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<title>RE: Porovnani v Jave</title>
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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> Zdravím,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> Nejedná se přímo o
předgenerované typy, ale o tzv. IntegerCache, do které se ukládají objekty typu
int právě v rozsahu -128 až 127, podívejte se sem:<o:p></o:p></span></font></p>
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10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> <a
href="http://www.docjar.com/html/api/java/lang/Integer.java.html">http://www.docjar.com/html/api/java/lang/Integer.java.html</a><o:p></o:p></span></font></p>
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10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> Hledejte třídu:<o:p></o:p></span></font></p>
<pre><a name=591><font size=2 face="Courier New"><span style='font-size:10.0pt'> private static class IntegerCache</span></font></a><o:p></o:p></pre>
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10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<pre><font size=2 color=navy face=Arial><span style='font-size:10.0pt;
font-family:Arial;color:navy'> resp. její použití v metodě </span></font><a
name=631>public static Integer valueOf(int i) </a>hned za definicí této třídy (přibližně uprostřed souboru).<o:p></o:p></pre><pre><font
size=2 face="Courier New"><span style='font-size:10.0pt'><o:p> </o:p></span></font></pre><pre><font
size=2 face="Courier New"><span style='font-size:10.0pt'> M.Kalina, Brno<o:p></o:p></span></font></pre>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> <o:p></o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> hw-list-bounces@list.hw.cz
[mailto:hw-list-bounces@list.hw.cz] <b><span style='font-weight:bold'>On Behalf
Of </span></b>Jiří Vojtek<br>
<b><span style='font-weight:bold'>Sent:</span></b> Thursday, August 23, 2012
12:21 PM<br>
<b><span style='font-weight:bold'>To:</span></b> '<st1:PersonName w:st="on">HW-news</st1:PersonName>'<br>
<b><span style='font-weight:bold'>Subject:</span></b> RE: Porovnani v Jave</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p style='margin-bottom:12.0pt'><font size=2 face="Times New Roman"><span
style='font-size:10.0pt'>Je to proto, ze tyto hodnoty existuji jako
predgenerovane objekty :)<br>
Protoze v Jave je vsechno objekt. Pokud date cislo vyssi tak se ten objekt<br>
teprve vytvori, ale pro zvyseni rychlosti pro mala cisla uz to je<br>
predvarene.<br>
J.V.<br>
<br>
-----Original Message-----<br>
From: hw-list-bounces@list.hw.cz [<a href="mailto:hw-list-bounces@list.hw.cz">mailto:hw-list-bounces@list.hw.cz</a>]
On<br>
Behalf Of RV<br>
Sent: Thursday, August 23, 2012 11:32 AM<br>
To: <st1:PersonName w:st="on">HW-news</st1:PersonName><br>
Subject: Porovnani v Jave<br>
<br>
Zdravim,<br>
<br>
snazim se doucit nejak systematicky Javu a pri probirani operatoru jsem<br>
narazil na toto:<br>
<br>
Integer i = 5;<br>
Integer i2 = 5;<br>
System.out.println(i == i2);
//true<br>
<br>
Integer i3 = 128;<br>
Integer i4 = 128;<br>
System.out.println(i3 == i4);
//false<br>
<br>
ja vim, ze se to takto delat nema, ze je na to treba pouzivat metodu equals,<br>
ale jak k tomu vyhodnoceni ten zatracene javovskej VM dospeje!<br>
<br>
Zkousel jsem to opravdu spustit a je to opravdu tak.<br>
<br>
Do hodnoty 127 oboji vraci true. Zrejme to souvisi s obalenim objektovym<br>
wraperem Integer - zrejme se tedy nevraci hodnota ale jen odkaz na instanci,<br>
ktera samozrejme neni stejna. Ale proc to proboha je jen v tom rozsahu<br>
-128/127.<br>
<br>
--<br>
Radek Vicek<br>
<br>
<br>
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