Java未入门

Microsoft JDBC "ResultSet Can Not Re-Read Row Data" Error

spacer — 2005-12-09 10:26:00Z

A：使用MS SQL Server 2000 SP3a/SP4做数据库服务器时，用Microsoft提供的JDBC驱动(2.2.0040)，在查询时遇到一个SQLException：
java.sql.SQLException: [Microsoft][SQLServer 2000 Driver for JDBC]ResultSet can not re-read row data for column #。查询语句和JDBC代码都没有问题，怀疑是Microsoft驱动的BUG，google一下果然在Microsoft support站点发现了问题：http://support.microsoft.com/kb/824106，原因是如果该表存在TEXT, NTEXT, IMAGE等大型字段，对于ResultSet的字段读取必须按照从左向右读，如果你用：
int a = rs.getInt(2);
int b = rs.getInt(1);
则报错。Microsoft给出的方案是不能从右往左也不能连续读2次。没办法自己改代码，严格从左向右读，结果就没有问题了。

Jbuilder2006安装后第二次启动失败

飞天 — 2005-11-04 20:04:00Z

　正常安装，然后运行，一切正常

　关闭
　再启动
　只出现了启动画面
　然后就什么也没有了。

　用Google一搜　jbuilder2006 启动　得到如下提示：

　　start > run > cmd.exe > cd <jb2006>\bin > jbuilder.exe　or JBuilder.exe -verbose　看exception

　然后编辑/bin下的jbuilder.config文件，原来　　vmmemmax设置的值为75%,我将其改为128m就可以了，如果你的内存空间够大，还可以再设置大些，比如256m

　相关文章：　http://www.cjsdn.net/post/view?bid=7&id=159125

　我的机器内存是1.5G，可能出在这儿了：

　我修改jbuilder.config：

vmmemmin 128m
vmmemmax 512m
vmparam -XX:MaxPermSize=512m

今天编译java的遇到的问题

飞天 — 2005-04-13 16:12:00Z

1 在引用 import java.util.regex 时没有注意 regex是一包
    正确应是 import java.util.regex.*
    出错: regex.java:1: cannot find symbol
          symbol : class regex
          location: package java.util

2 机器上有两个不同的java环境，编译javac 和运行 java，由于
    没有指定目录在运行时出错

    出错：Exception in thread "main" java.lang.UnsupportedClassVersionError: Regex (Unsupp
          orted major.minor version 49.0)

3 main函数没有加参数而声明

    public static void main()
    {
    }

    编译过通过，但运行出错

    出错：Exception in thread "main" java.lang.NoSuchMethodError: main

    正确
    public static void main(String[] args)
    {
    }

4 在当前目录加java环境变量
    set CLASSPATH=.;D:\Java\jdk1.5.0\lib;D:\Java\jdk1.5.0\lib\tools.jar

想好好学java吧, 做下一个吃饭的东东

java 批处理运行

飞天 — 2005-03-14 23:41:00Z

@echo off
set CP=D:\Java\JRun4\lib\jrun.jar;%CLASSPATH%
set cmd=java -classpath "%CP%" %*
echo %cmd%
%cmd%
set CP=

昨天，去听李维的课，关于JBuildX的ALM

飞天 — 2004-09-02 08:59:00Z

李维把JBuildX的ALM(软件应用周期解决方案)

http://www.borland.com.cn/events/Java_Seminar2004_Reg.html

一个 The Formatter Class in J2SE 1.5 例子

飞天 — 2004-06-02 13:38:00Z

/*
* Created on 2004-6-1
*
* To change the template for this generated file go to
* Window>Preferences>Java>Code Generation>Code and Comments
*/
/**
* @author pal
*
* To change the template for this generated type comment go to
* Window>Preferences>Java>Code Generation>Code and Comments
*/

/**
*
* 在Delphi中用习惯 Format() 函数, 好在 Java 1.5.0 中支持了:)
*
*
*/

import java.util.*;

public class TestFormatter
{
public static void main(String[] args)
{
  String str1 = "aa";
  String str2 = "eeee";
  Integer a = new Integer(65);

  // Char
  Object[] objs = new Object[1];
  objs[0] = a;
  // %n 回车换行
  System.out.printf("char: %c %n", objs);

  // Integer
  Object[] objs1 = new Object[5];
  objs1[0] = a;
  objs1[1] = a;
  objs1[2] = a;
  objs1[3] = a;
  String str = String.format("char: %c integral: %d octal: %o hex: %x %n", objs1);
    System.out.println(str);

    // String
    Object[] objs2 = new Object[3];
    objs2[0] = new String("syd");
    objs2[1] = new String("fly");
  System.out.printf("reason: %s (noted by %s) %n", objs2);

