final and static keyword in Java [Java]

0 , Overview

final keyword indicates that is immutable;

The following were the described attributes (fields), the method, the class;

1 , the attribute (or field), denotes a constant

In the final declaration attribute (or field), a denotes a constant, there are two methods to initialize, a declaration is initialized directly, like this static constant, it is determined at compile time; 2 is initialized in the constructor, this is its value is determined at runtime; sample code is as follows:

   public  class Man 
   { 
        Final String the Name = "John Doe";   // 1, constant declaration initialized with static 
        Final String EnName; 
       
        / ** 
         * constructor 
         * / 
      public Man () 
     { 
        EnName = "Anson";   // 2, in the constructor initializes, its value is determined until run 
      }   
   }

 

2 , Final method, the method can not be covered represents

The main role of the final method has two aspects: one is to prevent any derived class override methods . 2 is a more efficient program execution . After a method is set to final, the compiler will ignore conventional method to insert the code to perform the method call mechanism taken (the independent variable onto the stack; skip method code and execute it; jump back; clear the stack arguments; and finally processing the return value). It will replace the method call with a copy of the method within the body of the actual code. This can avoid the overhead of method calls to a certain extent.

Sample code is as follows:

class Man 
{ 
    / **  
    * Final methods can not override 
    * /  
    public  Final  void the Run () 
     { // ...} 
}

 

3 , Final class that represents the class can not be inherited

Final declaration of the class, the class can not be inherited represents; sample code is as follows:

final class Human 
 { //... }

 

 

000-static

About static, is better understood, do not write code example, there are four main uses: summarized as follows:

1. Used to modify a member variable, it becomes a member of the class, in order to achieve all the objects for sharing the member;
2. The method used to modify members, to turn it into a class method, you can directly use the " class name . Method name " way calling, commonly used tools;
3. Use static block, a plurality of members based on initialisation, to initialize static member;
4. Static bag usage guide, the class method directly into the current class, which directly use the " method name " to call the class method is more convenient, such as:

5. import static com.anson.utils.PythonHelper.*;