Java之static作用的全方位总结

最新推荐文章于 2025-06-24 08:30:00 发布

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原文链接：https://www.cnblogs.com/gxyandwmm/p/9478569.html

参考https://www.cnblogs.com/gxyandwmm/p/9478569.html

1.static方法一般称作静态方法，由于静态方法不依赖于任何对象就可以进行访问，如testReslutSet()，代码如下：

package test_yanggang;

import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;
import java.util.logging.FileHandler;
import java.util.logging.Formatter;
import java.util.logging.Level;
import java.util.logging.LogRecord;
import java.util.logging.Logger;

public class test0918 {

   static SimpleDateFormat dateFormat = new SimpleDateFormat(
           "yyyy-MM-dd HH:mm:ss.SSS");
   static Logger logger = null;
   static FileHandler fileHandle = null;
   static {
       logger = Logger.getLogger("yangang");
       try {
           fileHandle = new FileHandler("yanggang.log");
       } catch (SecurityException e) {
           // TODO Auto-generated catch block
           e.printStackTrace();
       } catch (IOException e) {
           // TODO Auto-generated catch block
           e.printStackTrace();
       }
       logger.setLevel(Level.INFO);

       fileHandle.setLevel(Level.INFO);
       fileHandle.setFormatter(new Formatter() {// 定义一个匿名类
                   @Override
                   public String format(LogRecord record) {
                       return dateFormat.format(new Date()) + ":"
                               + record.getMessage() + "\n";
                   }
               });
       logger.addHandler(fileHandle);
   }

   public static void testReslutSet() throws Exception {
       Connection conn = null;
       Statement statement = null;
       ResultSet rs = null;

       String url = "jdbc:oracle:thin:@10.10.10.186:1521/orcl"; // 链接字符串
       String user = "bl_user"; // 数据库的用户名
       String password = "bluser_123"; // 数据库的密码

       //String url = "jdbc:oracle:thin:@192.168.197.119:1521:SCF"; // 链接字符串
       //String user = "SCF_PROD"; // 数据库的用户名
       //String password = "valin_2018"; // 数据库的密码
       try {
           Class.forName("oracle.jdbc.OracleDriver");
           // 1.获取Connection
           conn = DriverManager.getConnection(url, user, password);
           // 2.获取Statement
           statement = conn.createStatement();
           // 3.准备SQL
           rs = statement.executeQuery("select count(*) totalCount from jzl_user.m_po_measure_t@DBL_TO_JZL");

           //rs = statement.executeQuery("select count(*) totalCount from POUNDLISTM");
           int rowCount = 0;
           if(rs.next()) {
           rowCount=rs.getInt("totalCount");
           }
           logger.info("return row number from view m_po_measure_t: "
                   + rowCount + "");

       } catch (Exception e) {
           e.printStackTrace();
           logger.info("error: " + e.getMessage() + "");
       } finally {
           // 6.关闭结果集
           if (rs != null) {
               rs.close();
           }
           if (statement != null) {
               statement.close();
           }
           if (conn != null) {
               conn.close();
           }
       }
   }

   public static void main(String[] args) throws ParseException {
       // SimpleDateFormat dateFormat = new
       // SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");
       new Timer("testTimer1").scheduleAtFixedRate(new TimerTask() {
           @Override
           public void run() {
               try {
                   testReslutSet();
               } catch (Exception e) {
                   // TODO Auto-generated catch block
                   e.printStackTrace();
                   logger.info("error: " + e.getMessage() + "");
               }
           }
       }, new Date(), 300000);
   }
}
2.static代码块。形成静态代码块以优化程序性能，为什么说static块可以用来优化程序性能，是因为它的特性:只会在类加载的时候执行一次，如上面代码红色部分