Tag Archives: Java

Jdeveloper Design Time issue fix

In Jdeveloper 11.1.2 we often see that the designer is going off and looks clumsy without the ‘WYSIWYG’ feature during the design time. The jspx or jsff designer in Jdeveloper will show as

To fix this we directly go and delete this directory o.j2ee.jsplib in

C:\Documents and Settings\ USER_NAME\ApplicationData \JDeveloper\system11.

Thanks to the blogger

For other version, if the file or folder does not exist then go to o.j2ee and delete or move – jsp-faces-tags-cache.xml and jsp-libraries.xml. Also delete .wlLib folder if it exists. If nothing works delete the system folder.

also make sure that the ‘Execute Tags in JSP Visual Editor’ is checked for adf components

updates from a collegue
If you have a class reference in your application folder that cannot be loaded this problem might occur

possible fixes






change the class .adf/META-INF/services/oracle.adf.view.rich.context.ExceptionHandler
or rename this file oracle.adf.view.rich.context.ExceptionHandler

Jdeveloper released

Jdeveloper released..


ADF JavaScript Partitioning

Most of the performance issue at the client side for the ADF application is related to large number of client side scripting files getting download which increases the download time and relatively degrading the performance of the application. Breaking up the JavaScript into small chunks will result in modularity but will increase the round trip.

To resolve this ADF Faces Framework comes up with a concept of partitioning of the huge JavaScript at the client side based on the components used in the pages. That means only limited number of scripts required for the page is loaded at the client which will increase the performance drastically.

ADF Faces groups the components JavaScript files into two groups namely partitions and features. These two groups are defined separately in two configuration files i.e. adf-js-features.xml and adf-js-partitions.xml.

The default files are location at

C:\oracle\Middleware\oracle_common\modules\oracle.adf.view_11.1.1\ adf-richclient-impl-11.jar\

If the application is loaded without using an explicit partitions then adf will use the configuration settings defined in the above specified files and does the partition.
By default, the partitioning is enabled for performance which can be disabled using the initial parameter in web.xml

<param-name> oracle.adf.view.rich.libraryPartitioning.ENABLED</param-name>







Now we will see how to create these files
•    Create adf-js-partitions.xml in public_html/WEB-INF folder of your application
•    Create adf-js-features.xml in src/META-INF folder of your application
•    The skeleton of these files looks like


<?xml version="1.0" encoding="utf-8"?>

<partitions> – root tag to define partitions, all partitions are defined inside this
<partition> – define the partition, any number of partition is allowed
<partition-name> – name of the partion. For example the javascript will be loaded as dnd-
<feature> – hook reference to the particular feature that defines to load the javascript for the component


<?xml version="1.0" encoding="utf-8"?>

<features> – root tag for the features, all features are defined inside this
<feature> – define the feature, any number of feature is allowed
<feature-name> – name of the feature that has to be referenced from the partition file
<feature-class> – javascript class for the component
<feature-dependency> – name of the feature which is extended by the javascript class


When you don’t have these files in place then the loaded scripts are

When you replicate the default content in your configuration files then the partition will be

Let’s have the partitions which defines only two partition forcomponent. It’s better to have AdfBootStrap and AdfCore as part of the partitions as these are the basic components and JavaScript to render some of the key components. You are free to research on these components to come up with your own core and booting features. You can get the base AdfBootStrap and AdfCore partitions and features configurations from

The partition file with the configuration and hook looks like

And the corresponding features are defined as

And when you run your page in internet explored 8 with Developer Tools on (F12) you can see in the script section that our partition is available as a separate script


If we refer to an invalid feature in the partition then we will get



You can download the pdf file of this from here

Interesting Questions

Why map is not a collection?

collection acts upon values. map acts on key value pair

Why the finalize method is protected?

Finalize method is for the JVM to execute before GC.imagine if finalize is public then any object can call directly which is not what we wanted. If you have some open connection you can write cleanup codes in the finalize method in your class and leave the rest of the work to the JVM to call the finalize method.

The finalize method is made protected for the subclass to override it or any finalize operations.

Can a finalize method be called for twice?

The finalize method is never invoked more than once by a Java virtual machine for any given object.

Any exception thrown by the <code>finalize</code> method causes the finalization of this object to be halted, but is otherwise ignored.

why the clone is protected?

clone is protected because it is something that ought to be overridden so that it is specific to the current class.It’s protected so you don’t use the one in object (it’ll just throw an exception anyway). They want you to override it in a class, then you make it public

How to convert BigDecimal to Integer?

BigDecimal b = new BigDecimal("123");

Integer i = new Integer(String.valueOf(b));

Why Serializable and Cloneable is not having anything?

