1. Static modified classes can only be internal classes, and ordinary classes cannot be modified with the static keyword. The internal class modified by static is equivalent to an ordinary class, and the access method is (new external class name. internal class method()). As follows:
public class OuterClass {
public static class InnerClass{
InnerClass(){
System.out.println("============= I am an inner class'InnerClass' =============");
}
}
}
public class TestStaticClass {
public static void main(String[] args) {
// No need for a new InnerClass
new OuterClass.InnerClass();
}
}
Note: The access method of ordinary inner class is (external class object.new inner class method())
2. The access method of static modified static method is (class name. method name)
3. The difference between static variables and instance variables
Variables modified by static are static variables. Static variables have only one storage space in memory. Static variables do not belong to an instance object. They are shared by all objects in a class and belong to the class, so they are also called class variables and can be passed directly Refer to the class name.
Instance variables are private to a fixed object, the use of instance variables must first create an instance of the class, and then use this instance to reference.
public class Person {
int age = 10;
static int age1 =11;
}
public class Test {
public static void main(String[] args) {
Person person = new Person();
person.age=11;
person.age1 = 12;
Person person1 = new Person();
System.out.println(person.age);
System.out.println(person.age1);
System.out.println(person1.age);
System.out.println(person1.age1);
}
}
Results: 11
12
10
12
| static |
Static variable |
Static method |
| Alias |
Class variable |
Class method |
| level |
Same level as the class |
Same level as the class |
| load |
As the class is loaded, it is loaded into the static area of the method area |
As the class is loaded, it is loaded into the static area of the method area |
| Initial value |
Give the system default initial value |
Does not give the system default initial value, it will be loaded into the stack for execution when called |
| transfer |
1. Class name. 2. Object. |
1. Class name. 2. Object. |
|
|
Objects generated by the class can share the same static variable |
Support overload |
|
|
Static variables cannot be defined in methods (normal methods and construction methods) |
Does not support rewriting (rewriting is for objects) |
|
|
|
Static information in Java can only use static information directly |
|
|
|
But non-static information can directly use non-static and static |
5. The format of the static code block is:
public class class name { static { //content of the static code block } Features: When this class is used for the first time, the static code block is executed only once. Static content always takes precedence over non-static content, so static code blocks are executed before construction methods. Typical use of static code blocks: to assign values to static member variables at once.