使用Java中的循环创建变量名称？

第一次海报，长时间读者所以对我温柔:)

请参阅以下代码，该代码用于生成财务年度中每月开始和结束的时间戳。

int year = 2010; // Financial year runs from Sept-Aug so earlyMonths are those where year = FY-1 and lateMonths are those where year = FY int[] earlyMonths = {8, 9, 10, 11}; // Sept to Dec int earlyYear = year -1; for (int i : earlyMonths) { month = i; Calendar cal = Calendar.getInstance(); cal.clear(); cal.set(earlyYear,month,1,0,0,0); Long start = cal.getTimeInMillis(); cal.clear(); cal.set(earlyYear,month,1); lastDayofMonth = cal.getActualMaximum(GregorianCalendar.DAY_OF_MONTH); cal.set(earlyYear,month,lastDayofMonth,23,59,59); Long end = cal.getTimeInMillis(); } int[] lateMonths = {0, 1, 2, 3, 4, 5, 6, 7}; // Jan to Aug for (int i : lateMonths) { month = i; Calendar cal = Calendar.getInstance(); cal.clear(); cal.set(year,month,1,0,0,0); Long start = cal.getTimeInMillis(); cal.clear(); cal.set(year,month,1); lastDayofMonth = cal.getActualMaximum(GregorianCalendar.DAY_OF_MONTH); cal.set(year,month,lastDayofMonth,23,59,59); Long end = cal.getTimeInMillis(); } 

到目前为止一切都那么好，但是为了使用这些结果，我需要将这些时间戳输出到以月命名的变量（稍后在代码中用于准备好的语句中。例如SeptStart = sometimestamp，SeptEnd = some timestamp等等。

我不知道是否可以根据每个循环的结果声明新变量。 有任何想法吗？

Answer 1

为什么不使用地图 ？

毕竟你想拥有一个“容器”来获取某个值，并用指定的名称对它进行寻址。

因此，只需将“变量名称”作为您的密钥，将“变量值”作为您的值，即ehm值。

编辑，因为你想要一个Sorted集合：

首先，选择Treemap而不是Map。

另外，要保留字典顺序，请将月份数填充零标准化到左侧，并使用“开始”和“结束”作为分隔符

所以你将拥有：

 01_begin 01_end 02_begin ... 10_begin 10_end ... 

当您访问树形图时，将以正确的顺序打印。

Answer 2

不使用生成变量名称，而是使用Map ，其中键是月份名称，值是该月份的值。

而不是Date septStart = some date你可以做startDates.put("September", some date)

或者更好的是，将值存储在数组中，其中索引是月份数： startDates[8] = some date // 0-indexed!

Answer 3

您无法动态声明变量。 我建议声明两个时间戳数组（一个用于开头，一个用于结尾）并填充它们。 然后使用这些数组而不是命名变量或手动声明变量并手动设置它们。

 Calendar[] beginnings = new Calendar[12]; Calendar[] endings = new Calendar[12]; for (int i: earlyMontsh) { // Calc beginning ... beginnings[i] = cal; cal = Calendar.getInstance(); // Important, create new instance! // Calc ending ... endings[i] = cal; } // ... Same for second loop ... Calendar janStart = beginnings[0]; Calendar janEnd = endings[0]; Calendar febStart = beginnigs[1]; Calendar febEnd = endings[1]; // .. And so on ... Calendar decStart = beginnings[11]; Calendar decEnd = endings[11]; 

Answer 4

将值存储在数组中将允许您通过Calendar.Month常量访问它们

 import java.util.Calendar; import java.util.GregorianCalendar; public class Cal { Long[] start = new Long[12]; Long[] end = new Long[12]; private void init(int year) { for (int month = 0; month < 12; month++) { Calendar cal = Calendar.getInstance(); cal.clear(); cal.set(year, month, 1, 0, 0, 0); start[month] = cal.getTimeInMillis(); cal.clear(); cal.set(year, month, 1); int lastDayofMonth = cal .getActualMaximum(GregorianCalendar.DAY_OF_MONTH); cal.set(year, month, lastDayofMonth, 23, 59, 59); end[month] = cal.getTimeInMillis(); } } public static void main(String[] args) { Cal cal = new Cal(); cal.init(2010); System.out.println( "start:" + cal.start[Calendar.JANUARY]+ " - " + cal.end[Calendar.JANUARY ]); } } 