Serializable and Cloneable are called marker or tag interface because they tag all derived class on purpose. Java has a default clone() method in Object class which should not be applied for all the class. So whenever user creates a class the object is not cloneable. The object is cloneable only when it has the marking of Cloneable interface. if any class implements Cloneable then it is understood by the JVM that the object is eligible for cloning and Object by default provides the cloning method this also provide the class to implement their own clone operation by making it protected

The class is marked Serializable for the JVM to understand that the class can be serialized


Java Annotations

Why do we use Annotations?

Annotations give information about the java program and is not part of the program itslf
They give inforamtion to the compiler for Compiler time processing, deployment time processing and runtime processing

Some of the annotations are


public class MyClass{}

public void myMethod(){}

public void run(){}

public void printWriter(){}

There are two types of annotations

Simple and Meta Annotations

Simple Annotations – provided by JDK5

* Override
* Deprecated
* Suppresswarnings

Meta Annotations – Annotations of Annotation

* Target
* Retention
* Documented
* Inherited

Target – target element for which the annotation is applicable

* @Target(ElementType.TYPE) – applied to any element of a class
* @Target(ElementType.FIELD) – applied to a field or property
* @Target(ElementType.METHOD) – applied to a method level annotation
* @Target(ElementType.PARAMETER) – applied to the parameters of a method
* @Target(ElementType.CONSTRUCTOR) – applied to constructors
* @Target(ElementType.LOCAL_VARIABLE) – applied to local variables
* @Target(ElementType.ANNOTATION_TYPE) – indicates that the declared type itself is an annotation type

Retention – how long the annotations should be retained

* RetentionPolicy.SOURCE – retained only at the source level and will be ignored by the compiler
* RetentionPolicy.CLASS – retained by the compiler at compile time, but will be ignored by the VM
* RetentionPolicy.RUNTIME – retained by the VM so they can be read only at run-time

Documented – should be documented in by the javadoc tool

Inherited -annotations of the parent class is inherited to the subclass

Producer and Consumer Problem

Self explanatory Producer and Consumer problem


package com.producer;

import java.util.ArrayList;

import java.util.Random;

public class Producer implements Runnable{

//Engine Batch ID reference

ArrayList engineList;

//Engine No is stored here

String str;

//Assigning the BATCH ID reference

public Producer(ArrayList engineList) {

this.engineList = engineList;



* Produce Engines


public void produce(){

//Random number for engine number

str = ""+Math.abs(new Random(System.currentTimeMillis()).nextLong());

//Only one thread can enter the BATCH for any operation

synchronized (engineList) {

//Add the Engine to the batch


//Notify all other threads that the new engine is added to the BATCH



//Print Engine Number

System.out.println("Produced :: ENGINE CHASIS NO ["+ str + "]");



public void run() {

System.out.println("Production started");

//10 Engine is to be produced

for(int i=0;i<10;i++){

try {

//Produce the engine


//Sleep for 2 seconds for the next operation


} catch (InterruptedException e) {

// TODO Auto-generated catch block







package com.producer;

import java.util.ArrayList;

public class Consumer extends Thread{

//Engine Batch ID reference

ArrayList<String> engineList;

//Engine No is stored here

String str;

//Assigning the BATCH ID reference

public Consumer(ArrayList<String> engineList) {

this.engineList = engineList;



* Consume Engines from the BATCH


public  void consume(int index) throws InterruptedException{

//Only one thread can enter the BATCH for any operation

synchronized (engineList) {

//if the Batch has no engines

while(engineList.size() == 0){

//then wait for some time until you get a new engine to consume



//If the engine is deployed to the BATCH

if(engineList.size() >= 0){

//The consume the engine from the respective position

str = engineList.get(index);



//Print Engine Number that it has been consumed

System.out.println("Consumed :: -------> ENGINE CHASIS NO ["+ str + "]" );



public void run() {

//10 Engine has to be consumed

for(int i=0;i<10;i++){

try {

//Produce the engine


//Sleep for 3 seconds for the next operation


} catch (InterruptedException e) {

// TODO Auto-generated catch block







package com.producer;

import java.util.ArrayList;

public class Main {

public static void main(String[] args) throws InterruptedException {

//ArrayList to store the produced engines - BATCH

ArrayList<String> engine = new ArrayList<String>();

//Producer taking the engine BATCH ID Reference

Producer producer = new Producer(engine);

//Consumer taking the reference of the engine BATCH ID Reference

Consumer consumer = new Consumer(engine);


Thread prodThread = new Thread(producer);

Thread conThread = new Thread(consumer);

//Starting the production


//Start Consumption




jrcmd – useful commands

JRockit jrcmd command is very useful for debugging issues i nthe JVM




the processid is 5176 here in this example

 jrcmd 5176 help

The following commands are available:




































 For more information about a specific command use 'help <command>'.

