration and the emergence of the parent class exactly the same.
Application: When required function subclass the parent class, subclass and main body have their own unique content, you can override the parent class method, so that followed the functionality of the parent class, but also defines the type of unique content.
@Override
Annotations can help rewrite the method of checking the correctness of the method statement
2.2.2 Notes
Private methods can not be overridden (subclass the parent class private members are not inherited)
Subclass method can not be less access to (public> Default> Private)
Notes 2.3 java inherited, package, import
2.3.1
in java inherited Notes
Only supports single inheritance, do not support multiple inheritance
Java class supports multiple inheritance
2.3.2
package
Modifiers
Package: in fact, folders,
Role: manage your classes
Definition Format:
Format: package package name; (coated with multi-stage; separately)
Example: package com.itheima; (Notepad)
2.3.3
import
Package guide: using different packet classes, the full path of the package used to write, to write too much trouble, in order to simplify the operation with a package, java package provides a guide function.
Format: import package name;
Examples: import cn.com.itcast.Teacher
2.4 permission modifier (private, protected, public), the state of the modifier (final, static)
2.4.1 Permissions modifier (private, protected, public)
2.4.2 state modifier (final, static)
final: members can be modified methods, member variables, classes
final modified features:
Modification method: the ultimate method show that this method can not be overridden
Modifying variables: indicates that the variable is constant and can not be assigned again
Modified class: class indicates that the class is final and can not be inherited
final modification of local variables:
Basic type: modified data value change can not occur
Reference types: modified address value changes can not occur, the address where the content can be changed
static: members can be modified methods, member variables
static modification features:
被类的所有对象共享（这也是我们判断是否使用静态关键字的条件）
可以通过类名调用，也可以通过对象名调用，推荐使用类名调用
static access features; static member methods can only access static member methods.
Object-oriented - Polymorphism
More than 3.1 state
3.1.1 Polymorphism
The same object, manifested at different times different tenses
Example: Cat
It can be said is a cat a cat: Cat cat = new Cat ();
It can also be said that the cat is an animal: Animal animal = new Cat ();
Cat show up at different times in different forms, this is polymorphism.
Polymorphic premise and reflect
Inheritance / implementation relationship
There are ways to rewrite
There are references to parent child class object
3.1.2 polymorphic members access features:
Member variable: Compile look left, look left execution
Member method: Compile look left, look to the right of execution
Access is not the same reason: the members have to rewrite the method, but no member variables
3.1.3 Benefits and drawbacks
Benefits: improve program scalability
具体体现：定义方法的时候，使用父类型作为参数，将来在使用的时候，使用具体的子类型参与操作。
Drawbacks: You can not use function-specific subclasses
3.1.4 Transition
① upward transition
从子到父
父类引用指向子类对象
② downcast
从父到子
父类引用转为子类对象
3.1.5 abstract class
Java, a method is no method body should be defined as abstract methods, whereas if there is an abstract method, the class must be defined as an abstract class.
Abstract class features:
Abstract classes and abstract methods must be modified to use the abstract keyword
public abstract class类名{}
public abstract void eat();
Abstract classes are not necessarily abstract methods, a method of abstract class is an abstract class must
An abstract class can not be instantiated
How abstract class to instantiate it? Referring polymorphic manner, by subclass object instantiated abstract class called polymorphism
Subclass of abstract class
Either override all abstract methods abstract class
Or is an abstract class
Features abstract class members
Member variables (variables can also be a constant)
Construction method
The method has a structure, but can not be instantiated
So, what is the role of the constructor is it? Subclasses for initializing the access to the parent class data
Member method
Can abstract methods: defining a subclass must complete certain actions
There may also be a non-abstract methods: improve code reusability
3.2 Interface
3.2.1 interface and its features, features members
Interface Overview:
Interface is a kind of common standards, they meet the standards, you can use
Java interface in more reflected in the behavior of the abstract
Features Interface
Interface with the keyword interface modification
public interface 接口名{}
Represented by class implements the interface implements
public class类名implements接口名{}
Interfaces can not be instantiated
Interface how to instantiate it? Referring polymorphic manner, by implementing the class of the object instance, the interface is called polymorphism.
Polymorphic forms: polymorphic concrete class, an abstract class of multi-state, multi-state interfaces
Polymorphic premise: inheritance relationship or implement; the method of rewriting; the parent (Class / Interface) reference point (promoter / implement) class object
Interface implementation class
All abstract interface methods either rewrite
Or is an abstract class
Members of the interface features
Member variables
Only constant
The default modifier: public static final
Construction method
Interface no constructor, because the interface is mainly to conduct the abstract, there is no specific
If a class has no parent, the default inherited from class Object
Member method
Only abstract methods
The default modifier: public abstract
3.2.2 The relationship between classes and interfaces
The relationship between class and class
Inheritance, only single inheritance, single inheritance may multilayer
Relationship classes and interfaces
Relationship to achieve, can be a single implementation can also be implemented multiple, multiple interfaces may also be implemented at the same time a class inheriting
Interface and its relationship
继承关系，可单继承，也可多继承
The difference between abstract classes and interfaces 3.2.3
An abstract class is an abstraction of things, and the interface is an abstract behavior
3.2.4 class name as parameter and return value
Parameter is the name of the class method, in fact, need is the object of the class
The return value of the method is the class name, in fact, the return of objects of the class
3.2.5 Abstract class name as a parameter and return value
Shape parameter method is an abstract class name actually needed is an object of the subclass of abstract class
The return value of the method is an abstract class name, in fact, returns the class object is a child character abstract class
3.2.6 Interface name as parameter and return value
The method parameter is the name of the interface, in fact, it needed to achieve the object of the class interface
The return value is the interface method name, in fact, is to achieve the return of the interface class object
3.3 Internal class
3.3.1 Internal class
Internal class: defines a class in a class
Internal class definition format
format
{public class name of the class
修饰符class类名{
}
}
example:
{public class name of the class
public
class Inner{
}
}
Features like internal access
You can directly access the internal class members outside of class, including private
To access the external members of the class within the class, you must create an object
3.3.2 members of the inner class
Just a note, the members of the class to create objects using internal format
Format: external name class class internal
object name = internal external object class object.
3.3.3 partial inner class
Local inner class is defined in the method in the class, so the outside world can not be used directly, we need to create objects in internal methods and use
Such members can directly access the external class, the method can access local variables
3.3.4 anonymous inner classes
Provided: the presence of a class or interface, where the class may be a particular class may be an abstract class
format:
new class or interface name () {
重写方法;
}
example:
new Inter(){
public void show(){
}
}
Nature: an inherited class or subclass that implements this interface anonymous object
[XG1] such a relationship should not use inheritance
[XG2] happen will complain