Answer 5

地图确实似乎是一个很好的解决方案:)我是java / jsp的新手（一般来说大多数编程！）所以我不知道这是多么简单:)

以下代码：

 // Financial year runs from Sept-Aug so earlyMonths are those where year = FY-1 and lateMonths are those where year = FY HashMap hm = new HashMap(); int[] earlyMonths = {8, 9, 10, 11}; // Sept to Dec int earlyYear = year -1; for (int i : earlyMonths) { month = i; Calendar cal = Calendar.getInstance(); cal.clear(); cal.set(earlyYear,month,1,0,0,0); Long start = cal.getTimeInMillis(); hm.put(month + "_start", new Long(start)); cal.clear(); cal.set(earlyYear,month,1); lastDayofMonth = cal.getActualMaximum(GregorianCalendar.DAY_OF_MONTH); cal.set(earlyYear,month,lastDayofMonth,23,59,59); Long end = cal.getTimeInMillis(); hm.put(month + "_end", new Long(end)); } int[] lateMonths = {0, 1, 2, 3, 4, 5, 6, 7}; // Jan to Aug for (int i : lateMonths) { month = i; Calendar cal = Calendar.getInstance(); cal.clear(); cal.set(year,month,1,0,0,0); Long start = cal.getTimeInMillis(); hm.put(month + "_start", new Long(start)); cal.clear(); cal.set(year,month,1); lastDayofMonth = cal.getActualMaximum(GregorianCalendar.DAY_OF_MONTH); cal.set(year,month,lastDayofMonth,23,59,59); Long end = cal.getTimeInMillis(); hm.put(month + "_end", new Long(end)); } Set set = hm.entrySet(); Iterator hmi = set.iterator(); while(hmi.hasNext()){ Map.Entry me = (Map.Entry)hmi.next(); out.println(me.getKey() + " : " + me.getValue() + "
"); } 

给我以下输出：

 4_end : 1275350399000 3_start : 1270080000000 8_end : 1254355199000 10_start : 1257033600000 1_start : 1264982400000 2_start : 1267401600000 8_start : 1251763200000 10_end : 1259625599000 0_start : 1262304000000 7_start : 1280620800000 0_end : 1264982399000 4_start : 1272672000000 5_start : 1275350400000 11_end : 1262303999000 5_end : 1277942399000 6_start : 1277942400000 9_start : 1254355200000 3_end : 1272671999000 2_end : 1270079999000 9_end : 1257033599000 11_start : 1259625600000 1_end : 1267401599000 7_end : 1283299199000 6_end : 1280620799000 

我很好奇为什么以这种方式订购？ 就function而言，它并不重要，但出于调试目的，是否可以订购hashmap？

感谢各位大家的好建议:)

Answer 6

完成后，我发布完整的代码。 它从数据库中提取有关我们的生产服务器的可用性信息，以获取管理报告。 这是我在JSP中做过的最复杂的事情:)

