今天girlfriend到公司交作业(还是培训期),她们的pm让她们在数据读取的使用for循环(如例test1),问之,为啥,说pm说了,这样好,还拿了一本pm给的effective java,说看了就明白,废话不多说,看之,原来就这样一条,如果在循环体外不需要继续使用的变量建议使用for循环,并且在for的第一部分初始化,这样一来循环结束以后就会自动回收,但是大家仔细思考一下,这地方能利用这条原则??,resultset
是跟着statement走的,当你关闭statement,resultset会被关闭,使你使用for循环没有任何好处,相反,while要更快,使用for是弄巧成拙.例子如下,大家也看到while要比for快将近3倍,记录为1000条左右.写这个例子,希望大家不要犯类似的错.....
package jp.gibraltar.bnas.branch.accountclose.closecheck;

import java.sql.connection;
import java.sql.resultset;
import java.sql.sqlexception;
import java.sql.statement;
import java.util.vector;

import jp.gibraltar.util.dbutil;
import junit.framework.testcase;

/**
 * @author sfluo
 *
 * todo to change the template for this generated type comment go to window -
 * preferences - java - code style - code templates
 */
public class closecheckinputactiontest extends testcase {

 public static void main(string[] args) {
  junit.textui.testrunner.run(closecheckinputactiontest.class);
 }

 /*
  * @see testcase#setup()
  */
 protected void setup() throws exception {
  super.setup();
 }

 /*
  * @see testcase#teardown()
  */
 protected void teardown() throws exception {
  super.teardown();
 }

 public final void testexecutecheckinput() {
  closecheckinputactiontest test = new closecheckinputactiontest();
  system.out.println(system.currenttimemillis());
  test.test1();
  system.out.println(system.currenttimemillis());
  test.test2();
  system.out.println(system.currenttimemillis());
 }

 void test1() {

  connection conn = dbutil.getconnection();
  vector vs = new vector();

  try {
   statement stmt = conn.createstatement();
   for (resultset rs = stmt
     .executequery("select * from accesslog_bnas "); rs.next();) {

    vs.add(rs.getstring(1));

   }
   stmt.close();
   conn.close();
  }

  catch (sqlexception e) {
   // todo auto-generated catch block
   e.printstacktrace();
  }

 }

 void test2() {

  connection conn = dbutil.getconnection();
  vector vs = new vector();

  try {
   statement stmt = conn.createstatement();
   resultset rs = stmt.executequery("select * from accesslog_bnas ");
   while (rs.next()) {
    vs.add(rs.getstring(1));

   }

   stmt.close();
   conn.close();
  } catch (sqlexception e) {
   // todo auto-generated catch block
   e.printstacktrace();
  }

 }
}
print
1100141162919
1100141174035
1100141178942