InterConnect 2015 Session 3978 Why is Java so different... A Session for Cobol/PLI/Assembler Developers. After giving sessions about Java in the past few years that tell System Programmers they should do Java on System z and that Java is just like every other language, this session tries to explain why Java is a bit different in Operating and Handling. Therefore this session tries to compare COBOL/PLI/Assembler with Java and how the Java technology works on System z: > Why can't you phase in a Java Program > How is a JIT working > Understand the Development Process of Java Applications > Debugging and Logging of Java Applications > and a lot more...

1. © 2015 IBM Corporation
© IBM Corporation 2011
Why are you so different?
Java for COBOL Developers
Tobias Leicher |
CICS Client Technical Professional |
tobias.leicher@de.ibm.com

2. © 2014 IBM Corporation
IBM

3. © 2014 IBM Corporation
IBM
Goal of this Session
 After running around and shouting „Java is just another language running on the
mainframe“, it is now time to show you some lies about my fact.
 Understand differences and reasons for them
 See the advantages of different languages and also understand that there is no
single language that rules the world
 Get a feeling why problems in Java are different and a Dump in classical sense
often leads you nowhere
 Give Java another chance, that guy is now grown up and in his twenties, probably
the time in life where you have enough experience to solve the important
problems in life

4. © 2014 IBM Corporation
IBM
Before we compare, let us rethink what we know already
 Today we will talk about COBOL, PLI or even Assembler (LE) and we will
compare it to Java, as I am a CICS Person I will talk more about CICS than IMS
or Batch
 So how does a COBOL Program executes in zOS (only cover LE here):
» The first thing that happens is a load of the program:
○ In CICS the LOADER will issue a BLDL or LLACOPY MACRO against MVS and the Program is
loaded into the storage
» If you then Call the Program a new LE Enclave is----------------
○ Wait, what is this LE guy used for again?!

5. © 2014 IBM Corporation
IBM
LE – The standardized Runtime Environment in zOS
 Before LE all Languages brought their own Runtime Libraries
 A Runtime library brings all the code that is provided by a language and not part
of the user Program (Storage management, Math functions...)
 A Runtime library has the advantage, that the code is always tied to the
underlying hardware, without letting the compiler or the application do too much
adaptions
 Why now LE?
» When all the languages brought their own runtime, they expected to be alone in the world
» Customers had problems to run different languages side by side
 Back to our Topic!

6. © 2014 IBM Corporation
IBM
Before we compare, let us rethink what we know already
 Today we will talk about COBOL, PLI or even Assembler (LE) and we will
compare it to Java, as I am a CICS Person I will talk more about CICS than IMS
or Batch
 So how does a COBOL Program execute in zOS (only cover LE here):
» The first thing that happens is a load of the program:
○ In CICS the LOADER will issue a BLDL or LLACOPY MACRO against MVS and the Program is
loaded into the storage
» If you then Call the Program a new LE Enclave is initialized
○ initial storage is obtained
○ condition handlers initialized
○ active member language specific run-time is initialized
» Control is given to the application code
» Once the application ends and 'returns' to LE
○ The LE environment is terminated
○ System resources obtained during initialization and throughout the execution of the application are
cleaned up

7. © 2014 IBM Corporation
IBM
How does that look like?
= CICS Region
= CICS initial transaction
= Main Transaction
Program
or EC Linked
Program

8. © 2014 IBM Corporation
IBM
So what does the storage in LE look like?

9. © 2014 IBM Corporation
IBM
CICS AS
How is a program dispatched then in CICS (abstracted)
zOS
Dispatcher
WEB
SWUQ
WEB WEB WEB
Global
SRB
TCB
ASCB
CICS
DFHSIP
TCB
OTE
TCB
OTE
LE Enclave LE Enclave
WEB
TCB
QR
CICS
Dispatcher
LE Enclave LE Enclave
RTRQ

10. © 2014 IBM Corporation
IBM
So in CICS a Task has one or more LE Enclaves that are totally
seperated from each other Task in the address space
 What happened with this great concept?!

11. © 2014 IBM Corporation
IBM
Once upon a time...

12. © 2014 IBM Corporation
IBM
Everyone knew where to put their application, but suddenly things were
different...

13. © 2014 IBM Corporation
IBM
Soon the workload starts spreading...

14. © 2014 IBM Corporation
IBM
Everyone was confused...

