java 一个类中可以嵌套多少次类？
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原文地址: http://stackoverflow.com/questions/1785686/
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How many times can classes be nested within a class?
提问by Kushal Paudyal
I came across this questions on one of the online Java Tests. The options were 4,5,8 and any number of times.
我在其中一个在线 Java 测试中遇到了这个问题。选项是 4、5、8 和任意次数。
I have only used one inner class, but have never tried multiple ones. I was wondering if anyone knows the answer.
我只使用了一个内部类，但从未尝试过多个内部类。我想知道是否有人知道答案。
采纳答案by Kushal Paudyal
I tried on my own: The answer is any number of times. The following is my test class, I had no compilation errors.
我自己尝试过：答案是任意次数。以下是我的测试类，我没有编译错误。
public class Test {
public Test ()
{
}
public static void main (String args[])
{
new Test ();
}
class Test2
{
class Test3
{
class Test4
{
class Test5{
class Test6{
class Test7{
class Test8{
class Test9
{
}
}
}
}
}
}
}
}
}
回答by Mark Byers
It's a completely irrelevant question and I hope they weren't using the results for anything important. I guess the answer they were looking for was 'any number of times' but in practice there will be a limit in any given implementation of Java. If it's not defined directly it will be determined by something like the maximum file size, or some other (possibly undocumented) internal limit. The best way to find out is to try it.
这是一个完全不相关的问题，我希望他们没有将结果用于任何重要的事情。我猜他们正在寻找的答案是“任意次数”，但在实践中，任何给定的 Java 实现都会受到限制。如果它没有直接定义，它将由最大文件大小或其他一些（可能未记录的）内部限制决定。找出答案的最好方法是尝试。
Update: 30 works, but 300 gives this error:
更新： 30 有效，但 300 给出了这个错误：
A.java:3: error while writing B0.B1.B2.B3.B4.B5.B6.B7.B8.B9.B10.B11.B12.B13.B14.
B15.B16.B17.B18.B19.B20.B21.B22.B23.B24.B25.B26.B27.B28.B29.B30.B31.B32.B33.B34.
B35.B36.B37.B38.B39.B40.B41.B42.B43.B44.B45.B46.B47.B48.B49.B50.B51.B52.B53.B54.
B55.B56.B57.B58.B59.B60.B61.B62.B63.B64.B65.B66.B67.B68.B69.B70.B71.B72.B73.B74.
B75.B76.B77.B78.B79.B80.B81.B82.B83.B84.B85.B86.B87.B88.B89.B90.B91.B92.B93.B94.
B95.B96.B97.B98.B99.B100.B101.B102.B103.B104.B105.B106.B107.B108.B109.B110.B111.
B112.B113.B114.B115.B116.B117.B118.B119.B120.B121.B122.B123.B124.B125.B126.B127.
B128.B129.B130.B131.B132.B133.B134.B135.B136.B137.B138.B139.B140.B141.B142.B143.
B144.B145.B146.B147.B148.B149.B150.B151.B152.B153.B154.B155.B156.B157.B158.B159.
B160.B161.B162.B163.B164.B165.B166.B167.B168.B169.B170.B171.B172.B173.B174.B175.
B176.B177.B178.B179.B180.B181.B182.B183.B184.B185.B186.B187.B188.B189.B190.B191.
B192.B193.B194.B195.B196.B197.B198.B199.B200.B201.B202.B203.B204.B205.B206.B207.
B208.B209.B210.B211.B212.B213.B214.B215.B216.B217.B218.B219.B220.B221.B222.B223.
B224.B225.B226.B227.B228.B229.B230.B231.B232.B233.B234.B235.B236.B237.B238.B239.
B240.B241.B242.B243.B244.B245.B246.B247.B248.B249.B250.B251.B252.B253.B254.B255.
B256.B257.B258.B259.B260.B261.B262.B263.B264.B265.B266.B267.B268.B269.B270.B271.
B272.B273.B274.B275.B276.B277.B278.B279.B280.B281.B282.B283.B284.B285.B286.B287.
