+
−.. -*- coding: utf-8; -*-
+
−.. include:: HEADER.rst
+
−
+
−================
+
− Java language.
+
−================
+
−.. contents::
+
−
+
−Class version.
+
−==============
+
−
+
−  =========  ====== =====================
+
−  major      minor  Java platform version
+
−  =========  ====== =====================
+
−  45 0x27    3      1.0
+
−  45 0x27    3      1.1
+
−  46 0x28    0      1.2
+
−  47 0x29    0      1.3
+
−  48 0x30    0      1.4
+
−  49 0x31    0      5.0
+
−  50 0x32    0      6.0
+
−  51 0x33    0      7
+
−  52 0x34    0      8
+
−  =========  ====== =====================
+
−
+
−where ``minor`` and ``major`` are value of 6 and 8 bytes in .class file::
+
−
+
−  0xCA, 0xFE, 0xBA, 0xBE, 0x00, minor, 0x00, major
+
−
+
−Access modifiers.
+
−=================
+
−
+
−Public.
+
−-------
+
−
+
− * Public class is visible in other packages.
+
− * Public field is visible everywhere (class must be public too).
+
−
+
−Private.
+
−--------
+
−
+
− * Private variables or methods may be used only by an instance of the same
+
−   class that declares the variable or method
+
− * A private feature may only be accessed by the class that owns the feature.
+
−
+
−Protected.
+
−----------
+
−
+
− * Is available to all classes in the same package and also available to all
+
−   subclasses of the class that owns the protected feature.
+
− * This access is provided even to subclasses that reside in a different
+
−   package from the class that owns the protected feature.
+
−
+
−default.
+
−--------
+
−
+
−What you get by default ie, without any access modifier.
+
−
+
− * It means that it is visible to all within a particular package.
+
−
+
−static.
+
−-------
+
−
+
− * Static means one per class, not one for each object no matter how many
+
−   instance of a class might exist. This means that you can use them without
+
−   creating an instance of a class.
+
− * Static methods are implicitly final, because overriding is done based on
+
−   the type of the object, and static methods are attached to a class, not an
+
−   object.
+
− * A static method in a superclass can be shadowed by another static method in
+
−   a subclass, as long as the original method was not declared final.
+
− * You can't override a static method with a nonstatic method.
+
−
+
−final.
+
−------
+
−
+
− * A final class can't be extended ie., final class may not be subclassed.
+
− * A final method can't be overridden when its class is inherited.
+
− * You can't change value of a final variable.
+
−
+
−Exceptions.
+
−===========
+
−
+
−A checked exception is some subclass of Exception (or Exception itself),
+
−excluding class RuntimeException and its subclasses.
+
−
+
−Unchecked exceptions are RuntimeException and any of its subclasses. Class
+
−Error and its subclasses also are unchecked. With an unchecked exception,
+
−however, the compiler doesn't force client programmers either to catch the
+
−exception or declare it in a throws clause.
+
−
+
−Inner classes.
+
−==============
+
−
+
−Nested top-level classes.
+
−-------------------------
+
−
+
−If you declare a class within a class and specify the static modifier, the
+
−compiler treats the class just like any other top-level class.
+
−
+
−Any class outside the declaring class accesses the nested class with the
+
−declaring class name acting similarly to a package. eg, outer.inner. Top-level
+
−inner classes implicitly have access only to static variables. There can also
+
−be inner interfaces. All of these are of the nested top-level variety.
+
−
+
−Member classes.
+
−---------------
+
−
+
−Member inner classes are just like other member methods and member variables
+
−and access to the member class is restricted, just like methods and variables.
+
−This means a public member class acts similarly to a nested top-level class.
+
−
+
−The primary difference between member classes and nested top-level classes is
+
−that member classes have access to the specific instance of the enclosing
+
−class.
+
−
+
−Local classes.
+
−--------------
+
−
+
−Local classes are like local variables, specific to a block of code. Their
+
−visibility is only within the block of their declaration. In order for the
+
−class to be useful beyond the declaration block, it would need to implement a
+
−more publicly available interface.
+
−
+
−Because local classes are not members, the modifiers public, protected,
+
−private, and static are not usable.
+
−
+
−Anonymous classes.
+
−------------------
+
−
+
−Anonymous inner classes extend local inner classes one level further. As
+
−anonymous classes have no name, you cannot provide a constructor.
+
−
+
−64-bit problem.
+
−===============
+
−
+
−  http://www.java.com/en/download/faq/java_win64bit.xml
+
−                Which version of Java should I download for my 64-bit Windows
+
−                operating system?
+
−  http://java.sun.com/javase/6/webnotes/install/system-configurations.html
+
−                Java SE 6 Release Notes Supported System Configurations
+
−
+
−Java performance.
+
−=================
+
−
+
−  http://java.sun.com/performance/reference/whitepapers/5.0_performance.html
+
−  http://java.sun.com/performance/reference/whitepapers/6_performance.html
+
−
+
−Creating jar.
