How to use static in java

There is this passage on page P86 of "Java Programming Thoughts":

"A static method is a method without this. Non-static methods cannot be called inside a static method, and the reverse is possible. And it can be called inside a static method. Without creating any objects, the static method is only called through the class itself. This is actually the main purpose of the static method."

Although this paragraph is just an explanation The special features of the static method can be seen, but the basic function of the static keyword can be seen. In short, the description in one sentence is:

It is convenient to call (method/variable) without creating an object. ).

Obviously, methods or variables modified by the static keyword do not need to rely on objects for access. As long as the class is loaded, it can be accessed through the class name.

static can be used to modify class member methods and class member variables. In addition, static code blocks can be written to optimize program performance.

static method

static method is generally called a static method. Since static methods can be accessed without relying on any object, for static methods , there is no this, because it is not attached to any object. Since there is no object, there is no this. And due to this feature, non-static member variables and non-static member methods of the class cannot be accessed in static methods, because non-static member methods/variables must rely on specific objects before they can be called.

But it should be noted that although non-static member methods and non-static member variables cannot be accessed in static methods, static member methods/variables can be accessed in non-static member methods.

A simple example:

In the above code, since the print2 method exists independently of the object, you can Call directly using the class name. If non-static methods/variables can be accessed in static methods, then if there is the following statement in the main method:

MyObject.print2();

There are no objects at this time, str2 does not exist at all, so a contradiction will arise. The same is true for methods. Since you cannot predict whether non-static member variables are accessed in the print1 method, accessing non-static member methods in static member methods is also prohibited.

For non-static member methods, there is obviously no restriction on accessing static member methods/variables.

Therefore, if you want to call a method without creating an object, you can set this method to static. Our most common static method is the main method. As for why the main method must be static, it is now clear. Because the program does not create any objects when executing the main method, it can only be accessed through the class name.

static variable

static variable is also called a static variable. The difference between static variables and non-static variables is that static variables are shared by all objects and are stored in memory. There is only one copy, which is initialized if and only if the class is first loaded. Non-static variables are owned by objects and are initialized when the object is created. There are multiple copies, and the copies owned by each object do not affect each other.

The initialization order of static member variables is initialized in the order in which they are defined.

private static int i=0;

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