private static ClassName ClassInstanceVariableName = null; .....这是什么？

Question

那么这里有一个静态实现,我不明白.我以前使用静态但不广泛,任何人都可以帮助我理解代码.这是代码

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;


public class Connection_Class {
String driver_ClassName="com.mysql.jdbc.Driver";
String URL_connection="jdbc:mysql://localhost:3306/vendor";
String user="root";
String password="lifesuckzz";
   //can anybody explain what the following line means, especially the static part.......
    private static Connection_Class connectionclass=null;

private Connection_Class(){
    try{
        Class.forName(driver_ClassName);

    }catch(ClassNotFoundException e){
        e.printStackTrace();
    }
}

public Connection getConnection() throws SQLException{
    Connection con=null;
    con=DriverManager.getConnection(URL_connection,user,password);
    return con;
}

public static Connection_Class getInstance(){
    if(connectionclass==null){
                 //I know its returning an instance here
        connectionclass=new Connection_Class();
    }
    return connectionclass;
}


}

Answer 1

static表示变量是类本身的成员(只有一个副本),而不是类的对象成员(每个对象一个).您可以在static没有对象的情况下访问变量.在这种情况下,您可以调用Connection_Class.getInstance()以获取Connection_Class整个程序共享的单个对象.