 Parameters to commands are optional unless otherwise stated.

 jrcmd 5176 print_object_summary



--------- Detailed Heap Statistics: ---------

43.4% 3565k    33273  +3565k [C

9.8% 802k    34241   +802k java/lang/String

7.9% 645k     5906   +645k java/lang/Class

5.1% 419k     1447   +419k [I

3.9% 316k    13498   +316k java/util/HashMap$Entry


8206kB total ---

--------- End of Detailed Heap Statistics ---

 jrcmd 5176 print_class_summary



- Class Summary Information starts here

class java/lang/Object

*class jrockit/vm/Memset

*class jrockit/vm/StringMaker

*class org/eclipse/swt/internal/win32/GCP_RESULTS

*class org/eclipse/swt/internal/win32/SCRIPT_FONTPROPERTIES

*class org/eclipse/swt/internal/win32/EXTLOGFONTW

*class org/eclipse/swt/graphics/TextLayout$1$MetaFileEnumProc


 jrcmd 5176 print_codeblocks



Codeblock type=0 start= 0x04750000 end=0x04760000 top=0x04750540 freelist=0

Codeblock type=2 start= 0x04770000 end=0x04790000 top=0x0478FFA3 freelist=4264

Codeblock type=2 start= 0x04DD0000 end=0x04DF0000 top=0x04DEFFEB freelist=421

Codeblock type=2 start= 0x05170000 end=0x05190000 top=0x0518FFF0 freelist=466


 jrcmd 5176 print_codegenlist



JIT queue length: 0

Opt queue length: 0

 jrcmd 5176 print_vm_state

CPU          : Intel Core 2 SSE SSE2 SSE3 SSSE3 Core Intel64

Number CPUs  : 2

Tot Phys Mem : 2136891392 (2037 MB)

OS version   : Microsoft Windows XP version 5.1 Service Pack 3 (Build 2600) (32-bit)

Thread System: Windows Threads

Java locking : Lazy unlocking enabled (class banning) (transfer banning)

State        : JVM is running

Command Line : -Denv.class.path=.;C:\Program Files\Java\jre6\lib\ext\QTJava.zip -Dapplication.home=C:\Program Files\Java\jrockit-jdk1.6.0_20-R28.1.0-4.0.1 -client -Dsun.java.launcher=SUN_STANDARD com.jrockit.mc.rcp.start.MCMain


GC Strategy  : Mode: pausetime, with strategy: singleconcon (basic strategy: singleconcon)

GC Status    : OC is not running. Last finished OC was OC#41.

Heap         : 0x10040000 - 0x12E78000  (Size: 46 MB)

Heap History : OC#14      - 0x11040000  (16 MB -> 19 MB; +3280 KB)

: OC#18      - 0x11374000  (19 MB -> 24 MB; +4400 KB)

: OC#21      - 0x117C0000  (24 MB -> 27 MB; +3320 KB)

: OC#26      - 0x11AFE000  (27 MB -> 32 MB; +5480 KB)

: OC#27      - 0x12058000  (32 MB -> 39 MB; +6576 KB)

: OC#28      - 0x126C4000  (39 MB -> 46 MB; +7888 KB)

Compaction   : (no compaction area)

Allocation   : TLA-min: 2048, TLA-preferred: 16384 TLA-waste limit: 2048

CompRefs     : References are 32-bit.

Loaded modules:

00400000-0043afff  C:\Program Files\Java\jrockit-jdk1.6.0_20-R28.1.0-4.0.1\bin\jrmc.exe

7c900000-7c9b1fff  C:\WINDOWS\system32\ntdll.dll


 jrcmd 5176 print_properties



=== Initial Java properties: ===

java.vm.specification.name=Java Virtual Machine Specification


java.home=C:\Program Files\Java\jrockit-jdk1.6.0_20-R28.1.0-4.0.1\jre



java.vm.info=compiled mode

=== End Initial Java properties ===

=== VM properties: ===

jrockit.vm=C:\Program Files\Java\jrockit-jdk1.6.0_20-R28.1.0-4.0.1\jre\bin\jrockit\jvm.dll

jrockit.vm.dir=C:\Program Files\Java\jrockit-jdk1.6.0_20-R28.1.0-4.0.1\jre\bin\jrockit

=== End VM properties ===

=== Current Java properties: ===

Could not find fields=== End Current Java properties ===

 jrcmd 5176 print_threads



===== FULL THREAD DUMP ===============

Thu Jan 27 11:27:48 2011

Oracle JRockit(R) R28.1.0-123-138454-1.6.0_20-20101014-1351-windows-ia32

"Main Thread" id=1 idx=0x4 tid=3836 prio=6 alive, in native

at org/eclipse/swt/internal/win32/OS.WaitMessage()Z(Native Method)

at org/eclipse/swt/widgets/Display.sleep(Display.java:4281)


-- end of trace

"(Signal Handler)" id=2 idx=0x8 tid=4692 prio=5 alive, native_blocked, daemon

"(OC Main Thread)" id=3 idx=0xc tid=3512 prio=5 alive, native_waiting, daemon


-- end of trace

"Reference Handler" id=9 idx=0x2c tid=5472 prio=10 alive, native_waiting, daemon

at java/lang/ref/Reference.waitForActivatedQueue(J)Ljava/lang/ref/Reference;(Native Method)


