DO:
In report manager,
exporter.setParameter(JExcelApiExporterParameter.IS_COLLAPSE_ROW_SPAN, Boolean.TRUE);
In xml,
textField isStretchWithOverflow="true" // on long data input cells
reportElement stretchType="RelativeToTallestObject"
API: http://jasperreports.sourceforge.net/api/net/sf/jasperreports/engine/export/JRXlsAbstractExporterParameter.html
Thursday, September 9, 2010
Wednesday, June 9, 2010
Initialization of list/map in one line
List
ArrayList places = new ArrayList(Arrays.asList("Buenos Aires", "Córdoba", "La Plata"));
ArrayList list = new ArrayList() {{
add("A");
add("B");
add("C");
}}
link
Map
Map m = new HashMap() {
{
put(".jpg", "image/jpeg");
put(".jpeg", "image/jpeg");
}
};
ArrayList
ArrayList
add("A");
add("B");
add("C");
}}
link
Map
Map
{
put(".jpg", "image/jpeg");
put(".jpeg", "image/jpeg");
}
};
Sunday, April 11, 2010
Java Concurrency/Threads
Process vs Thread
Process - is a running program that runs independently from other processes. It has its own address space and cannot directly access resources of other processes. Each process can have one or more threads.
Thread - is sometimes called lightweight process. Both processes and threads provide an execution environment, but creating a new thread requires fewer resources than creating a new process. Threads share the process's resources, including memory and open files.
2 ways to define a Thread:
Thread methods:
Source: http://java.sun.com/docs/books/tutorial/essential/index.html
http://www.vogella.de/articles/JavaConcurrency/article.html
Process - is a running program that runs independently from other processes. It has its own address space and cannot directly access resources of other processes. Each process can have one or more threads.
Thread - is sometimes called lightweight process. Both processes and threads provide an execution environment, but creating a new thread requires fewer resources than creating a new process. Threads share the process's resources, including memory and open files.
2 ways to define a Thread:
- implement Runnable interface
- more general, can have many superclass
- starting: (new Thread(new HelloRunnable())).start(); - extend Thread class (Thread class itself implements Runnable)
- simpler but limited
- starting: (new HelloThread()).start();
Thread methods:
- public void run() - the only method coming from Runnable
- public void start() - calls the run() method, can only be called once
- public static void sleep(long millis)/(long millis, int nanos) throws InterruptedException - suspend execution for a specified period
- time is not guaranteed
- can be interrupted - public void interrupt() - indicates that thread should stop
- public static boolean interrupted() - interrupted status is cleared
- public boolean isInterrupted() - has no effect on interrupted status
- public final void stop()/suspend()/resume() - deprecated
Object | Thread |
---|---|
notify notifyAll wait | sleep yield |
Source: http://java.sun.com/docs/books/tutorial/essential/index.html
http://www.vogella.de/articles/JavaConcurrency/article.html
Thursday, April 1, 2010
Using Resource Bundle
ResourceBundle is a class used for containing locale-specific data. A Locale defines the user's environment particularly its language and region. A certain number in one locale may be written differently in another. Likewise, a label of a "Cancel" button may differ in different locales. Using ResourceBundle will allow you to handle these different locales without having to hard-code the locale-specific data.
Sample of retrieving locale-specific data
list of resource bundles:
ButtonLabel
ButtonLabel_de
ButtonLabel_en_GB
ButtonLabel_fr_CA_UNIX
selecting the locale-specific ButtonLabel resource bundle:
Locale currentLocale = new Locale("fr", "CA", "UNIX");
ResourceBundle introLabels =
ResourceBundle.getBundle("ButtonLabel", currentLocale);
2 Types of ResourceBundle
Notes:
- things to check/consider when internationalizing: http://java.sun.com/docs/books/tutorial/i18n/intro/checklist.html
- numbers, dates, times, or currencies need not be isolated in a ResourceBundle because only the display format of these objects varies with Locale, the objects themselves do not
- it is better to have multiple ResourceBundle by determining related objects and grouping them together
- ResourceBundle.Control class provides a way to control the instantiation and location of resource bundles. You can override its methods to behave differently.
- list of language codes (ISO-639): http://ftp.ics.uci.edu/pub/ietf/http/related/iso639.txt
- list of country codes (ISO-3166): http://userpage.chemie.fu-berlin.de/diverse/doc/ISO_3166.html
Source: http://java.sun.com/docs/books/tutorial/i18n/resbundle/index.html
Sample of retrieving locale-specific data
list of resource bundles:
ButtonLabel
ButtonLabel_de
ButtonLabel_en_GB
ButtonLabel_fr_CA_UNIX
selecting the locale-specific ButtonLabel resource bundle:
Locale currentLocale = new Locale("fr", "CA", "UNIX");
ResourceBundle introLabels =
ResourceBundle.getBundle("ButtonLabel", currentLocale);
2 Types of ResourceBundle
- PropertyResourceBundle - uses a properties file to contain the key-value pairs. The value can only be a String.
properties files for 3 resource bundles:
LabelsBundle.properties
LabelsBundle_de.properties
LabelsBundle_fr.properties
resource bundle sample content:
# This is the LabelsBundle_de.properties file
s1 = Computer
s2 = Platte
s3 = Monitor
s4 = Tastatur
use of resource bundle sample:
Locale[] supportedLocales = {
Locale.FRENCH,
Locale.GERMAN,
Locale.ENGLISH
};
for (int i = 0; i < supportedLocales.length; i ++) {
ResourceBundle labels =
ResourceBundle.getBundle("LabelsBundle",currentLocale);
String value = labels.getString(key);
Enumeration bundleKeys = labels.getKeys();
while (bundleKeys.hasMoreElements()) {
String key = (String)bundleKeys.nextElement();
String value = labels.getString(key);
}
} - ListResourceBundle - uses a list to contain the key-value pairs. The value can be any object.
