The difference between static keyword and final keyword in java

Author：Eve Cole Update Time：2024-11-19 09:24:01

static

1. In a class, attributes modified with static are called static attributes. It is common to all objects of this class and is stored in the static storage area. All objects of this class can access and access the same variable. Can be used as a counter to count how many objects of various types have been created in total.

2. In a class, the method modified with static is a static method. Non-static properties and methods cannot be accessed in a static method, but static methods and properties can be accessed in a non-static method; and the static method polymorphism is invalid and cannot Use this.

3. Since static properties and methods belong to all objects of this class, they can be accessed using class name.static property/method name---.

4.static can also modify the code block, which will be executed once and only once when the class is loaded.

final

(1) Classes marked final cannot be inherited

Copy the code code as follows:

final class T{}

class TT extends T{}//Error, final class cannot be inherited

(2) Methods marked final cannot be overridden by subclasses

Copy the code code as follows:

class T{

public final void function(){}
}

class TT extends T{

public void function(){}//Error, final method cannot be overridden by subclasses
}

(3) Local variables marked final are constants

Copy the code code as follows:

final int x=10;
x=3//Error, the local variable marked final is a constant and cannot be assigned a value

(4) Member variables marked final must be assigned a value at the same time as they are declared, or assigned explicitly in the constructor of the class (instance variables have no default values) before they can be used.

like:

Copy the code code as follows:

class Test{
final int x=10;//Declaration and assignment

}

//or

class Test{
final int x;
Test(){
x=10;

}

(5) The built-in class defined in the method can only access the final type local variables in the method. The local variable defined with final is equivalent to a constant, and its life cycle is longer than the life cycle of the method running.

(6) It is also possible to define a formal parameter as final, which limits the value range of the formal parameter that can be modified in the method.

There are many classes in java that are final types: String, Math, etc.