15. © 2014 IBM Corporation
IBM
And the new and shiny PC world was different to the Mainframe!
 Less Users
 Bad code has far more resources on its own
 Coding Style Changed a lot
 No LE, not even a unified Operating System (And Yes I know we have VM, VSE,
TPF and Linux on the mainframe as well)
 Backward Compatibility was not given anymore
 ...

16. © 2014 IBM Corporation
IBM
History of programming languages
1954 1959 1964 1971
SmallTalk
PL/I
COBOL
Fortran
1983
C
C++
LISP
Basic
1989
Perl
1995
OAK Java
JavaScript

17. © 2014 IBM Corporation17 March 6, 2015
IBM
What is Java and what makes it different from what we have today
Java is What makes Java different
Java differes in some parts quite a lot from traditional
languages like assembler, PL/I or COBOL
 Java is NOT compiled to executable code, it is
compiled to bytecode, that runs in a virtual machine
 The virtual machine uses the just-in-time compiler (JIT)
to execute the code
 Java is not based on programs, it is based on classes
 Java uses a garbage collector, that removes unused
objects from the storage
 Java development is often based on exiting
programming patterns (Design Patterns)
 Most of the build in funtionality of Java is based of
class libraries, that are build in the Java Runtime (JRE)
 Java contains a library for user interface development
 Java has the ability to reflect about the runtime with
several methods
 Java has a type safe variable declaration
 Uses JNI for native system calls and JDBC for
database calls
Java is
 an object oriented,
 platform independent,
 broadly supported and prevalent
 an state of the art language
 [and an Island in Indonesia]
 Something YOU should care about
Java is not
 something new and not reliable
 an error-prone language
 the only solution for good code
 independent on it's own
 something that the distributed world should care of
 easy and/or out of the box
 a composable workbox full of libraries

18. © 2014 IBM Corporation18 March 6, 2015
IBM
Java on Mainframes - what is different and why here?
 IBM uses its own implementation of a
JVM on mainframes that uses the
underlying platform architecture
 The Java workload can be offloaded
to a zAAP processor
 The Java logic can be a bridge
between the mainframe and the
distributed world
 Java is a common language on many
platforms that can help to find a dialog
between the departments
 Java is a language that is well known
by many new professionals and so a
good common ground, when they
start to develop for mainframe
IBM JDK for z/OS
Standard JSE
(JDK specification)
zOS
Extensions
Just In Time Compiler (JIT)
Exploitation of the Hardware Architecture
z/OS Operating System
and System z Hardware

19. © 2014 IBM Corporation19 March 6, 2015
IBM
Java packaging and class hierarchies
 Java modularity:
–Classes contain data and logic
–Packages contain these classes and
organize them
• This is just a virtual form of organization
–Jar files contain the classes and are the
base for enterprise applications
 Java visibility settings:
–Private, protected, package private,
public
 At the runtime, there are just a lot of
classes on a classpath
jar file
java packages
class files
There are some features missing: jar visibility, versioning, dependencies

20. © 2014 IBM Corporation20 March 6, 2015
IBM
The Classpath – What was called a load lib concatenation before
Java VM
log4j
barcode4j
axis
batik
commons
derby
fop
ezmorph
freemarker
httpunit
jakarta
jcl
json
jdbm
jdom
jenks
jpos18
jython
looks
lucene
mail
mx4j
naming
jetty
poi
resolver
rome
serializer
servlets
tomcat
velocity
ws-commons
xalan
wsdl4j
xerces
xmlgraphics
xmlrpc
xmlapis
..
geronimo
bsh
bsf
guiapp
hhfacility
manufact.
marketing
minerva
accounting
assetmaint
base
bi
catalina
common
oagis
order
ebay
content
datafile
ecommerce
entity
googlebase
ofbiz
widget
minilang
party
pos.
product
workeffort
workflow
…
sunjce_prov.
plugin
jsse
jce
rt
dnsns
..
…
Class
Not
Found
Exception
BeginBegin
HereHere

21. © 2014 IBM Corporation
IBM
Specialty CP operation
 Eligible work moves to specialty CP under control of z/OS
 Provide more capacity for eligible workloads without a change in MSU
 Provides more capacity for non-eligible workloads
 Reduces software stack charges for non-eligible products on CEC
Eligible
work
Eligible
work
Eligible
work
Eligible
work
Eligible
work
Eligible
work
GCP zIIPGCP