-- end of trace

"(Sensor Event Thread)" id=10 idx=0x30 tid=2724 prio=5 alive, native_blocked, daemon

"VM JFR Buffer Thread" id=11 idx=0x34 tid=5912 prio=5 alive, in native, daemon

"State Data Manager" id=13 idx=0x38 tid=5732 prio=5 alive, sleeping, native_waiting, daemon


-- end of trace

"Start Level Event Dispatcher" id=14 idx=0x3c tid=5644 prio=5 alive, waiting, native_blocked, daemon

-- Waiting for notification on: org/eclipse/osgi/framework/eventmgr/EventManager$EventThread@0x107D7B48[fat lock]


-- end of trace

"Framework Event Dispatcher" id=15 idx=0x40 tid=4640 prio=5 alive, waiting, native_blocked, daemon

-- Waiting for notification on: org/eclipse/osgi/framework/eventmgr/EventManager$EventThread@0x10E1A6D0[fat lock]


-- end of trace

"[RJMX] JDP Client" id=17 idx=0x44 tid=5596 prio=5 alive, in native

at java/net/PlainDatagramSocketImpl.receive0(Ljava/net/DatagramPacket;)V(Native Method)

^-- Holding lock: java/net/PlainDatagramSocketImpl@0x10988A80[recursive]


-- end of trace

"Java2D Disposer" id=19 idx=0x4c tid=4352 prio=10 alive, waiting, native_blocked, daemon

-- Waiting for notification on: java/lang/ref/ReferenceQueue$Lock@0x10D0EB30[fat lock]


-- end of trace

"AWT-Windows" id=21 idx=0x54 tid=3088 prio=6 alive, in native, daemon

at sun/awt/windows/WToolkit.eventLoop()V(Native Method)


-- end of trace

"JMAPI event thread" id=27 idx=0x68 tid=5232 prio=5 alive, in native, daemon

"JFR request timer" id=28 idx=0x6c tid=6056 prio=6 alive, waiting, native_blocked, daemon

-- Waiting for notification on: java/util/TaskQueue@0x1008DCE0[fat lock]

at jrockit/vm/Threads.waitForNotifySignal(JLjava/lang/Object;)Z(Native Method)


-- end of trace

"Worker-0" id=30 idx=0x70 tid=252 prio=5 alive, waiting, native_blocked

-- Waiting for notification on: org/eclipse/core/internal/jobs/WorkerPool@0x10DD48A0[fat lock]

at jrockit/vm/Threads.waitForNotifySignal(JLjava/lang/Object;)Z(Native Method)


-- end of trace

"Local Descriptor Scanner" id=31 idx=0x74 tid=2280 prio=6 alive, sleeping, native_waiting

at java/lang/Thread.sleep(J)V(Native Method)


"JDP Stale Descriptor Detector" id=32 idx=0x78 tid=4788 prio=6 alive, sleeping, native_waiting

at java/lang/Thread.sleep(J)V(Native Method)


-- end of trace

===== END OF THREAD DUMP ===============

 jrcmd 5176 heap_diagnostics



Invoked from diagnosticcommand

======== BEGIN OF HEAPDIAGNOSTIC =========================

Total memory in system: 2136891392 bytes

Available physical memory in system: 179638272 bytes

-Xmx (maximal heap size) is 1073741824 bytes

Heapsize: 48463872 bytes

Free heap-memory: 19064600 bytes

--------- Detailed Heap Statistics: ---------

44.3% 3375k    30871   -190k [C

9.8% 745k    31818    -56k java/lang/String

8.5% 645k     5906     +0k java/lang/Class

5.5% 417k     1378     -1k [I

3.8% 292k      237     +0k [B

3.6% 272k    11637    -43k java/util/HashMap$Entry

2.4% 179k     2234    -21k [Ljava/util/HashMap$Entry;

2.3% 171k     2585     -8k [Ljava/lang/Object;

1.4% 103k     2213    -27k java/util/HashMap

1.0% 72k     3114     +0k java/util/Hashtable$Entry


7619kB total ---

--------- End of Detailed Heap Statistics ---

----- Reference Objects statistics separated per class -----

Total Reach Act PrevAct Null

----- ----- --- ------- ----

Soft References:

1456    60   0     971  425 Total for all Soft References

org/eclipse/core/internal/registry/ReferenceMap$SoftRef =>

974    12   0     962    0 Total

962     0   0     962    0 => null

12    12   0       0    0 => org/eclipse/osgi/framework/internal/core/BundleHost

java/lang/ref/SoftReference =>

430     5   0       0  425 Total

425     0   0       0  425 => null

2     2   0       0    0 => [Ljava/lang/reflect/Constructor;

1     1   0       0    0 => org/eclipse/osgi/internal/baseadaptor/DefaultClassLoader