我相信很多事情都可以做得更优雅，所以请随意提出建议:)（显然db密码等是XXX出来的）

 <%@page language="java" contentType="text/html"%> <%@page import="java.util.*,java.sql.*,java.text.*"%>      <% // Example SQL "select count(timestamp) from jagel_hq_log where timestamp > 1270080000000 and timestamp < 1272671999000 and kpi_id = 9" /* ------------- START CONFIGURABLE VARIABLES -------------*/ int year = 2010; boolean leapYear = false; String db_user = "XXXX"; String db_pass = "XXXX"; // Special Case of Leap Years int febMins; if(leapYear=true) { febMins = 41760; } else { febMins = 44640; } int yearMins; if(leapYear=true) { yearMins = 527040; } else { yearMins = 525600; } int minsYear = yearMins; // minutes in each month int minsJan = 44640; int minsFeb = febMins; int minsMar = 44640; float minsApr = 43200; int minsMay = 44640; int minsJun = 43200; int minsJul = 44640; int minsAug = 44640; int minsSep = 43200; int minsOct = 44640; int minsNov = 43200; int minsDec = 44640; String maxAvail = "#CDEB8B"; String medAvail = "#FFFF88"; String minAvail = "#FDE8D7"; String colour; /* ------------- END CONFIGURABLE VARIABLES -------------*/ /* Initialise Variables */ int month = 0; int lastDayofMonth; int totalMins = 0; float mins_down = 0; float avail = 0; DecimalFormat round = new DecimalFormat("###.###"); Long startTime; Long endTime; // Connect to DB DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver()); String connString="jdbc:oracle:thin:@XXXXXXXX.XXXXX.com:XXXX:XXXXXX"; Connection conn = DriverManager.getConnection(connString,db_user,db_pass); /* Get months of year as 'to' and 'from' timestamps */ // Financial year runs from Sept-Aug so earlyMonths are those where 'year = FY-1' and lateMonths are those where 'year = FY' HashMap hm = new HashMap(); int[] earlyMonths = {8, 9, 10, 11}; // Sept to Dec int earlyYear = year -1; for (int i : earlyMonths) { month = i; Calendar cal = Calendar.getInstance(); cal.clear(); cal.set(earlyYear,month,1,0,0,0); Long start = cal.getTimeInMillis(); hm.put(month + "_start", new Long(start)); cal.clear(); cal.set(earlyYear,month,1); lastDayofMonth = cal.getActualMaximum(GregorianCalendar.DAY_OF_MONTH); cal.set(earlyYear,month,lastDayofMonth,23,59,59); Long end = cal.getTimeInMillis(); hm.put(month + "_end", new Long(end)); } int[] lateMonths = {0, 1, 2, 3, 4, 5, 6, 7}; // Jan to Aug for (int i : lateMonths) { month = i; Calendar cal = Calendar.getInstance(); cal.clear(); cal.set(year,month,1,0,0,0); Long start = cal.getTimeInMillis(); hm.put(month + "_start", new Long(start)); cal.clear(); cal.set(year,month,1); lastDayofMonth = cal.getActualMaximum(GregorianCalendar.DAY_OF_MONTH); cal.set(year,month,lastDayofMonth,23,59,59); Long end = cal.getTimeInMillis(); hm.put(month + "_end", new Long(end)); } %>  <-- Back to Index
 
 
IITP Availability Report
 <% Calendar c = Calendar.getInstance(); out.println("Report Generated: " + c.getTime() + " and accurate up to (and including) yesterday"); %> 
   <% // Get all KPI_ID's Statement stmt = conn.createStatement(); ResultSet rs_id = stmt.executeQuery("select distinct (KPI_ID) from JAGEL_KPI_SPECS order by KPI_ID"); // initialise Result Set ResultSet rs_minsDown; while (rs_id.next()){ int id = rs_id.getInt("KPI_ID"); // Get the kpi name and description from db PreparedStatement ps_names = conn.prepareStatement("select KPI_ID, KPI_GROUP_NAME, DESCRIPTION from JAGEL_KPI_SPECS where KPI_ID = " + id); ResultSet rs_names = ps_names.executeQuery(); while (rs_names.next()) { out.println(""); } rs_names.close(); // get the number of minutes down for each month and availability % PreparedStatement ps_minsDown = conn.prepareStatement("select count(timestamp) from jagel_hq_log where timestamp > ? and timestamp < ? and kpi_id = " + id); //September startTime = (Long) hm.get("8_start"); endTime = (Long) hm.get("8_end"); ps_minsDown.setLong(1,startTime); ps_minsDown.setLong(2,endTime); rs_minsDown = ps_minsDown.executeQuery(); rs_minsDown.next(); mins_down = rs_minsDown.getInt("COUNT(TIMESTAMP)"); avail = 100-(mins_down/minsSep*100); if(avail < 99.98) { colour=minAvail; } else if(avail < 100){ colour=medAvail; } else { colour=maxAvail; } out.println("
 
 
KPI Name
 
Description
 
Sep <% out.println( year - 1 ); %>
 
Oct <% out.println( year - 1 ); %>
 
Nov <% out.println( year - 1 ); %>
 
Dec <% out.println( year - 1 ); %>
 
Jan <% out.println( year ); %>
 
Feb <% out.println( year ); %>
 
Mar <% out.println( year ); %>
 
Apr <% out.println( year ); %>
 
May <% out.println( year ); %>
 
Jun <% out.println( year ); %>
 
Jul <% out.println( year ); %>
 
Aug <% out.println( year ); %>
 
Avg <% out.println( year ); %>
 
 
 