22. © 2014 IBM Corporation
IBM
IBM System z Application Assist Processor (zAAP)
Dedicated to execution of Java workloads under z/OS®
– e.g. Websphere®
, CICS, IMS, DB2®
 Available on all IBM zEnterprise
systems, System z9 and z10 and
zSeries z990 and z890
 Used by any workload with Java
cycles
 Executes java code without any
changes to the applications
 Also used for XML parsing
Standard CP zAAP
WebSphere
Execute JAVA Code
z/OS Dispatcher
Suspend JVM task on z/OS
standard logical processor
WebSphere
Java Application Code
Executing on a zAAP
logical processorz/OS Dispatcher
JVM
Switch to zAAP
JVM
JVMSwitch to
z/OS Dispatcher
JVM
Dispatch JVM task on z/OS
standard logical processor
JVM
z/OS Dispatcher
logical processor
z/OS Dispatcher
Dispatch JVM task on z/OS
zAAP logical processor
JVM
Switch to standard processor
z/OS Dispatcher
Suspend JVM task on z/OS
standard logical processor

23. © 2014 IBM Corporation
IBM
So now let us see what happens in Java
 Everything in Java is executed within a virtual machine
 Run Time Data Management is done by the virtual machine
 The JVM will only stop if the last non-deamon thread finishes
 Java is never compiled upfront, it is interpreted and compiled during runtime
» Do you remember HPJ?
 Java is platform independent, so everything in Java is abstracted (including
Datatypes

24. © 2014 IBM Corporation
IBM
Lets dive a bit deeper
Source: http://www.artima.com/insidejvm/ed2/jvmP.html

25. © 2014 IBM Corporation
IBM
How does a Java LE-Enclave look like
C main procedure (JVM)
LE Thread
Native
Stack
LE Heap Storage
Java Heap
Java Stack Classes
JIT Data

26. © 2014 IBM Corporation
IBM
If we have a look at the LE Config for Java in CICS (DFHAXRO)
 The LE Enclave is configured to always obtain new Heap Storage
» Bare in Mind that the JVM Heap Size is managed by the JVM, so a JVM can run out of
memory
» initial 64-bit heap of 100MB
» initial 31-bit heap of 4MB
» Both areas allow incremental expansion to increase
 The Files generated by the JVM are controlled by:
» DC C'ENVAR("_EDC_UMASK_DFLT=nnn")'
 The output that is produced by the RPTO and RPTS options is written to the
CESE transient data queue

27. © 2014 IBM Corporation
IBM
CICS AS
So how is Java now executed in CICS (abstracted)
zOS
Dispatcher
WEB
SWUQ
WEB WEB WEB
Global
SRB
TCB
ASCB
CICS
DFHSIP
TCB
OTE
TCB
OTE
Java LE Enclave
JVM Thread
WEB
TCB
QR
CICS
Dispatcher
LE Enclave LE Enclave
RTRQ
JVM Thread
JVM Thread
pThread
pThread

28. © 2014 IBM Corporation
IBM
What happens when a class got loaded

29. © 2014 IBM Corporation
IBM
What happens in the different phases
 Loading: A class is obtained from a file and loaded to the JVM memory.
 Verifying: Check whether or not the read class is configured as described in the
Java Language Specification and JVM specifications. This is the most
complicated test process of the class load processes, and takes the longest time.
Most cases of the JVM TCK test cases are to test whether or not a verification
error occurs by loading wrong classes.
 Preparing: Prepare a data structure that assigns the memory required by classes
and indicates the fields, methods, and interfaces defined in the class.
 Resolving: Change all symbolic references in the constant pool of the class to
direct references.
 Initializing: Initialize the class variables to proper values. Execute the static
initializers and initialize the static fields to the configured values.