1     1   0       0    0 => java/util/jar/Manifest

1     1   0       0    0 => java/lang/StringCoding$StringDecoder

java/util/ResourceBundle$BundleReference =>

48    40   0       8    0 Total

29    29   0       0    0 => java/util/ResourceBundle$1

11    11   0       0    0 => java/util/PropertyResourceBundle

8     0   0       8    0 => null

sun/security/util/MemoryCache$SoftCacheEntry =>

3     3   0       0    0 Total

3     3   0       0    0 => sun/security/x509/X509CertImpl

sun/misc/SoftCache$ValueCell =>

1     0   0       1    0 Total

1     0   0       1    0 => null

Weak References:

2982  2614   0     173  195 Total for all Weak References

java/lang/ref/WeakReference =>

1705  1510   0       0  195 Total

796   796   0       0    0 => java/lang/String

327   327   0       0    0 => java/lang/Class


java/util/WeakHashMap$Entry =>

1130   958   0     172    0 Total

796   796   0       0    0 => java/lang/String

172     0   0     172    0 => null


java/util/ResourceBundle$LoaderReference =>

48    48   0       0    0 Total

39    39   0       0    0 => org/eclipse/osgi/internal/baseadaptor/DefaultClassLoader

9     9   0       0    0 => java/util/ResourceBundle$RBClassLoader

java/lang/ThreadLocal$ThreadLocalMap$Entry =>

38    38   0       0    0 Total

20    20   0       0    0 => java/lang/ThreadLocal

11    11   0       0    0 => java/lang/InheritableThreadLocal

4     4   0       0    0 => org/eclipse/ui/internal/UISynchronizer$2

2     2   0       0    0 => sun/misc/FloatingDecimal$1

1     1   0       0    0 => org/eclipse/ui/internal/UISynchronizer$1

org/eclipse/core/internal/runtime/ReferenceHashSet$HashableWeakReference =>

35    35   0       0    0 Total

12    12   0       0    0 => org/eclipse/ui/internal/registry/ViewDescriptor

6     6   0       0    0 => org/eclipse/ui/internal/registry/ActionSetDescriptor


com/sun/jmx/mbeanserver/WeakIdentityHashMap$IdentityWeakReference =>

15    15   0       0    0 Total

3     3   0       0    0 => sun/management/MemoryPoolImpl

2     2   0       0    0 => sun/management/GarbageCollectorImpl

1     1   0       0    0 => sun/management/RuntimeImpl


com/sun/java/swing/plaf/windows/DesktopProperty$WeakPCL =>

6     6   0       0    0 Total

4     4   0       0    0 => com/sun/java/swing/plaf/windows/WindowsLookAndFeel$TriggerDesktopProperty

1     1   0       0    0 => com/sun/java/swing/plaf/windows/WindowsLookAndFeel$FontDesktopProperty

1     1   0       0    0 => com/sun/java/swing/plaf/windows/WindowsLookAndFeel$WindowsFontProperty

sun/nio/ch/FileChannelImpl$FileLockReference =>

4     4   0       0    0 Total

4     4   0       0    0 => sun/nio/ch/FileLockImpl

javax/swing/plaf/metal/MetalLookAndFeel$AATextListener =>

1     0   0       1    0 Total

1     0   0       1    0 => null

Phantom References:

2     2   0       0    0 Total for all Phantom References

java/lang/ref/PhantomReference =>

2     2   0       0    0 Total

2     2   0       0    0 => java/lang/Object

Cleared Phantom:

8     8   0       0    0 Total for all Cleared Phantom

jrockit/vm/ObjectMonitor =>

8     8   0       0    0 Total

2     2   0       0    0 => org/eclipse/osgi/framework/eventmgr/EventManager$EventThread

1     1   0       0    0 => org/eclipse/core/internal/jobs/WorkerPool



161   161   0       0    0 Total for all Finalizers

68    68   0       0    0 => java/util/zip/ZipFile

44    44   0       0    0 => java/util/zip/Inflater


Weak Handles:

8311  8311   0       0    0 Total for all Weak Handles

6052  6052   0       0    0 => org/eclipse/osgi/internal/baseadaptor/DefaultClassLoader

1397  1397   0       0    0 => java/lang/String

594   594   0       0    0 => org/eclipse/equinox/launcher/Main$StartupClassLoader


Soft reachable referents not used for at least 201.708 s cleared.

3 SoftReferences was soft alive but not reachable (when found by the GC),

0 was both soft alive and reachable, and 1453 was not soft alive.

