java - 在Java中使用循环创建变量名？

Question

第一次发帖，老读者，所以对我温柔:)

请参阅以下代码，它可以为我生成一个财政年度每个月的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();
}

到目前为止一切都很好，但为了使用这些结果，我需要将这些时间戳输出到按月份命名的变量（在代码后面的准备好的语句中使用。例如，SeptStart = 有时，SeptEnd = 一些时间戳等等等。

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？

score 9 · Accepted Answer

为什么不使用地图？

毕竟，您希望为某个值拥有一个“容器”并使用指定的名称对其进行寻址。

因此，只需将“变量名”设为您的键，将“变量值”设为您的，嗯，值。

编辑是因为您想要一个 Sorted 集合：

首先，使用Treemap而不是 Map。

此外，为了保留词典顺序，将您的月份编号标准化为左侧填充零，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，它将以正确的顺序打印。

score 4 · Accepted Answer

使用 a 代替生成变量名称，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，将值存储在一个数组中，其中索引是月份数：startDates[8] = some date // 0-indexed!

score 2 · Accepted Answer

您不能动态声明变量。我建议声明两个时间戳数组（一个用于开始，一个用于结束）并填充它们。然后要么使用这些数组而不是命名变量，要么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];

score 2 · Accepted Answer

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 ]);
    }

}

score 0 · Accepted Answer

地图确实似乎是一个很好的解决方案 :) 我是 java / jsp 的新手（通常是大多数编程！）所以我不知道这有多简单 :)

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() + "<br>");
}

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它？就功能而言，这并不重要，但出于调试目的，是否可以订购 hashmap？

感谢大家的好建议：）

score 0 · Accepted Answer

为了完成，我发布了完整的代码。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生成管理报告。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，所以请随时提出建议:)（显然 db 密码等已被 XXX 删除）

<%@page language="java" contentType="text/html"%>
<%@page import="java.util.*,java.sql.*,java.text.*"%>
<html>
<head>
    <title>KPI: FY10</title>
    <link rel="stylesheet" type="text/css" href="reports.css">
</head>
<%
// 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));
}
%>

<!-- Header -->
<a href="index.jsp"><-- Back to Index</a><br>
<div align="center">
<h2>IITP Availability Report</h2>
<%
Calendar c = Calendar.getInstance();
out.println("Report Generated: " + c.getTime() + " and accurate up to (and including) yesterday");
%>
</div>

<!-- Start Table -->
<table class="mar">
<tr>
    <th class="header">KPI Name</th>
    <th class="header">Description</th>
    <th class="header" colspan="2">Sep <% out.println( year - 1 ); %></th>  
    <th class="header" colspan="2">Oct <% out.println( year - 1 ); %></th>  
    <th class="header" colspan="2">Nov <% out.println( year - 1 ); %></th>
    <th class="header" colspan="2">Dec <% out.println( year - 1 ); %></th>
    <th class="header" colspan="2">Jan <% out.println( year ); %></th>
    <th class="header" colspan="2">Feb <% out.println( year ); %></th>
    <th class="header" colspan="2">Mar <% out.println( year ); %></th>
    <th class="header" colspan="2">Apr <% out.println( year ); %></th>
    <th class="header" colspan="2">May <% out.println( year ); %></th>
    <th class="header" colspan="2">Jun <% out.println( year ); %></th>
    <th class="header" colspan="2">Jul <% out.println( year ); %></th>
    <th class="header" colspan="2">Aug <% out.println( year ); %></th>
    <th class="header" colspan="2">Avg <% out.println( year ); %></th>
</tr>
<tr>
    <th class="top">&nbsp</th>
    <th class="top">&nbsp</th>
    <th class="top">Mins Down</th>
    <th class="top">% Avail</th>
    <th class="top">Mins Down</th>
    <th class="top">% Avail</th>
    <th class="top">Mins Down</th>
    <th class="top">% Avail</th>
    <th class="top">Mins Down</th>
    <th class="top">% Avail</th>
    <th class="top">Mins Down</th>
    <th class="top">% Avail</th>
    <th class="top">Mins Down</th>
    <th class="top">% Avail</th>
    <th class="top">Mins Down</th>
    <th class="top">% Avail</th>
    <th class="top">Mins Down</th>
    <th class="top">% Avail</th>
    <th class="top">Mins Down</th>
    <th class="top">% Avail</th>
    <th class="top">Mins Down</th>
    <th class="top">% Avail</th>
    <th class="top">Mins Down</th>
    <th class="top">% Avail</th>
    <th class="top">Mins Down</th>
    <th class="top">% Avail</th>
    <th class="top">Mins Down</th>
    <th class="top">% Avail</th>
</tr>
<%
// 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("<tr><td>" + rs_names.getString("KPI_GROUP_NAME") + "</td><td>" + rs_names.getString("DESCRIPTION") + "</td>");
    }
    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("<td bgcolor=" + colour + ">" + mins_down + "</td><td bgcolor=" + colour + ">" + 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("<td bgcolor=" + colour + ">" + mins_down + "</td><td bgcolor=" + colour + ">" + 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("<td bgcolor=" + colour + ">" + mins_down + "</td><td bgcolor=" + colour + ">" + 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("<td bgcolor=" + colour + ">" + mins_down + "</td><td bgcolor=" + colour + ">" + 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("<td bgcolor=" + colour + ">" + mins_down + "</td><td bgcolor=" + colour + ">" + 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("<td bgcolor=" + colour + ">" + mins_down + "</td><td bgcolor=" + colour + ">" + 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("<td bgcolor=" + colour + ">" + mins_down + "</td><td bgcolor=" + colour + ">" + 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("<td bgcolor=" + colour + ">" + mins_down + "</td><td bgcolor=" + colour + ">" + 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("<td bgcolor=" + colour + ">" + mins_down + "</td><td bgcolor=" + colour + ">" + 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("<td bgcolor=" + colour + ">" + mins_down + "</td><td bgcolor=" + colour + ">" + 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("<td bgcolor=" + colour + ">" + mins_down + "</td><td bgcolor=" + colour + ">" + 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("<td bgcolor=" + colour + ">" + mins_down + "</td><td bgcolor=" + colour + ">" + 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("<td bgcolor=" + colour + ">" + mins_down + "</td><td bgcolor=" + colour + ">" + round.format(avail) + "%");
    rs_minsDown.close();
}
// close remaining result set and connection
rs_id.close();
conn.close();
%>
</table>
<!-- Footer -->
<br><a href="index.jsp"><-- Back to Index</a>
</body>
</html>

java - 在Java中使用循环创建变量名？

6 回答 6

Related

Reference