30. © 2014 IBM Corporation
IBM
So what happens higher above in the Compiler
 The Java Bytecode for the following method:
 Compiles to (javap -c):
public int sum(int a, int b) {
int result = 0;
result = a + b;
return result;
}
public int sum(int, int);
Code:
0: iconst_0
1: istore_3
2: iload_1
3: iload_2
4: iadd
5: istore_3
6: iload_3
7: ireturn

31. © 2014 IBM Corporation
IBM
Some more details (javap -v):
public int sum(int, int);
flags: ACC_PUBLIC
Code:
stack=2, locals=4, args_size=3
0: iconst_0
1: istore_3
2: iload_1
3: iload_2
4: iadd
5: istore_3
6: iload_3
7: ireturn
LineNumberTable:
line 12: 0
line 13: 2
line 14: 6
LocalVariableTable:
Start Length Slot Name Signature
0 8 0 this Lorg/leicher/java/samples/HelloWorldSum;
0 8 1 a I
0 8 2 b I
2 6 3 result I

32. © 2014 IBM Corporation
IBM
What happens now with this bytecode?
 The JVM constructs for each Thread an execution engine
 In this engine the application now needs to be executed
» Problem?
○ The JVM interpreting bytecodes can’t match the performance of native applications with machine
code
○ Need to improve the performance of JVM startup (interpreting/compiling) and Java applications
over the life of JVM
» Solution!
○ A compiler that will allow JVM to start reasonably quickly
○ JIT code optimization processes
○ Improve overall Java applications performance
 The JIT Frontend is common in all IBM JVM Implementations, the Backend is
specific to system z

33. © 2014 IBM Corporation
IBM
A Glance at JIT and the Interpreter
Java Application
JVM
JIT
Compiler
J9
Interpreter

34. © 2014 IBM Corporation
IBM
The Memory Management of the JVM
Heap Method Area Native Area
Young Generation Old Generation
Virtual
From
Survivor0
To
Survivor1
Eden
Tenured
Virtual
Permanent Generation
Runtime Constant
Pool
Field & Method Data
Code
Virtual
Code Cache
Native
Compile
Threads (1..N)
Virtual
PC
Stack
Native
Stack
-Xmx
NrGCEvents

35. © 2014 IBM Corporation
IBM
So where are now the data of an Object
Heap
● Object HelloWorld
● Object SimpleDateFormat
● Object String
● Object LOGGER
Method Area
● Class SimpleDateFormat
● …
● Class Logger
● …
● Class HelloWorld
● Method: sayHello()
● ...
Native Area
● Parameter reference:
“message” to String
object
● Variable references
● “formatter”
● “today”

36. © 2014 IBM Corporation37
IBM
Compare Cobol to Java
Develop a COBOL program
 Cobol does not know complex DataTypes or Objects
 Data Elements are usually shared, not hidden
 The compile is usually done after coding (no online
syntax checking)
 Compiler perform less static tests
 Debugging is done in Multiuser Environments
Runtime Behaviour of Cobol
 LE does not check wether the loaded program is
corrupt
 The runtime can not check whether the data is
assigned correctly and Problems can arise
 Handlers get control if something went wrong
 Memory is defined upfront
Develop a Java program
 Data is structured in complex Objects
 Variables are not shared, they are adressed by
methods of the object
 Compiles are executed everytime a class is saved
(while ongoing syntax check is performed)
 Compiler performs a lot of static testing
 Debugging is usually done locally
 Memory can NEVER be addressed directly
Runtime Behaviour of Java
 The JVM checks the bytecode after loading the class
 Classes are checked during compilation and in
Runtime data is only assigned if types match
 Classes and methods can throw exceptions (also JNI)
if a problem occurs
 New Objects can be generated very dynamical

37. © 2014 IBM Corporation38
IBM
Update Behavior – “Java, why can't I just phase you in?”
Update a COBOL Program in CICS
 COBOL Program is compiled/linked into a PDSe that
is concatinated into the RPL upfront the existing Load
Library or replace the existing version
 In CICS issue a NEWCOPY or PHASEIN to let CICS
reload the Program from the Dataset
 Use the new Program
Update a Java Program in CICS
 In Java you can't replace runtime code (except via
JDWP)
 Frameworks like OSGi enables the exchange of
bundles
 You need to decouple the application desing (using
micro Services in OSGi or accept a small outage
Problems with this Approach
 Compatibility is a contract that is not checked until
runtime
 The connection is something the compiler is not
aware of
Problems with this Approach
 The simple Phasein/Newcopy is not possible
 A complex Build infrastructure is necessary
 Only bundles/services, not classes can be “phased in”
 A change in Application Development Architecture is
necessary

38. © 2014 IBM Corporation39
IBM
Questions
Tobias Leicher
Client Technical Professional & zChampion
– CICS & CICS Tools
IBM Allee 1
D-71139 Ehningen
Mobil: 0151 – 15 16 24 89
Mail: tobias.leicher@de.ibm.com
Foto
VIELEN DANK FÜR IHRE AUFMERKSAMKEIT.

