Final and Static keywords for the Java Foundation

Source: Internet
Author: User

First, Final
Depending on the context of the program, it can modify non-abstract classes, non-abstract class member methods, and variables. The final class cannot be inherited, there are no subclasses, and the methods in the final class are final by default.
The final method cannot be overridden by a method of a class, but can be inherited.
The final member variable represents a constant, which can only be assigned once, and the value will no longer change after the value is assigned.
Final cannot be used to modify a construction method.
Note: The private member method of the parent class is not overridden by the class method, so the private type method defaults to the final type. 1. Final class
The final class cannot be inherited, so the member methods of the final class have no chance of being overwritten, and the default is final.  In the design class, if the class does not need to have subclasses, the implementation details of the class are not allowed to change, and it is certain that the class will not be extended, then it is designed as the final class. 2. Final method
If a class does not allow its subclasses to overwrite a method, you can declare this method as the final method.
There are two reasons for using the final method:
First, lock the method to prevent any inherited classes from modifying its meaning and implementation.
Second, efficient.  The compiler goes into an inline mechanism when it encounters a call to the final method, greatly improving execution efficiency. 3. Final variable (constant)
A constant is represented by a final modified member variable, which cannot be changed once the value is given!
There are three final modified variables: Static variables, instance variables, and local variables, representing three types of constants, respectively.
As you can see from the example below, once the initial value is given to the final variable, it cannot be changed.
In addition, when the final variable is defined, it can be declared without giving the initial value, which is also called the final blank, and in any case the compiler ensures that the blank final must be initialized before it is used.  However, final whitespace provides greater flexibility in the use of the final keyword final, so that the final data members in a class can be implemented differently depending on the object, but with the same characteristics that remain constant. 4. Final parameters
When the function parameter is the final type, you can read it using the parameter, but you cannot change the value of the parameter. Second, static
Static represents the meaning of "global" or "static", which modifies member variables and member methods, and can also form statically static blocks of code, but there is no concept of global variables in the Java language.
member variables and member methods that are modified by static are independent of any object of the class. That is, it does not depend on class-specific instances and is shared by all instances of the class. As long as this class is loaded, the Java virtual machine can find them based on the class name in the method area of the run-time data area.         Therefore, a static object can be accessed before any of its objects are created, without referencing any objects. A static variable can have a private adornment before it, indicating that the variable can be used in a static block of code for a class, or in other static member methods or non-static member methods of a class, but it is important that it cannot be directly referenced in other classes through the class name. In fact, you need to understand that private is the access permission limit, static means do not instantiate can be used, so it is easier to understand more.         Static plus other access keyword effects and so on. The static modified member variables and member methods are customarily referred to as static variables and static methods, which can be accessed directly through the class name, and Access syntax is:
Class name. static method Name (parameter list ...)
The class name. The static variable name represents a static code block with a static-decorated code block, which is executed when the Java Virtual Machine (JVM) loads the class. 1. Static variables
There are two ways to classify a class member variable statically: A variable that is statically modified, called a static variable or a class variable, and another variable that is not modified by static, called an instance variable. The difference between the two is:
For static variables there is only one copy in memory (memory saving), the JVM allocates only one memory at a time, completes the memory allocation of static variables during the loading of the class, can be accessed directly (conveniently) by the class name, and, of course, is accessible through objects (but this is not recommended).
For instance variables, when an instance is not created, the instance variable is allocated one memory, and the instance variable can have multiple copies in memory without compromising (flexibility). 2. Static method
Static methods can be called directly from the class name, and any instance can also be called, so a static method cannot use the This and Super keywords, and cannot directly access the instance variables and instance methods of the owning class (that is, member variables and member methods without static). Only static member variables and member methods of the owning class can be accessed. Because instance members are associated with specific objects! This need to understand, want to understand the truth, not the memory!!!
Because the static method is independent of any instance, the static method must be implemented, not abstract. 3. Static code block
A static block of code is also called a code block, which is an independent block of static blocks in a class that is separate from a class member, can have more than one position, it is not in any method body, and the JVM executes these static blocks of code when the class is loaded, and if there are multiple static blocks of code, The JVM executes them sequentially in the order in which they appear in the class, and each code block is executed only once. 4. What does static and final piece mean?
Static final is used to modify member variables and member methods, which can be simply understood as "global constants"!
For variables, this means that once a value is given it cannot be modified and is accessible through the class name.
For methods, the representation is not overwritten and can be accessed directly through the class name. It is important to note that for instance constants that are static and final modified, the instance itself can no longer be changed, but for instance variables of some container types (for example, ArrayList, HashMap), the container variable itself cannot be changed, but the object stored in the container can be modified.  This is a lot of programming. Objects that are "loaded" in a variable of a container type through the static final modification can be changed.

Final and Static keywords for the Java Foundation

Related Article

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: info-contact@alibabacloud.com and provide relevant evidence. A staff member will contact you within 5 working days.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

  • Sales Support

    1 on 1 presale consultation

  • After-Sales Support

    24/7 Technical Support 6 Free Tickets per Quarter Faster Response

  • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.