Recently, I have intended to re-review the Java foundation. When I first sticked to the only relationship between the object, what is the interface of the object, just like a computer sales, she doesn't matter if the internal structure of the power supply, he is only the relationship can give you electricity. That is, just know if CAN or Not instead of How and why. All programs are composed of certain attributes and behavior objects, and different objects access through function calls, all exchanges between objects are called by way, By increasing the multiplexing rate in the package object data. 2. The most important idea inoo is class, class is a blueprint, constructed an object from the class, that is, an instance of this class (Instance) 3. Package: Just combine data and behavior in a package) and the implementation process of the object user hides the data, the data in an object calls his instance field (instance field) 4. By expanding a class to get one The new class is inheritance, and all classes are extended by Object root superclass, and the root super class will be introduced. 5. The 3 main features of the object beHavior --- Description This object can do. State --- Reflection of the object when the object is applied. Identity --- distinguishing between the other similar behavior objects. Each object has a unique INDENTITY and this is mutually influential. 6. The relationship between class: USE-A: Dependence HAS-A: Aggregation Relationship IS-A: Inheritance Relationship - Example: A Class A inherited Class B, at this time, Class A not only has Class B method, but also its own method. (Personality) Existence in commonality)
7. Construction object uses a constructor: The presentator is proposed, the constructor is a special method, constructing the object and initializes it. Example: Data class constructor called Data
New Data () --- Constructs a new object and initializes the current time.
Data happyday = new data () - The value assigns an object to a variable happyday, so that the object can be used multiple times, and the value of the variable and the object variable is different. NEW is one. Quote.
Constructor Features: The constructor can have 0, one or more parameters
The constructor and the same name have the same name
A class can have multiple constructors constructors without returning value constructors always used together with the New operator.
8. Overload: When multiple methods have the same name and contain different parameters, it is overloaded. The compiler must select which method of calling.
9. Package Java allows one or more classes to become a group, called packets to facilitate organizational tasks, standard Java libraries are many packages .java.lang java.util Java, NET, etc. It is all Java packages in the Java and Javax package.
10. Inherited Thoughts: Allow new classes on the basis of existing classes, when you inherit an existing class, then you have multiplexed the methods and fields of this class, and you can add it in the new class. New methods and fields.
11. Extended class: Extended class fully reflects the inheritance relationship of IS-A. Form is: Class (subclass) Extends.
12. Polymorphism: In Java, the object variable is polymorphically. Multiple inheritance is not supported in Java.
13. Dynamic Binding: Mechanism of calling an object method.
(1) The type and method name of the compiler check the object declaration.
(2) The compiler checks the parameter type called by the method.
(3) Static binding: If the method type is the Priavte Static Final compiler, which method will be accurately known.
(4) When a program is running and using a dynamic binding to call a method, then the virtual machine must call the method version of the actual type of object to which X points to the X.
(5) Dynamic binding: It is very important to make the program become scalable without need to recompile the filed code.
14.Final Class: In order to prevent some people from derived new categories from your class, this type is not expandable.
15. Dynamic calls have taken longer than static calls,
16. Abstract class: The class specified by one or more abstract methods must be defined as Abstract
Example: Public Abstract String GetDescripition
17. Each class in Java is expanded from the Object class.
18. Equal and toString methods in the Object class.
Equal is used to test whether an object is equal to another object.
TOSTRING returns a string representing the object, almost every class overloads the method to return the correct representation of the current state.
(TSTRING method is a very important method)
19. General programming: All values of any class type can be replaced with object class variables .20. An array list: ArrayList dynamic array list, is a class library, defined in the java.uitl package, can automatically adjust array size.
21. The getClass method in the Class class Object class returns an instance of the CKASS type. When the program is started, the class containing the main method will be loaded. The virtual machine should load all the classes he need, and each loaded class is loaded. the type.
22. Class class provides powerful functional reflection for programming programming that can dynamically manipulate Java code. This feature is especially useful for JavaBeans, using reflection Java to support VB programmers used to use tools. Campaign to analyze the ability to call reflectors The package of this feature in Java is very powerful in java.lang.Reflect reflex mechanism.
1) The ability to analyze class at runtime.
2). Objects in the runtime.
3). Implement universal array manipulation code.
4). Provide method objects.
This mechanism is primarily targeted by tools rather than applications and procedures.
The most important part of the reflective mechanism is to allow you to check the structure of the class. The API used by:
Java.lang.Reflect.field Returns the field. Java.Reflect.Method Returns the method. Java.lang.reflect.constructor Returns the parameters.
Method pointer: Java has no method pointer, passing the address of a method to another, can call it later, and the interface is a better solution.
23. Interface indicates what the class does not specify how to do it, and a class can implement one or more interface.
24. The interface is not a class, but a set of specifications for classes that meet the interface requirements.
If you need to implement an interface, you need 2 steps:
1). The specified interface that needs to be implemented.
2). Provide definitions of all methods in the interface.
Declare a class to implement an interface. You need to use the imports keyword Class Actionb IMPLEMENTS Comparable. It is necessary to provide a CompareTo method. The interface is not a class, and an interface cannot be instantiated with a New.
25. A class has only one superclass, but a class can implement multiple interfaces. An important interface in Java Cloneable
26. Interface and callback. Programming a common mode is a callback mode. In this mode you can specify a method on the callback object when a specific time occurs. Example: ActionListener interface monitors. Similar APIs are: java.swing. JOPTIONPANE JAVA.SWING.TIMER JAVA.AWT.Tookit
27. Object Clone: Clone method is Object a protection method, which means that your code cannot be simply call it.
28. Internal Class: Definition of an internal class is a class defined in another internal
The reason is: 1. An internal class object can access the implementation of the object that created it, including private data 2. For other classes in the same package, the internal class can hide. 3. Anonymous internal classes can be convenient Define the callback. 4. Use the internal class to be very convenient to write event drivers.
29. Proxy: 1. Specify the interface to require all the code 2.Object class definition (TSTRING Equals)
30. Data Type: Java is emphasized the type of language, each variable must first declare that it is type, there are 8 basic types in Java. 4 is integer, 2 is a floating point, one is a character type , Which is used in the Unicode encoding characters, Boolean.
Author / Source: Greatqsh
