java keyword static

Link Address: http://www.cnblogs.com/devinzhang/archive/2011/12/13/2286367.html

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.

Static member variables and member methods that are decorated with public are essentially global variables and global methods, and when declaring the object city of its class, do not generate a copy of the static variable, but all instances of the class share the same static variable.

The static variable can have a private adornment before it, indicating that the variable can be used in the static code block of the class, or in other static member methods of the class (which can also be used in non-static member methods-nonsense), but it is important that the class name cannot be referenced directly in other classes. 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 ...)
Class name. Static variable Name

A static code block is represented by a statically decorated block of code that executes when the Java Virtual Machine (JVM) loads the class (very useful, hehe).

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, each time an instance is created, the instance variable is allocated one memory, and the instance variable can have multiple copies in memory, with no effect (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. For example:
public class Test5 {
private static int A;
private int B;

static{
Test5.a=3;
System.out.println (a);
Test5 t=new Test5 ();
T.F ();
t.b=1000;
System.out.println (T.B);
}
static{
test5.a=4;
System.out.println (a);
}
public static void Main (string[] args) {
TODO automatically generate method stubs
}
static{
test5.a=5;
System.out.println (a);
}
public void F () {
System.out.println ("Hhahhahah");
}
}



Operation Result:
3
Hhahhahah
1000
4
5

Static code blocks allow you to assign values to some static variables, and finally take a look at these examples, all in a static Main method, so that the JVM can be called directly without creating an instance when it runs the main method.

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.

Category: Java basics

java keyword static