+
−=============
+
−::
+
−
+
−  $ jar cf myFile.jar *.class
+
−  $ jar cmf myManifestFile myFile.jar *.class
+
−  $ jar -cfe Main.jar foo.Main foo/Main.class
+
−
+
−Profiling Java.
+
−===============
+
−::
+
−
+
−  $ java -Xprof com.vendor.product.Clazz
+
−  $ java -Xrunhprof:help
+
−
+
−Debugging Java.
+
−===============
+
−
+
−Compile with ``-g`` to preserve source code information::
+
−
+
−  $ javac -g -cp $CLASSPATH -sourcepath $SRC_DIR -d $BUILD_DIR
+
−
+
−To run Java program in debugger::
+
−
+
−  $ jdb -cp $CLASSPATH -sourcepath $SRC_DIR
+
−
+
−To attach to Java application you firstly must run application with (use
+
−``dt_shmem`` for Windows and ``dt_socket`` for Linux)::
+
−
+
−  $ java -Xdebug -Xrunjdwp:transport=dt_shmem,server=y,suspend=n,address=$PORT \
+
−    com.vendor.product.Clazz
+
−
+
−and then attach with debugger::
+
−
+
−  $ jdb -attach $PORT
+
−
+
−Dump current thread traces and memory statistic to stdout::
+
−
+
−  $ kill -QUIT $PID
+
−
+
−Debug class loading.
+
−====================
+
−
+
−To dump class loading and unloading to ``System.out`` add to ``java`` opts::
+
−
+
−  $ java -XX:+TraceClassLoading -XX:+TraceClassUnloading ...
+
−  $ java -verbose:class ...
+
−
+
−To review loaded classes explore heap dump in ``visualvm`` (visit "Classes"
+
−tab).
+
−
+
−Decompile class file.
+
−=====================
+
−::
+
−
+
−  $ javap -v -p -c My.java
+
−
+
−Find jar by class.
+
−==================
+
−
+
−  http://mvnrepository.com/search.html?query=PKG
+
−  http://www.jarfinder.com
+
−
+
−Set default Java in Debian.
+
−===========================
+
−::
+
−
+
−  $ update-java-alternatives -l
+
−  $ sudo update-java-alternatives -s java-1.8.0-openjdk-i386
+
−
+
−or individually for each executable::
+
−
+
−  $ sudo update-alternatives --config java
+
−
+
−Import SSL certificate.
+
−=======================
+
−
+
−Get cert with::
+
−
+
−  $ openssl s_client -connect promin-test.it.loc:433
+
−
+
−  -----BEGIN CERTIFICATE-----
+
−  ...
+
−  -----END CERTIFICATE-----
+
−
+
−or by opening URL in broswer and exporting in "Page info" ==> "Security" menu.
+
−
+
−Call import utility with default ``changeit`` password::
+
−
+
−  $ keytool -importcert -file $YOUR.crt -keystore $JAVA_HOME/jre/lib/security/cacert -alias $ANY -storepass changeit
+
−  $ keytool -list -v -keystore $JAVA_HOME/jre/lib/security/cacert -storepass changeit
+
−
+
−Import certificate system wide in Debian by (note, ``.crt`` extention is
+
−mandatory)::
+
−
+
−  $ sudo mkdir /usr/share/ca-certificates/$ANY/    # don't mess with other certs
+
−  $ sudo cp /tmp/$YOUR.crt /usr/share/ca-certificates/$ANY/
+
−  $ sudo dpkg-reconfigure --force ca-certificates  # check your cert in curses GUI!
+
−  $ sudo update-ca-certificates --fresh --verbose
+
−
+
−Java EE versions.
+
−=================
+
−
+
−======= ======== ======== ========
+
−Java EE Servlet  JSP      JSTL
+
−======= ======== ======== ========
+
−6       3.0      2.2      -
+
−5       2.5      2.1      1.2
+
−1.4     2.4      2.0      1.1
+
−1.2     2.3      1.2      1.0
+
−======= ======== ======== ========
+
−
+
−To set servlet version check ``WEB-INF/web.xml``::
+
−
+
−  <web-app xmlns="http://java.sun.com/xml/ns/javaee" version="3.0">
+
−
+
−See:
+
−
+
−  http://jcp.org/aboutJava/communityprocess/final/jsr315/index.html
+
−                Servlet 3.0 Specification
+
−  http://jcp.org/aboutJava/communityprocess/mrel/jsr154/index.html
+
−                Servlet 2.5 Specification
+
−  http://www.mularien.com/blog/2008/04/24/how-to-reference-and-use-jstl-in-your-web-application/
+
−                How to Reference and Use JSTL in your Web Application
+
−  http://en.wikipedia.org/wiki/Java_EE_version_history
+
−                Java EE version history
+
−
+
−Java interactive shell.
+
−=======================
+
−
+
−Just use Groovy. ``bsh`` is older alternative without code completion.