Some important issues

1. Giacomo Veneri http://jugsi.blogspot.com1
Just to drink a cup of coffee
maybe you don't know … about java
• Java
– Passing by reference or by
value (final keyword)
– stricftp keyword
– Equals .. be caught
• Java EE
– Do NOT override java.library.path
on application server
– Transient work on cluster
• Use Collection
Efficiently
• Multithreading
– TimeZone is synchronized
– DateFormat is NOT thread safe
– Loggings should be synchronized
– Volatile keyword

2. Giacomo Veneri http://jugsi.blogspot.com2
Java: passing parameter by
reference or by value?
public void myMethod(MyObject a, int b) {
a.setInternalValue(“mystring”);
b++;
}
• Formally speaking: java passes parameter by value.
• However: experienced programmers know that the code listed here will modified the status of 'a' outside the scope of
the method and b will NOT changed outside the scope of the method.
• Indeed java passes for b the value of b and for a the value of the refrence to a instance.
• Then: java passes the value of parameters on both cases.
• Suggestion: consider the final keyword, to use im-mutable object or to make a copy before calling the method.

3. Giacomo Veneri http://jugsi.blogspot.com3
Java: stricftp
public strictfp double callBystrictFP(double a) {
return (a / 2 ) * 2 ;
}
..
callBystrictFP(Double.MIN_VALUE); // it will return 0 instead of
6..E-341
• Formally speaking: FP-strict expressions must be those predicted by IEEE
754 arithmetic on operands represented using single and double formats
• However: from 1.2 java implementation of FP arithmetic is platform dependent
• Then: to ensure IEEE 754 arithmetic use strictfp
• Suggestion: if you are an ERP programmer consider BigDecimal and
MathContext for approximation, it should save your life

4. Giacomo Veneri http://jugsi.blogspot.com4
Java: equals
byte b = 'a';
byte c = 'a';
String s = “a”;
s.equals(b); //return false
s.equals(c); //return false
b == c; //return true
s ==”a”; //return true
•Formally speakingFormally speaking: Object.equals return false when the object's classes
are different, value (or refrence) are different
•HoweverHowever: litterals or charecter/integer between 0..128 could surprise us
due to java optimization
•SuggestionSuggestion: use equals for Object or primitive wrapper and “==” for
primitive
•RemeberRemeber: when you re-implement equals on your own class re-implement also
hashCode() method

5. Giacomo Veneri http://jugsi.blogspot.com5
Java: init
class MyClass {
public MyClass() {
//constructor
}
{
//init before constructor
}
}
• Formally speaking: the block
highlighted is callde before the
constructor

6. Giacomo Veneri http://jugsi.blogspot.com6
MT: SimpleDateFormat
static DateFormat df = new SimpleDateFormat(“yyyy.MM.dd G
'at' HH:mm:ss z”);
…
df.parse(..);
• Formally speaking: SimpleDateFormat is not thread safe
• Then: if you declare SimpleDateFormat static or on a singletone class on Multi Thread enviroment
(EJB, Web,...) you will experience the most absurd bug of your life
• Suggestion: do NOT declare SimpleDateFormat as attribute or static member of your class

7. Giacomo Veneri http://jugsi.blogspot.com7
MT: logging
• Some frameworks such as log4j or
logback block execution (synchronization)
to write into a file.
• Suggestion: consult logback or log4j
documentation to use Async Logging

8. Giacomo Veneri http://jugsi.blogspot.com8
MT: volatile
volatile MyCache cache = null;
public MyCache getCache() {
if (cache ==null) ||
(elapsed(cache)) {
synchronized(this) {
if (cache ==null) {
… // create cache
}
}
} else return cache;
}
• Formally speaking: thread should save local
variable on thread stuck
• Then: if another thread acquire the lock and modify
the local variable the second thread could NOT see
the change
• Suggestion: volatile force s the thread to read the in
memory variable; volatile reduces performance
(1:10)
• Reference: look for “double check” on google

9. Giacomo Veneri http://jugsi.blogspot.com9
JEE: java.library.path
• When you need to connect your java EE application to an EIS you must use JCA
–Connector Architecture (JCA) is a Java-based technology solution for connecting application
servers and enterprise information systems (EIS)
• However: if you are too lazy to implement your JCA component you might be tempted to
declare the java.library.path to point your native library
• Then: you can overwrite the native library used by your application server
–Weblogic uses java.library.path to pint native io in order to improve performance
• Suggestion: use JCA …. or …. find java.library.path of your application server and adjust it
–Be caught! On multi server or cluster environent you can modify the entire behavior

10. Giacomo Veneri http://jugsi.blogspot.com10
MT: transient
@EJB
transient MyEjb myEjb;
• Formally speaking: using transient java doesn't serialize the object, rseources
(Connection or EJB) on JEE cannot be serialized
• Then: on Migratable server two node could share session each other
• Suggestion: use transient when you reference resources

11. Giacomo Veneri http://jugsi.blogspot.com11
java.util collection
efficiency from 10 to 1
10 new HashMap()
08 new TreeMap()
03 new Hashtable(n) :
synchronized and define capacity
02 new Hashtable() :
synchronized
01
Collections.synchronizedMaps
(new HashMap())
01
Collections.synchronizedColle
ctions(new ArrayList())
03 new Vector(n) :
synchronized and define
capacity
02 Vector : synchronized
10 Iterator, Enumeration
09 new ArrayList(n): define capacity
08 new ArrayList()
07 new LinkeList(n) : manage queue
and define capacity
06 new LinkeList() : manage queue
05 new HashSet() : prevent duplicate
04 new TreeSet() : implements sorting

12. Giacomo Veneri http://jugsi.blogspot.com12
java.util collection
The given table is just a reference to take in
consideration but Map and set are not comprable ...
1.Use ensureCapacity for better performance to write
data
2.Performance of LinkedList decreases when size
increases
3.Iterator is faster than “for cycle” over set, but, on Map,
when you ned to create iterator by keySet, doesn't
produce any valuable difference

13. Giacomo Veneri http://jugsi.blogspot.com13
Quiz ;-)
• How many issues did you know
– 3 maybe you are 3 year experienced programmer
– 5 maybe you are 5 year experienced programmer
– 7 maybe you are junior JEE architect
– 10 you are senior JEE architect
– ..or maybe not

14. 16/07/13 Giacomo Veneri - http://jugsi.blogspot.com14
Giacomo Veneri, PhD, MCs
(IT Manager, Human Computer Interaction Scientist)
@venergiac
g.veneri@ieee.org
http://jugsi.blogspot.com
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