----- End of Reference Objects statistics -----

Dark matter: 509525593 bytes

Heap size is not locked

======== END OF HEAPDIAGNOSTIC ===========================

 jrcmd 5176 oom_diagnostics


similar to heap diagnostics

 jrcmd 5176 version



Oracle JRockit(R) build R28.1.0-123-138454-1.6.0_20-20101014-1351-windows-ia32, compiled mode

GC mode: Garbage collection optimized for short pausetimes, strategy: singleconcon

 jrcmd 5176 print_memusage



Total mapped                  1242224KB           (reserved=1074256KB)

-              Java heap      1048576KB           (reserved=1001248KB)

-              GC tables        35084KB

-          Thread stacks        10752KB           (#threads=24)

-          Compiled code         3968KB           (used=3812KB)

-               Internal          968KB

-                     OS        43488KB

-                  Other        70588KB

-        Java class data        27776KB           (malloced=27745KB #32965 in 5906 classes)

- Native memory tracking         1024KB           (malloced=361KB #8)

 jrcmd 5176 print_vmflags




UnlockDiagnosticVMOptions = false (default, writeable)

UnlockInternalVMOptions = false (default)


FailOverToOldVerifier = true (default, writeable)

UseVerifierClassCache = true (default)

UseClassGC = true (default)


UseThreadPriorities = false (default)

DeferThrSuspendLoopCount = 4000 (default, writeable)

SafepointSpinBeforeYield = 2000 (default, writeable)

UseCompilerSafepoints = true (default)

DeferPollingPageLoopCount = -1 (default)

UseMembarForTransitions = false (default)

UseNativeLockProfiling = false (default)


CheckJNICalls = false (default)

AbortOnFailedJNICheck = true (default)

ErrorOnFailedJNICheck = false (default)


UseNewHashFunction = false (default)

TreeMapNodeSize = 64 (default)

MaxDirectMemorySize = 0 (default)

UseLazyStackTraces = true (default)

ShowInternalMethodsInStackTrace = false (default, writeable)


ReduceSignalUsage = false (default)

MaxRecvBufferSize = 65536 (default)

MaxLargePageSize = 0 (default)


UseLowAddressForHeap = true (default)

UseLargePagesForHeap = false (default)

ForceLargePagesForHeap = false (default)

CompressedRefs = false (default)

InitialHeapSize = 0 (default)

MaxHeapSize = 0 (default)

GCTimeRatio = 19 (default)

GCTimePercentage = 0.000000 (default)

GCTrigger = 0 (default)

ForceEarlyOC = true (default)

ForceEarlyOCMaxPercentage = 5.000000 (default)

ForceYCOnLargeAllocationFailed = false (default)

UseNurseryEvacuation = false (default)

DisableEvacuationToNursery = false (default)

SemiRefPostponedPacketSize = 492 (default)

SemiRefPrefetchDistance = 0 (default)

FinalHandleParallelThreshold = 800 (default)

FinalHandlePacketSize = 200 (default)

MaximumNurseryPercentage = 95 (default)

AllowYCDuringOC = true (default)

YcAlignAll = false (default)

YcAlignMaxSpill = 40 (default)

FullSystemGC = false (default)

AllowSystemGC = true (default)

GcCardTableParts = 1024 (default)

GcBalancePrefetchDistance = 4 (default)

GcBalancePacketSize = 493 (default)

NumGenConPrecleaningIterations = 3 (default)

AllowEmergencyParSweep = true (default)

TlaWasteLimit = 2K (set by runtime)

TlaMinSize = 2K (set by runtime)

TlaPreferredSize = 16K (set by runtime)


UseFullCompaction = false (default)

InternalCompactionPercentage = -1.000000 (default)

ExternalCompactionPercentage = -1.000000 (default)

InitialCompactionPercentage = -1.000000 (default)

UseCompaction = true (default)

UseAbortableCompaction = false (default)

NumCompactionHeapParts = 4096 (default)

InitialExternalReservedHeap = 4M (default)

UseFixedExternalReservedHeap = false (default)

MaxCompactionReferences = 0 (default)

MaxCompactionReferencesPerObject = 0 (default)

InternalCompactionParts = -1 (default)

ExternalCompactionParts = -1 (default)

Object allocation:

UseAllocPrefetch = true (default)

RedoAllocPrefetch = true (default)

AllocPrefetchLineLength = 64 (default)

AllocPrefetchDistance = 448 (default)

AllocChunkSize = 512 (default)


UseLockProfiling = false (default)

ThinLockContendedSpinCount = 65 (default)

ThinLockContendedPollCount = 50 (default)

ThinLockConvertToFatThreshold = 240 (default)

FatLockContendedSpinCount = 65 (default)

FatLockContendedPollCount = 50 (default)

MonitorContendedSpinCount = 50 (default)

MonitorContendedPollCount = 20 (default)

UseFatLockDeflation = true (default)

FatLockDeflationThreshold = 50 (default)

UseLockQueueLength = true (default)

UseFatSpin = true (default)

UseAdaptiveFatSpin = false (default)

UseThreadContentionMonitoring = true (default)


UseLazyUnlocking = true (default)

UseLazyUnlockingInJIT = true (default)

UseLazyUnlockingClassBan = true (default)

UseLazyUnlockingTransferClassBan = true (default)