39. What’s next…
More of my sessions
#ASZ-3983: CICS Java Real-Life Projects, Featuring Datev
#ASZ-3978: Why Is Java So Different?: A Session forCobol/PLI/AssemblerDevelopers
#ASZ-5927: Meet the Experts of Generation z—Driving Innovation on the Mainframe
More Cloud sessions
#ASZ-2829: Liberté, Égalité, Fraternité—Viva the CICS and WebSphere Mini Revolution
#ASZ-6481: Java and CICS—A Perfect Match
#ASZ-1841: WebSphere Liberty Profile Support forJava Batch and the JSR-352 Specification, Featuring
Sicoob
Collect a z Passport stickerhere, and at…
@IBM_CICS slideshare.net/IBM_CICSfacebook.com/IBMCICS ibm.com/cics
WIN!

40. Get a lightning start: Key InterConnect 2015 sessions
#2829 Mon 2:00-3:00 Liberté, Égalité, Fraternité—Viva the CICS and WebSphere Mini Revolution
#1670 Tue 3:30-4:30 IBM WebSphere Liberty z/OS Connect: A Technical Introduction
#4032 Wed 9:30-10:30 Meet the Winners of IBM’s Mainframe Mobile App Throwdown 2014
#6482 Thu 11:00-11:50 What is the Mainframe Mobile App Throwdown and How Do I Register?
Registernow at
ibm.biz/mmathrowdown
and submit yourapp by April 12th
Mobilize yourmainframe in our fun app-building contest for
z Systems clients & business partners!
The Mainframe Mobile App Throwdown
is back for 2015!

41. Need expert help?
42
CICS Development Services, for worldwide services assistanceCICS Development Services, for worldwide services assistance
Bringing CICS development expertise directly to your doorstep
Email us CICSDTS@UK.IBM.COM
Bringing CICS development expertise directly to your doorstep
Email us CICSDTS@UK.IBM.COM
Get a deep dive into your systems with a
CICS health check
Get a deep dive into your systems with a
CICS health check
Want to know more about CICS and
Java? We offer tailored Java education
Want to know more about CICS and
Java? We offer tailored Java education
Move forward with mobile with our
customized mobile workshop
Move forward with mobile with our
customized mobile workshop
Soar into the cloud with our
tailored cloud workshop
Soar into the cloud with our
tailored cloud workshop
Need to optimize your systems? Then
ask about a performance optimization
engagement
Need to optimize your systems? Then
ask about a performance optimization
engagement
Get the low down on performance with a
CICS performance workshops
Get the low down on performance with a
CICS performance workshops
Need to modernise your workload in
CICS? Ask about a integration and
connectivity engagement
Need to modernise your workload in
CICS? Ask about a integration and
connectivity engagement
Need some help upgrading to the latest
release? Then ask about our upgrade
workshop
Need some help upgrading to the latest
release? Then ask about our upgrade
workshop
Need to reduce cost by optimizing your
systems? Then a performance
optimization engagement may be for you
Need to reduce cost by optimizing your
systems? Then a performance
optimization engagement may be for you
Need something different? Then we can
build a customized workshop, just for
you!
Need something different? Then we can
build a customized workshop, just for
you!
Availability a concern? Then try our High
Availability workshop
Availability a concern? Then try our High
Availability workshop
Visit ibm.com/cics
then click ‘Services’

42. Thank You
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Important!
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CONNECT Attendee Portal to complete
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43. Notices and Disclaimers
Copyright © 2015 by International Business Machines Corporation (IBM). No part of this document may be reproduced or transmitted in any
form without written permission from IBM.
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Information in these presentations (including information relating to products that have not yet been announced by IBM) has been reviewed for
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opportunity. IBM products and services are warranted according to the terms and conditions of the agreements under which they are provided.
Any statements regarding IBM's future direction, intent or product plans are subject to change or withdrawal without notice.
Performance data contained herein was generally obtained in a controlled, isolated environments. Customer examples are presented as
illustrations of how those customers have used IBM products and the results they may have achieved. Actual performance, cost, savings or
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