&nbsp
 
&nbsp
 
Mins Down
 
% Avail
 
Mins Down
 
% Avail
 
Mins Down
 
% Avail
 
Mins Down
 
% Avail
 
Mins Down
 
% Avail
 
Mins Down
 
% Avail
 
Mins Down
 
% Avail
 
Mins Down
 
% Avail
 
Mins Down
 
% Avail
 
Mins Down
 
% Avail
 
Mins Down
 
% Avail
 
Mins Down
 
% Avail
 
Mins Down
 
% Avail
 
" + rs_names.getString("KPI_GROUP_NAME") + "
" + rs_names.getString("DESCRIPTION") + "
" + mins_down + "
" + round.format(avail) + "%"); rs_minsDown.close(); //October startTime = (Long) hm.get("9_start"); endTime = (Long) hm.get("9_end"); ps_minsDown.setLong(1,startTime); ps_minsDown.setLong(2,endTime); rs_minsDown = ps_minsDown.executeQuery(); rs_minsDown.next(); mins_down = rs_minsDown.getInt("COUNT(TIMESTAMP)"); avail = 100-(mins_down/minsOct*100); if(avail < 99.98) { colour=minAvail; } else if(avail < 100){ colour=medAvail; } else { colour=maxAvail; } out.println("
" + mins_down + "
" + round.format(avail) + "%"); rs_minsDown.close(); //November startTime = (Long) hm.get("10_start"); endTime = (Long) hm.get("10_end"); ps_minsDown.setLong(1,startTime); ps_minsDown.setLong(2,endTime); rs_minsDown = ps_minsDown.executeQuery(); rs_minsDown.next(); mins_down = rs_minsDown.getInt("COUNT(TIMESTAMP)"); avail = 100-(mins_down/minsNov*100); if(avail < 99.98) { colour=minAvail; } else if(avail < 100){ colour=medAvail; } else { colour=maxAvail; } out.println("
" + mins_down + "
" + round.format(avail) + "%"); rs_minsDown.close(); //December startTime = (Long) hm.get("11_start"); endTime = (Long) hm.get("11_end"); ps_minsDown.setLong(1,startTime); ps_minsDown.setLong(2,endTime); rs_minsDown = ps_minsDown.executeQuery(); rs_minsDown.next(); mins_down = rs_minsDown.getInt("COUNT(TIMESTAMP)"); avail = 100-(mins_down/minsDec*100); if(avail < 99.98) { colour=minAvail; } else if(avail < 100){ colour=medAvail; } else { colour=maxAvail; } out.println("
" + mins_down + "
" + round.format(avail) + "%"); rs_minsDown.close(); //January startTime = (Long) hm.get("0_start"); endTime = (Long) hm.get("0_end"); ps_minsDown.setLong(1,startTime); ps_minsDown.setLong(2,endTime); rs_minsDown = ps_minsDown.executeQuery(); rs_minsDown.next(); mins_down = rs_minsDown.getInt("COUNT(TIMESTAMP)"); avail = 100-(mins_down/minsJan*100); if(avail < 99.98) { colour=minAvail; } else if(avail < 100){ colour=medAvail; } else { colour=maxAvail; } out.println("
" + mins_down + "
" + round.format(avail) + "%"); rs_minsDown.close(); //February startTime = (Long) hm.get("1_start"); endTime = (Long) hm.get("1_end"); ps_minsDown.setLong(1,startTime); ps_minsDown.setLong(2,endTime); rs_minsDown = ps_minsDown.executeQuery(); rs_minsDown.next(); mins_down = rs_minsDown.getInt("COUNT(TIMESTAMP)"); avail = 100-(mins_down/minsFeb*100); if(avail < 99.98) { colour=minAvail; } else if(avail < 100){ colour=medAvail; } else { colour=maxAvail; } out.println("
" + mins_down + "
" + round.format(avail) + "%"); rs_minsDown.close(); //March startTime = (Long) hm.get("2_start"); endTime = (Long) hm.get("2_end"); ps_minsDown.setLong(1,startTime); ps_minsDown.setLong(2,endTime); rs_minsDown = ps_minsDown.executeQuery(); rs_minsDown.next(); mins_down = rs_minsDown.getInt("COUNT(TIMESTAMP)"); avail = 100-(mins_down/minsMar*100); if(avail < 99.98) { colour=minAvail; } else if(avail < 100){ colour=medAvail; } else { colour=maxAvail; } out.println("