FlightRecorder = true (default)

FlightRecorderOptions = (null) (default)

StartFlightRecording = (null) (default)

Code memory:

CodeBlockAbsorbtionSize = 16 (default)

FreeEmptyCodeBlocks = true (default)

UseLargePagesForCode = false (default)

MaxCodeMemory = 0 (default)

ReserveCodeMemory = false (default)

UseCodeGC = true (default)

CodeGCThreshold = 0 (default)

CodeGCReclaimThreshold = 0 (default)

CodeGCUseReclaim = true (default)

Compiler broker:

MaxOptQueueLength = 0 (default)

OptThreads = 1 (default)

JITThreads = 1 (default)

JITThreadPrio = 5 (default)

OptThreadPrio = 5 (default)

DisableOptsAfter = -1 (default)


PreOpt = false (default)

UseCallProfiling = false (default)

StrictFP = false (default)

CheckStacks = false (default)

DevirtualizeAlways = false (default)

UseStringCache = false (default)

MethodCodeAlignment = 32 (default)

UseInlineObjectAlloc = true (default)

UseOldLockMatching = false (default)


JavaDebug = false (default)


DisableAttachMechanism = false (default)

CrashOnOutOfMemoryError = false (default, writeable)

ExitOnOutOfMemoryError = false (default, writeable)

ExitOnOutOfMemoryErrorExitCode = 51 (default, writeable)

HeapDiagnosticsOnOutOfMemoryError = false (default, writeable)

HeapDiagnosticsPath = (null) (default, writeable)

HeapDumpOnOutOfMemoryError = false (default, writeable)

HeapDumpOnCtrlBreak = false (default)

HeapDumpPath = (null) (default, writeable)

SegmentedHeapDumpThreshold = 2G (default, writeable)

HeapDumpSegmentSize = 1G (default)

StartMemleakOnPort = 0 (default, writeable)

FlightRecordingDumpOnUnhandledException = false (default, writeable)

FlightRecordingDumpPath = (null) (default, writeable)


AbortOnCrash = false (default, writeable)

DumpOnCrash = true (default, writeable)

CoreOnCrash = true (default, writeable)

WaitOnCrash = false (default, writeable)

AbortOnAssert = true (default, writeable)

CrashOnAssert = false (default, writeable)

WaitOnAssert = false (default, writeable)

NumaMemoryPolicy = (null) (default)

BindToNumaNodes = (null) (default)

BindToCPUs = (null) (default)

UseFastTime = true (default)

UseJNIPinning = true (default)

JRockit – a quick view

What is Jrockit JVM?

Is a high performance JVM developed to ensure reliability, scalability, manageability? It’s an enterprise JVM optimized for inter architectures

How machine code is generated by JVM?

Operations stage – JIT compilation – less effective method compilation when the method is called for the first time

Data Structures stage – Thread monitoring – which all methods are frequently called and looking for hot spots

Transformation stage – Code Optimization – recompiles the commonly executed method again efficiently

How threads are used by the JVM?

Each java threads has a stack to store runtime data. -Xss to set the statck size of the thread object for java application, the default for jvm is 256KB

What are the types of Locks?

Thin lock – thread B spins for short time if the lock is acquired by thread A

Fat lock – if thin lock spins for long time, then the CPU time is utilized by other resources by inflating thin lock to fat lock

Recursive lock – synchronized call gets called by itself

Lazy lock – critical section is checked for this lock by the thread

What do you mean by Lock Chains?

Lock chain – A holds lock1 that B also needs, B holds lock 2 that C needs

Open chain – A depends on B, B depends on C and so on. If Long Open chain then the CPU time is wasted in waiting for locks

Deadlock chain – A depends B, B depends on C, C depends on A

Blocked chain – A depends on B, C depends on B, B depends on A

How memory is managed by JVM?

Most common assumption is that an object is most likely to die shortly after it was created: called infant mortality. Objects that are referenced are called as live objects .The process of finding and freeing the space used by these objects are called as Garbage collections

Heap contains two generations. [Nursery or Young] and Old Spaces

TLA [Thread local Area] – free memory chunks from the heap for java threads for exclusive use

Nursery/young’s space – new objects are allocated here – Eden space. Nursery has kept area for current object allocation before young’s collection

Survivor space – objects survived GC of Eden space

Tenured space – objects existed sometime in survivor space are moved to tenured or old space

Old space – after young’s collection objects are moved here

Perm Space – Area of the VM that is used to store the data structures and class information’s.

-XX:MaxPermSize is used to get rid of outofmemoryerror

While promotion if the memory is less than they are stored within young’s space called fragmented nursery – promotion failure

Fragmentation – when the memory is freed the free space may appear in small chunks in many area so that there might not be a contiguous area for allocation of large objects

Compaction – compressing the live objects together and completely reclaiming the memory

What are the basic GC algorithms?

Reference Counting

Mark and Sweep



What are different types of collections?

