小编Jor*_*pos的帖子

我是Java的新手,我现在正在尝试不同的东西......主要是创建简单的计算器,只是为了练习使用这种语言.我的问题是,如何将响应中的小数位数限制为仅2或3个小数位,而不是我现在得到的数字.这是我为毕达哥拉斯计算器编写的代码......

基本上,我希望"回答"返回一个只有几个小数位的数字,我无法弄清楚如何做到这一点.

谢谢!

public class PythagoreanTheorem {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double numOne, numTwo, aSquared, bSquared, cSquared, answer;

        System.out.println("Enter the value for Side-A: ");
        numOne = sc.nextDouble();

        System.out.println("Enter the value for Side-B: ");
        numTwo = sc.nextDouble();

        aSquared = numOne * numOne;
        bSquared = numTwo * numTwo;
        cSquared = aSquared + bSquared;

        answer = Math.sqrt(cSquared);

        System.out.println("Side-C is: " + answer);
    }
}

我正在尝试制作一个正则表达式,它将匹配一个帐号,该帐号由特定的3个字符串后跟9个数字组成.例如

abc123456789
xyz123456789
def987654321

我已经想出如何用下面的表达式来完成,但想知道是否有更好的方法:

abc[0-9]{9}|xyz[0-9]{9}|def[0-9]{9}

我有一个非常奇怪的问题.我正在查询数据并将其格式化为json.格式工作得很好,但是当我尝试添加一个案例来防止,出现在json的最后一项时,我的SQL语句的"按日期排序"不起作用,我只是通过ID命令它.有什么想法？

$sql = "SELECT * FROM events ORDER BY date";
$res = mysql_query($sql,$con);
$number = mysql_num_rows($res);
$json = 'var event_data={';
$i = 1;
while ($row = mysql_fetch_assoc($res))
    {
    $json .= '"'.$row['id'].'": {';
    $json .= '"loc_id":"'.$row['loc_id'].'"';
    $json .= ', "type":"'.$row['type'].'"';
    $json .= ', "time":"'.$row['time'].'"';
    $json .= ', "date":"'.$row['date'].'"}';
    if ($i < $number)
       {
           $json .= ',';  //<----- this is the problem child
       }else{
           $json .= '';
       }
     $i ++;
    }
$json .= '};';  
echo $json;

我有以下返回数据的 SELECT 语句，示例如下：

SELECT performers.ID, 
       performers.Name, 
       COUNT(*) AS CountOfDeals, 
       COUNT(DISTINCT(deals.Name)) AS CountOfAliases 
  FROM deals RIGHT JOIN performers 
               ON deals.name LIKE CONCAT('%', performers.name, '%') 
 WHERE performers.ID IN ( 27952, 27951, 27950, 27949, 27948 ) 
 GROUP BY Name;

返回的数据示例：

  ID        Name             CountOfDeals     CountOfAliases
27952   Christine Hoberg          1                 0
27951   Indian Jewelry            1                 0
27952   Kinky Friedman            5                 3
27949   KJ-52                     1                 0
27960   River Whyless             1                 0

我想将其与以下 UPDATE 语句结合起来

UPDATE performers 
   SET RawAliasCount = CountOfAliases, 
       RawDealCount = CountOfDeals 
 WHERE ID = …

我有 2 张桌子：

interests (storing the interest ID and name)
person_interests(storing the person_id and interest_id)

如何选择特定人未选择的所有兴趣？

我已经尝试了以下 SQL 查询，但仍然没有得到想要的结果

SELECT * 
  FROM interests LEFT JOIN person_interests 
               ON interests.id=person_interests.person_id
 WHERE person_interests.id IS NULL 
   AND person_id=66;

所以我有这两个类叫做装运和保险,一个计算运费的价格,另一个加上保险.出货逻辑工作正常,但由于某种原因保险类中的if语句不起作用,我不知道发生了什么.保险费用的输出总是2.45.它为什么这样做？

