java foundation
Eight basic data types: byte short int long float double char boolean;
Reference Type: Array interface class basic data and reference types may all be received as a variable receipts
Variables can only receive a data
Constant: Once the amount can not be correctly modified is the constant.
Operators commonly used relational operators, logic operators, like arithmetic operators.
Array: As a variable can only store so we can use the time saved in an array of multiple data
array of tools sort method can be easily sorted to the array
String String is a special data type is a class (each also corresponds to a basic type class)
String bottom layer is an array of char
We can use the string class method to add the string. Remove Comparative Alternatively. Segmentation operation
Use StringBuffer class can save more resources in string concatenation.
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Senior Java
Relationship with the object class: class is abstract object, the object is an instance of the class
Class contains the properties and methods.
We can use access modifiers: public private protection to determine access rights
Commonly used modifiers are pubilc and private
Package: members of the class is private can use the package to be exposed to the outside packaging can make the property more secure.
Methods: a function of a method.
There are common methods, constructors, overloaded methods, override methods, abstract methods, static methods
Common method is a general method
Constructor methods named classes generally used to initialize the property
Overloaded methods, because the same method name and therefore programmers to call. Note overloaded methods must be different parameters
Abstract method, only present in the abstract modification abstract class, the method also requires use abstract modification
An abstract class can have both abstract methods may also have a physical method.
Overriding methods. The method of rewriting occurs it means that polymorphism occurs.
With reference to a different subclass object reference. Polymorphism is the
That is a subclass overrides a parent class, polymorphism occurs only in succession
Inherited need to use extends the parent class name after the name of the class to inherit the parent class
If the parent class is abstract. All you need is a method to the class
The right of inheritance, in addition to inheriting class can inherit interface. Interface
Of which only an abstract method, thus inherits the interface, you also need real
Now all of the interface methods. Distinction is an abstract class interface, pumping
Can have a physical method, only an abstract interface method as classes. Class
Inherit a class can only inherit in java, but can inherit multiple interfaces
So you can use the java interface multiple inheritance.
Static properties and methods do not return all the objects. Existed and when the class is loaded
And only one, can only use the class name method name or class name in memory. Attribute name
To call, (according to different development tools can also be called an object)
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Java exception mechanism of five keywords try ... catch to catch the exception
Or use this method throws an exception may occur in parentheses after the method declaration
Exception to the caller to deal with. That is the call of the try ... catch
finally keyword as long as there will be executed. Regardless of whether the program is running correctly
thorw can define their own throw, only three common, general use
try ... catch capture handle the exception, or throws an exception is thrown ..
In the memory array using an array of things when due to length restrictions, often can not meet
Demand. Thus, if a collection of commonly used list set and map collections
The method can be used with a set of many. Powerful and can be installed in any type of data
Because the collection can hold any type of data so the data set is unsafe.
So we used a generic collection. Will determine the type of data stored in the custom collection
This ensures data security.
Whether variables, arrays or collections, can only temporarily store variables, so we need to use
IO stream data stored in a file. This can be done permanently store data stored in the data
Because txt text cumbersome to operate and not intuitive
Therefore, we use XML to save the file, the benefits of XML documents is that he is not limited to any of
Platform, language and system, can easily exchange data and call data in different environments
But later we will use the database to store data.
Network Programming and multithreading
Socket network programming primarily for data exchange between computers
That is, data exchange and data between the client and the server share
Process is the system resources and space applications in the system independently owned
CPU scheduling thread is dispatched and the base unit, the order can be completed independently
Control flow, a thread to complete a project.
Run multiple threads in the same process is multi-threaded.
Multithreading is not really running multiple tasks at the same time but multiple threads
Alternately CPU resources. But because the process is very fast and therefore feel
Simultaneously. Multithreading can make full use of CPU resources, simplified programming model