Serial collection – only one CPU is used for GC, -XX:+UseSerialGC

Parallel Collection – GC is split between different CPU and executed simultaneously, -XX:+UseParallelGC

Stop the world collection – the entire application is completely suspended during the collection

Concurrent collection – one or more GC tasks are done concurrently with few stop the world pauses

Compacting collection – this will compact the entire free space by compressing the live objects

Non compacting collection – will not compact leads to fragmentation

Copying collection – copies the live objects to different area

Parallel Compacting Collection – -XX: +UseParallelOldGC

What are the collectors used?

What are all the performance metrics?

Throughput – % of time not spent in GC

GC overhead – % of time spent in GC

Pause time – unresponsive because of GC

Frequency of collection – how often GC is performed

Memory Footprints – measure of heap size

Promptness – the time between objects GC and memory becomes available

CPU usages – CPU usage in GC

What are the tools to evaluate GC performance?






What is Basic GC tuning?

Throughput goal – -XX:GCTimeRatio, total time to be spent on GC

Maximum Pause Time Goal – -XX:MaxGCPauseMillis, indication for collector for pause time

-XX:ParallelGCThreads – number of CPU

Footprint goal

What are Advance GC Tuning?

-Xms – starting heap size

Xmx – maximum heap size

-XX:MinHeapFreeRatio – 40 – proportion of free space to expand

-XX:MaxHeapFreeRatio – 70 – proportion of free space to shrink

-XX:NewSize – intial size of new young generation [eden + survivor 1 + survivor 2]

-XX:MaxNewSize – maximum young size

-XX:NewRatio – ratio between young and tenured size[old]

-XX:SurvivorRatio – ratio between each survivor and eden

-XX:TargetSurvivorRatio – ratio between each survivor and eden after GC

-XX:Permsize – starting permanent generation

-XX:MaxPermSize – max size of permanent generation

-XX:+DisableExplicitGC – disable System.gc()

-XX:+ScavengeBeforeFullGC – perform minor before major collection

-XX:+UseGCOverheadLimit – if 98% of CPU time is spent on GC, then throws OutOfMemoryError

Thoughts on Java that works

Disclaimer: This is just to get an idea of the implementation, please do not copy the source code

The problem reads like

Basic sales tax is applicable at a rate of 10% on all goods, except books,
food, and medical products that are exempt. Import duty is an additional
sales tax applicable on all imported goods at a rate of 5%, with no
When I purchase items I receive a receipt which lists the name of all the
items and their price (including tax), finishing with the total cost of the
items, and the total amounts of sales taxes paid.  The rounding rules for
sales tax are that for a tax rate of n%, a shelf price of p contains
(np/100 rounded up to the nearest 0.05) amount of sales tax.
Write an application that prints out the receipt details for these shopping

Find the complete solved solution here

A squad of robotic rovers are to be landed by NASA on a plateau on Mars.
This plateau, which is curiously rectangular, must be navigated by the
rovers so that their on-board cameras can get a complete view of the
surrounding terrain to send back to Earth.

A rover’s position and location is represented by a combination of x and y
co-ordinates and a letter representing one of the four cardinal compass
points. The plateau is divided up into a grid to simplify navigation. An
example position might be 0, 0, N, which means the rover is in the bottom
left corner and facing North.

In order to control a rover, NASA sends a simple string of letters. The
possible letters are ‘L’, ‘R’ and ‘M’. ‘L’ and ‘R’ makes the rover spin 90
degrees left or right respectively, without moving from its current spot.
‘M’ means move forward one grid point, and maintain the same heading.

Assume that the square directly North from (x, y) is (x, y+1).

Find the complete solved solution here

Learn it from JSR

References for core and detail knowledge of technologies related to Java

JSR – http://jcp.org/en/jsr/platform

Java – http://java.sun.com/docs/books/jls/third_edition/html/j3TOC.html

J2EE5 – http://download.oracle.com/docs/cd/E17477_01/javaee/5/tutorial/doc/docinfo.html

JVM – http://java.sun.com/docs/books/jvms/second_edition/html/VMSpecTOC.doc.html

JSP – http://jcp.org/aboutJava/communityprocess/final/jsr152/index.html

JSF – http://jcp.org/aboutJava/communityprocess/final/jsr252/index.html

EJB2 – http://jcp.org/aboutJava/communityprocess/final/jsr019/index.html

EJB3 – http://jcp.org/aboutJava/communityprocess/final/jsr220/index.html

EJB3.1 – http://jcp.org/aboutJava/communityprocess/final/jsr318/index.html

JSTL – http://jcp.org/aboutJava/communityprocess/final/jsr052/index.html

Servlets – http://jcp.org/aboutJava/communityprocess/final/jsr053/index.html

JDBC  – http://jcp.org/aboutJava/communityprocess/final/jsr054/index.html

Web services – http://jcp.org/aboutJava/communityprocess/final/jsr109/index.html