B288.B289.B290.B291.B292.B293.B294.B295.B296.B297.B298.B299: B0$B1$B2$B3$B4$B5$B
6$B7$B8$B9$B10$B11$B12$B13$B14$B15$B16$B17$B18$B19$B20$B21$B22$B23$B24$B25$B26$B
27$B28$B29$B30$B31$B32$B33$B34$B35$B36$B37$B38$B39$B40$B41$B42$B43$B44$B45$B46$B
47$B48$B49$B50$B51$B52$B53$B54$B55$B56$B57$B58$B59$B60$B61$B62$B63$B64$B65$B66$B
67$B68$B69$B70$B71$B72$B73$B74$B75$B76$B77$B78$B79$B80$B81$B82$B83$B84$B85$B86$B
87$B88$B89$B90$B91$B92$B93$B94$B95$B96$B97$B98$B99$B100$B101$B102$B103$B104$B105
$B106$B107$B108$B109$B110$B111$B112$B113$B114$B115$B116$B117$B118$B119$B120$B121
$B122$B123$B124$B125$B126$B127$B128$B129$B130$B131$B132$B133$B134$B135$B136$B137
$B138$B139$B140$B141$B142$B143$B144$B145$B146$B147$B148$B149$B150$B151$B152$B153
$B154$B155$B156$B157$B158$B159$B160$B161$B162$B163$B164$B165$B166$B167$B168$B169
$B170$B171$B172$B173$B174$B175$B176$B177$B178$B179$B180$B181$B182$B183$B184$B185
$B186$B187$B188$B189$B190$B191$B192$B193$B194$B195$B196$B197$B198$B199$B200$B201
$B202$B203$B204$B205$B206$B207$B208$B209$B210$B211$B212$B213$B214$B215$B216$B217
$B218$B219$B220$B221$B222$B223$B224$B225$B226$B227$B228$B229$B230$B231$B232$B233
$B234$B235$B236$B237$B238$B239$B240$B241$B242$B243$B244$B245$B246$B247$B248$B249
$B250$B251$B252$B253$B254$B255$B256$B257$B258$B259$B260$B261$B262$B263$B264$B265
$B266$B267$B268$B269$B270$B271$B272$B273$B274$B275$B276$B277$B278$B279$B280$B281
$B282$B283$B284$B285$B286$B287$B288$B289$B290$B291$B292$B293$B294$B295$B296$B297
$B298$B299.class (The filename, directory name, or volume label syntax is incorr
ect)
Code used to generate source (written in Python):
用于生成源代码（用 Python 编写）：
n = input()
print "class A{public static void main(String[] a){}}\n"
print ''.join("class B%d{" % x for x in range(n)) + '}' * n
Disappointing. I was actually hoping it would be a lot more. I wonder if it could get much further on another system which allows longer filenames.
令人失望。我实际上希望它会更多。我想知道它是否可以在另一个允许更长文件名的系统上走得更远。
回答by Greg D
Hmmm. I know that the online Java test you refer to is a lousy one. Does that count?
嗯。我知道您提到的在线 Java 测试很糟糕。算不算？
(This is the kind of limit that is irrelevant in practical experience. A similarly ridiculously question would be, "What is the maximum length of a function in bytes?")
（这是一种与实际经验无关的限制。一个同样可笑的问题是，“函数的最大长度是多少字节？”）
回答by Jim Ferrans
The true answer is none of the above. Javac will of course allow arbitrary nesting, but the underlying file system and/or OS have restrictions. We found recently that during startup the JVM running a Glassfish Java EE application server instance will hold open files to each .class during loading/JIT compilation. If you're running CentOS Linux say, the default limit on open files/process is 1024, so if you have a lot of classes being loaded at once and don't set the ulimit -nto a higher value, the JVM will hit "too many open files". And @Mark Byers' example shows that the .class file names get very long and can hit the file system name length limit, if there is one.