3 resource bundles:
StatsBundle_en_CA.class
StatsBundle_fr_FR.class
StatsBundle_ja_JP.class
resource bundle sample:
import java.util.*;
public class StatsBundle_ja_JP extends ListResourceBundle {
public Object[][] getContents() {
return contents;
}
private Object[][] contents = {
{ "GDP", new Integer(21300) },
{ "Population", new Integer(125449703) },
{ "Literacy", new Double(0.99) },
};
}
use of resource bundle sample:
Locale[] supportedLocales = {
new Locale("en","CA"),
new Locale("ja","JP"),
new Locale("fr","FR")
};
for (int i = 0; i < supportedLocales.length; i ++) {
ResourceBundle stats =
ResourceBundle.getBundle("StatsBundle",currentLocale);
Integer gdp = (Integer)stats.getObject("GDP");
}
Notes:
- things to check/consider when internationalizing: http://java.sun.com/docs/books/tutorial/i18n/intro/checklist.html
- numbers, dates, times, or currencies need not be isolated in a ResourceBundle because only the display format of these objects varies with Locale, the objects themselves do not
- it is better to have multiple ResourceBundle by determining related objects and grouping them together
- ResourceBundle.Control class provides a way to control the instantiation and location of resource bundles. You can override its methods to behave differently.
- list of language codes (ISO-639): http://ftp.ics.uci.edu/pub/ietf/http/related/iso639.txt
- list of country codes (ISO-3166): http://userpage.chemie.fu-berlin.de/diverse/doc/ISO_3166.html
Source: http://java.sun.com/docs/books/tutorial/i18n/resbundle/index.html
Tuesday, March 23, 2010
Java Exceptions
Exception Objects
Kinds of Exceptions
Notes
- finally is always executed even if there is a change of control flow like when there is a return statement in try
- can you catch runtime exception? yes, you can catch any Throwable type but since the cost of checking for runtime exceptions exceeds the benefit of catching or specifying them, the compiler does not require that you catch them
- for readable code, it's good practice to append the string Exception to the names of all classes that inherit (directly or indirectly) from the Exception class
- what to use when creating your own exception: If a client can reasonably be expected to recover from an exception, make it a checked exception. If a client cannot do anything to recover from the exception, make it an unchecked exception.
Ref: http://java.sun.com/docs/books/tutorial/essential/exceptions/index.html
Throwable
'-> Error
'-> AnnotationFormatError
'-> AssertionError
'-> IOError
'-> ThreadDeath
'-> ...
'-> Exception
'-> RuntimeException
'-> ArithmeticException
'-> ArrayStoreException
'-> ClassCastException
'-> ConcurrentModificationException
'-> IndexOutOfBoundsException
'-> NullPointerException
'-> ...
'-> ClassNotFoundException
'-> CloneNotSupportedException
'-> InterruptedException
'-> IOException
'-> NoSuchMethodException
'-> ...
Kinds of Exceptions
- checked - all exceptions that are not RuntimeException
- unchecked
- Error
- RuntimeException
Notes
- finally is always executed even if there is a change of control flow like when there is a return statement in try
- can you catch runtime exception? yes, you can catch any Throwable type but since the cost of checking for runtime exceptions exceeds the benefit of catching or specifying them, the compiler does not require that you catch them
- for readable code, it's good practice to append the string Exception to the names of all classes that inherit (directly or indirectly) from the Exception class
- what to use when creating your own exception: If a client can reasonably be expected to recover from an exception, make it a checked exception. If a client cannot do anything to recover from the exception, make it an unchecked exception.
Ref: http://java.sun.com/docs/books/tutorial/essential/exceptions/index.html
Synchronized & Unsynchronized Objects
Synchronized | Unsynchronized |
---|---|
StringBuffer | StringBuilder |
Vector | ArrayList |
Hashtable | HashMap |
Monday, March 22, 2010
Setting the CLASSPATH Sys Var
To display the current
From: http://java.sun.com/docs/books/tutorial/java/package/managingfiles.html
CLASSPATH
variable, use these commands in Windows and Unix (Bourne shell): To delete the current contents of theIn Windows: C:\> set CLASSPATH
In Unix: % echo $CLASSPATH
CLASSPATH
variable, use these commands: To set theIn Windows: C:\> set CLASSPATH=
In Unix: % unset CLASSPATH; export CLASSPATH
CLASSPATH
variable, use these commands (for example): In Windows: C:\> set CLASSPATH=C:\users\george\java\classes
In Unix: % CLASSPATH=/home/george/java/classes; export CLASSPATH
From: http://java.sun.com/docs/books/tutorial/java/package/managingfiles.html
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