" + mins_down + "
" + round.format(avail) + "%"); rs_minsDown.close(); //April startTime = (Long) hm.get("3_start"); endTime = (Long) hm.get("3_end"); ps_minsDown.setLong(1,startTime); ps_minsDown.setLong(2,endTime); rs_minsDown = ps_minsDown.executeQuery(); rs_minsDown.next(); mins_down = rs_minsDown.getInt("COUNT(TIMESTAMP)"); avail = 100-(mins_down/minsApr*100); if(avail < 99.98) { colour=minAvail; } else if(avail < 100){ colour=medAvail; } else { colour=maxAvail; } out.println("
" + mins_down + "
" + round.format(avail) + "%"); rs_minsDown.close(); //May startTime = (Long) hm.get("4_start"); endTime = (Long) hm.get("4_end"); ps_minsDown.setLong(1,startTime); ps_minsDown.setLong(2,endTime); rs_minsDown = ps_minsDown.executeQuery(); rs_minsDown.next(); mins_down = rs_minsDown.getInt("COUNT(TIMESTAMP)"); avail = 100-(mins_down/minsMay*100); if(avail < 99.98) { colour=minAvail; } else if(avail < 100){ colour=medAvail; } else { colour=maxAvail; } out.println("
" + mins_down + "
" + round.format(avail) + "%"); rs_minsDown.close(); //June startTime = (Long) hm.get("5_start"); endTime = (Long) hm.get("5_end"); ps_minsDown.setLong(1,startTime); ps_minsDown.setLong(2,endTime); rs_minsDown = ps_minsDown.executeQuery(); rs_minsDown.next(); mins_down = rs_minsDown.getInt("COUNT(TIMESTAMP)"); avail = 100-(mins_down/minsMay*100); if(avail < 99.98) { colour=minAvail; } else if(avail < 100){ colour=medAvail; } else { colour=maxAvail; } out.println("
" + mins_down + "
" + round.format(avail) + "%"); rs_minsDown.close(); //July startTime = (Long) hm.get("6_start"); endTime = (Long) hm.get("6_end"); ps_minsDown.setLong(1,startTime); ps_minsDown.setLong(2,endTime); rs_minsDown = ps_minsDown.executeQuery(); rs_minsDown.next(); mins_down = rs_minsDown.getInt("COUNT(TIMESTAMP)"); avail = 100-(mins_down/minsJul*100); if(avail < 99.98) { colour=minAvail; } else if(avail < 100){ colour=medAvail; } else { colour=maxAvail; } out.println("
" + mins_down + "
" + round.format(avail) + "%"); rs_minsDown.close(); //August startTime = (Long) hm.get("7_start"); endTime = (Long) hm.get("7_end"); ps_minsDown.setLong(1,startTime); ps_minsDown.setLong(2,endTime); rs_minsDown = ps_minsDown.executeQuery(); rs_minsDown.next(); mins_down = rs_minsDown.getInt("COUNT(TIMESTAMP)"); avail = 100-(mins_down/minsAug*100); if(avail < 99.98) { colour=minAvail; } else if(avail < 100){ colour=medAvail; } else { colour=maxAvail; } out.println("
" + mins_down + "
" + round.format(avail) + "%"); rs_minsDown.close(); //YEAR startTime = (Long) hm.get("8_start"); endTime = (Long) hm.get("7_end"); ps_minsDown.setLong(1,startTime); ps_minsDown.setLong(2,endTime); rs_minsDown = ps_minsDown.executeQuery(); rs_minsDown.next(); mins_down = rs_minsDown.getInt("COUNT(TIMESTAMP)"); avail = 100-(mins_down/minsYear*100); if(avail < 99.98) { colour=minAvail; } else if(avail < 100){ colour=medAvail; } else { colour=maxAvail; } out.println("
" + mins_down + "
" + round.format(avail) + "%"); rs_minsDown.close(); } // close remaining result set and connection rs_id.close(); conn.close(); %> 
  
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