装运等级:

  package theshipment;

  public class Shipment extends Main {
      protected double weight = Double.parseDouble(savedArgs[1]);
      protected double shippingCost;
      protected double methodCost;
      protected String method = savedArgs[2];

      public void calculateShippingCost(){

        if (weight<=10||weight>=1){
            if (method.equalsIgnoreCase("T"))
                methodCost = weight * 3.00;
            else if (method.equalsIgnoreCase("A"))
                methodCost = weight * 4.00;
            else if (method.equalsIgnoreCase("M"))
                methodCost = weight * 2.00;
            else{}
        }else if (weight<=20||weight>=10.1){
            if (method.equalsIgnoreCase("T"))
                methodCost = weight * 2.45;
            else if (method.equalsIgnoreCase("A"))
                methodCost = weight * 3.00;
            else if (method.equalsIgnoreCase("M"))
                methodCost = weight * …

查看以下 3 个 MySQL 表的索引长度是否通常比实际行数高得多？

在开始快速降低性能之前，索引的长度是否有限制，例如第一个索引长度为 2.06 亿以上的表？

table_rows  data_length index_length    Size in MB
7607749     5044389164  206542848       5007.68
3110749     1832710212  793864192       2504.9
4811507     1088374128  318001152       1341.22

当我执行：

  @SqlQuery("select A.field1, A.field2, C.field3, C.field4, C.field5 from "
  + "table1 A, table2 B, table3 C WHERE A.field2 >= '1500' AND A.field2 < '9500' "
  + "AND A.field1 NOT IN (SELECT field1 FROM table4) AND A.field1 = B.field1  AND "
  + "(B.field3 = 'NAME' OR B.field3 ='STRT') order by A.field1 ASC") 

我不断收到以下错误：

problem parsing template 'c2VsZWN0IEEuVVBDX05VTSwgQS5NT0RVTEVfTlVNLCBDLkNIUl9OTSwgQy5DSFJfQ0QsIEMuVkwgZnJvbSBVUEMgQSwgVVBDX0NIUiBCLCBDSFJfVkwgQyBXSEVSRSBBLk1PRFVMRV9OVU0gPj0gJzEwMDAnIEFORCBBLk1PRFVMRV9OVU0gPCAnOTAwMCcgQU5EIEEuVVBDX05VTSBOT1QgSU4gKFNFTEVDVCBVUENfTlVNIEZST00gVVBDX0FDVFYpIEFORCBBLlVQQ19OVU0gPSBCLlVQQ19OVU0gIEFORCAoQi5DSFJfTk0gPSAnQlJBTkQnIE9SIEIuQ0hSX05NID0nVFlQRScpIEFORCBCLk1PRFVMRV9OVU0gPSBDLk1PRFVMRV9OVU0gIEFORCBCLkNIUl9OTSA9IEMuQ0hSX05NICBBTkQgQi5DSFJfQ0QgPSBDLkNIUl9DRCBvcmRlciBieSBBLlVQQ19OVU0gQVND'
line 1:373: expecting '>', found '<EOF>'
at org.antlr.stringtemplate.language.AngleBracketTemplateLexer.nextToken(AngleBracketTemplateLexer.java:149)
at antlr.TokenBuffer.fill(TokenBuffer.java:69)
at antlr.TokenBuffer.LA(TokenBuffer.java:80)
at antlr.LLkParser.LA(LLkParser.java:52)
at org.antlr.stringtemplate.language.TemplateParser.template(TemplateParser.java:103)
at org.antlr.stringtemplate.StringTemplate.breakTemplateIntoChunks(StringTemplate.java:850)
at org.antlr.stringtemplate.StringTemplate.setTemplate(StringTemplate.java:441)
at org.antlr.stringtemplate.StringTemplateGroup.defineTemplate(StringTemplateGroup.java:679)
at org.skife.jdbi.v2.sqlobject.stringtemplate.StringTemplate3StatementLocator.locate(StringTemplate3StatementLocator.java:260) …