真正的答案不是以上任何一个。Javac 当然允许任意嵌套，但底层文件系统和/或操作系统有限制。我们最近发现，在启动期间，运行 Glassfish Java EE 应用程序服务器实例的 JVM 将在加载/JIT 编译期间将打开的文件保存到每个 .class。如果您正在运行 CentOS Linux，例如，打开文件/进程的默认限制是 1024，因此如果您一次加载了很多类并且没有将其ulimit -n设置为更高的值，JVM 将遇到“太多”打开文件”。@Mark Byers 的示例表明 .class 文件名变得很长并且可能达到文件系统名称长度限制（如果有的话）。
回答by rsp
As a follow-up to Mark's trial on windows - a bit silly but fun nonetheless - I did a trial on AIX 5.3.
作为 Mark 在 windows 上试用的后续行动（虽然有点傻但很有趣），我在 AIX 5.3 上进行了试用。
91 subclasses deep is ok, number 92 results in the following error:
深 91 个子类没问题，编号 92 导致以下错误：
-rw-r--r-- 1 root system 12813 Nov 24 15:15 A.class
Main class=class A
count=90 class=A$B$C$D$E$F$G$H$I$J$K$L$M$N$O$P$Q$R$S$T$U$V$W$X$Y$Z$AA$AB$AC$AD$AE$AF$AG$AH$AI$AJ$AK$AL$AM$AN$AO$AP$AQ$AR$AS$AT$AU$AV$AW$AX$AY$AZ$BA$BB$BC$BD$BE$BF$BG$BH$BI$BJ$BK$BL$BM$BN$BO$BP$BQ$BR$BS$BT$BU$BV$BW$BX$BY$BZ$CA$CB$CC$CD$CE$CF$CG$CH$CI$CJ$CK$CL$CM
-rw-r--r-- 1 root system 13081 Nov 24 15:16 A.class
Main class=class A
count=91 class=A$B$C$D$E$F$G$H$I$J$K$L$M$N$O$P$Q$R$S$T$U$V$W$X$Y$Z$AA$AB$AC$AD$AE$AF$AG$AH$AI$AJ$AK$AL$AM$AN$AO$AP$AQ$AR$AS$AT$AU$AV$AW$AX$AY$AZ$BA$BB$BC$BD$BE$BF$BG$BH$BI$BJ$BK$BL$BM$BN$BO$BP$BQ$BR$BS$BT$BU$BV$BW$BX$BY$BZ$CA$CB$CC$CD$CE$CF$CG$CH$CI$CJ$CK$CL$CM$CN
A.java:93: error while writing A.B.C.D.E.F.G.H.I.J.K.L.M.N.O.P.Q.R.S.T.U.V.W.X.Y.Z.AA.AB.AC.AD.AE.AF.AG.AH.AI.AJ.AK.AL.AM.AN.AO.AP.AQ.AR.AS.AT.AU.AV.AW.AX.AY.AZ.BA.BB.BC.BD.BE.BF.BG.BH.BI.BJ.BK.BL.BM.BN.BO.BP.BQ.BR.BS.BT.BU.BV.BW.BX.BY.BZ.CA.CB.CC.CD.CE.CF.CG.CH.CI.CJ.CK.CL.CM.CN.CO: A$B$C$D$E$F$G$H$I$J$K$L$M$N$O$P$Q$R$S$T$U$V$W$X$Y$Z$AA$AB$AC$AD$AE$AF$AG$AH$AI$AJ$AK$AL$AM$AN$AO$AP$AQ$AR$AS$AT$AU$AV$AW$AX$AY$AZ$BA$BB$BC$BD$BE$BF$BG$BH$BI$BJ$BK$BL$BM$BN$BO$BP$BQ$BR$BS$BT$BU$BV$BW$BX$BY$BZ$CA$CB$CC$CD$CE$CF$CG$CH$CI$CJ$CK$CL$CM$CN$CO.class (A file or path name is too long.)
static class CO {
^
1 error
The generated Java source looks like:
生成的 Java 源代码如下所示：
class A {
static class B {
void run() {
System.out.println("count=" + 2 + " class=" + B.class.getName() + "\n");
}
}
public static void main(String[] a){
System.out.println("Main class=" + A.class + "\n");
(new A.B()).run();
}
}
回答by anil
Yes you can nest a class infinitely in Java.
是的，您可以在 Java 中无限嵌套一个类。