  // Date
  Object[] objs3 = new Object[1];
  objs3[0] = new Date();
  //文档中的 tL 好像没有实现, 可以参考jdk厡代码
  System.out.printf("%1$tY-%1$tm-%1$td %1$tH:%1$tM:%1$tS %1$tN %n", objs3);
  System.out.printf("%1$tF %1$tT %n", objs3);

  // Float
  Object[] objs4 = new Object[1];
  objs4[0] = new Float(6.0);
  StringBuffer buff = new StringBuffer();
  Formatter ft = new Formatter(buff);
  ft.format("a float numberic: %f %n", objs4);
  System.out.println(buff.toString());
}
}

The Formatter Class in J2SE 1.5

飞天 — 2004-06-01 10:27:00Z

文章来源: http://www.developer.com/java/other/article.php/3327721

The Formatter Class in J2SE 1.5
By Jeff Langr

Java 1.5 introduces a new class named java.util.Formatter that allows you to do string formatting similar to the printf function in C. It depends heavily on the varargs feature being introduced in 1.5.

System.out.printf

The first way you'll learn to work with the Formatter is not to interact with it directly, but instead to use the new PrintStream method printf. You're probably most familiar with PrintStream from doing System.out.println calls. Here is a simple example of the new printf method:

String initials = "jjl";
String comment  = "just because";
System.out.printf("reason: %s (noted by %s)", comment, initials);

The example prints the following output on the console:

reason: just because (noted by jjl)

In the example code, you are passing printf a format string that contains embedded format specifiers. You also pass it a list of arguments, each of which corresponds to a format specifier. There are two format specifiers in the example: %s and %s. The first corresponds to the comment argument, and the second corresponds to the initials argument.

A % in a format string designates the start of a format specifier. The end of a format specifier is triggered by one of many possible characters known as conversions. In the %s format specifier, the lowercase s indicates a String conversion. A string conversion means that Java calls toString on the corresponding argument, and substitutes the result for the format specifier.

String.format

If you only want to obtain a formatted string, but not print it, you can use the static method format on the String class. Here's an example that also demonstrates a few numeric conversions:

int a = 65;
String s = 
   String.format("char: %c integral: %d octal: %o hex: %x %n",
      a, a, a, a);

The %n at the end of the format string indicates a platform-specific line separator. When printed, the String s looks like this:

char: A integral: 65 octal: 101 hex: 41

Numeric conversions also support flags for padding, grouping, justification, and sign.

Note: There are four arguments, each using the reference a. Were you to supply only three, or were one of the arguments an invalid type (for example, a string), the format method would have generated one of a few runtime exceptions. This is unlike C, which ignores any formatting problems.

If you want to use the same argument more than once against a format string, you can use a shortcut:

String s = String.format("char: %c integral:
           %<d octal: %<o hex: %<x %n", a);

The a reference is specified only once. The less-than sign (<) in a format specifier means that it should use the same argument as the last format specifier.

Dates

Formatter provides an extensive number of date-related conversions. The following code:

String.format("%1$td %1$tb %1$ty", new Date())

produces a string with the value:

26 Feb 04

The 1$ in each format specifier is another way to designate which argument to use. In this example, all three format specifiers target the first argument.

The last part of each format specifier is how you do date conversions—using a two-character sequence starting with a t. The second character indicates the date part to convert. For example, td in the first specifier converts the day of the month.

java.util.Formatter

The Formatter class is at the core of the new formatting capability. It fully supports internationalization by letting you pass a Locale to the constructor; the other formatting methods (e.g. String.format) also allow this.

Formatter also lets you pass an Appendable object. This is a new interface that defines append methods so that the formatter can store its results in a text collector such as a stream object. Sun has modified all relevant Java classes, such as StringBuffer and PrintStream, to implement this interface. Here's how you might use it:

double avogadro     = 6.0e23;
StringBuffer buffer = new StringBuffer();
Formatter formatter = new Formatter(buffer, Locale.US);
formatter.format("avogadro's number: %e %n", avogadro);
formatter.format("base of the natural log: %e %n", Math.E);
System.out.println(buffer.toString());

The corresponding output:

avogadro's number:       6.000000e+23
base of the natural log: 2.718282e+00

Summary

There are dozens of conversions available in the Formatter class and a few more things that are not covered here. To learn more about formatting, refer to the Java API documentation pages for java.util.Formatter.

Trying It Out

You can download the current beta version of J2SE 1.5 from Sun's Web site.

About the Author

Jeff Langr is a freelance author and the owner of Langr Software Solutions. He is working on a second book on Java and test-driven development entitled Agile Java, due out from Prentice Hall in fall 2004.