The role of the Java keyword final and static

First, the keyword final

• Final Modified class: This class cannot be inherited
• Final modification method: cannot be overridden
• Final Decorated property: This property is a constant that cannot be assigned once initialized. In practice, constants are represented by uppercase characters.
• Where this constant is assigned: ① This constant cannot use the default initialization ② can be explicitly assigned, code block, constructor

Note: variables are modified with static final: Global Constants

Second, the key word static

Static, statically, can be used for properties, methods, * blocks of code (or initialization blocks), * inner classes

Static modifier property (class variable):

• All objects created by the class share this property
• When one of the objects modifies this property, it causes another object to make a call to this property. VS instance variable (non-static decorated property with each object owning a set of replicas)
• Static class variables are loaded with the load of the class, and the uniqueness
• Static variables can be called directly from the "class. Class variable" form.
• Static class variables are loaded earlier than the object. So when you have an object, you can use the object. Class variable. However, "class. Instance variable" is not possible.
• Static class variables exist in the static domain

Static Modification method (class method):

• Loaded with the load of the class, it is also unique in memory
• Can be called directly from the "Class. Class method" mode.
• You can call a static property or a static method internally, and you cannot invoke a non-static property or method. Conversely, a non-static method can call a static property or a static method

Note: Static structures (properties of static, methods, blocks of code, inner classes) have a lifetime earlier than non-static structures, and are recycled later than non-static structures

The static method inside is not allowed to have this or super keyword!

Static Test instance:

 PackageCom.yyx.pratice; Public classJavapratice { Public Static voidMain (string[] args) {account A1=NewAccount ("abc123", 1000); Account A2=NewAccount ("abc456", 2000); Account A3=NewAccount ("abc456", 2000);        SYSTEM.OUT.PRINTLN (A1);        SYSTEM.OUT.PRINTLN (A2);    SYSTEM.OUT.PRINTLN (A3); }}classAccount {Private intId//Account Number    PrivateString password;//Password    Private DoubleBalance//Balance    Private Static Doublerate = 0.05;//Interest Rate    Private Static DoubleMinBalance = 1;//Minimum Balance    Private Static intinit = 1000;  PublicAccount (String password,Doublebalance) {         This. id = init++;  This. Password =password;  This. Balance =balance; }     Public intgetId () {returnID; }     Public voidSetId (intID) { This. ID =ID; }     PublicString GetPassword () {returnpassword; }     Public voidSetPassword (String password) { This. Password =password; }     Public DoubleGetBalance () {returnbalance; }     Public voidSetbalance (Doublebalance) {         This. Balance =balance; }     Public Static Doublegetrate () {returnRate ; }     Public Static voidSetrate (DoubleRate ) {Account.rate=Rate ; }     Public Static Doublegetminbalance () {returnminbalance; }     Public Static voidSetminbalance (Doubleminbalance) {account.minbalance=minbalance; } @Override PublicString toString () {return"Account [id=" + ID + ", password=" + password + ", balance=" + Balance + "]"; }}

The role of the Java keyword final and static