JAVA / JDK Version History

Java Version History

JDK 1.0 (january 23, 1996) oak
– Initial release

JDK 1.1 (february 19, 1997)
– Retooling of the AWT event model
– Inner classes added to the language
– JavaBeans
– JDBC
– RMI

J2SE 1.2 (December 8, 1998) playground
This and subsequent releases through J2SE 5.0 were rebranded retrospectively Java 2 & version name “J2SE”
(Java 2 platform, Standard edition) replaced JDK to distinguish the base platform from
J2EE (java 2 platform, enterprise edition) and J2ME (java 2 platform, micro edition).

– Strictfp keyword
– Reflection
– Swing api integration into the core classes
– JVM equipped with a jit compiler
– Java plug-in
– Java IDL
– An IDL implementation for corba interoperability
– Collections Framework

J2SE 1.3 (may 8, 2000) kestrel
– Hotspot jvm included
– JavaSound
– JNDI included in core libraries
– Java platform debugger architecture (jpda)
– RMI was modified to support optional compatibility with corba

J2SE 1.4 (february 6, 2002) merlin
– assert keyword
– Regular expressions
– Exception chaining (allows an exception to encapsulate original lower-level exception)
– Internet protocol version 6 (IPV6) support
– Non-blocking nio (new input/output)
– Logging API
– Image i/o api for reading and writing images in formats like jpeg and png
– Integrated XML parser and XSLT processor (JAXP)
– Integrated security and cryptography extensions (JCE, JSSE, JAAS)
– Java web start

J2SE 5.0 (september 30, 2004) tiger [originally numbered 1.5]
– Generics: provides compile-time (static) type safety for collections and eliminates the need for most typecasts (type conversion).
– Metadata: also called annotations; allows language constructs such as classes and methods to be tagged with additional data, which can then be processed by metadata-aware utilities.
– Autoboxing/unboxing: automatic conversions between primitive types (such as int) and primitive wrapper classes (such as integer).
– Enumerations: the enum keyword creates a typesafe, ordered list of values (such as day.monday, day.tuesday, etc.). Previously this could only be achieved by non-typesafe constant integers or manually constructed classes (typesafe enum pattern).
– Swing: new skinnable look and feel, called synth.
– Var args: the last parameter of a method can now be declared using a type name followed by three dots (e.g. Void drawtext(string… Lines)). In the calling code any number of parameters of that type can be used and they are then placed in an array to be passed to the method, or alternatively the calling code can pass an array of that type.
– Enhanced for each loop: the for loop syntax is extended with special syntax for iterating over each member of either an array or any iterable, such as the standard collection classesfix the previously broken semantics of the java memory model, which defines how threads interact through memory.
– Automatic stub generation for rmi objects.
– Static imports concurrency utilities in package java.util.concurrent.
– Scanner class for parsing data from various input streams and buffers.
– Assertions
– StringBuilder class (in java.lang package)
– Annotations

Java SE 6 (december 11, 2006) mustang
sun replaced the name “J2SE” with java se and dropped the “.0” from the version number.
Beta versions were released in february and june 2006, leading up to a final release that occurred on december 11, 2006.
The current revision is update 14 which was released in may 2009.

– Support for older win9x versions dropped.
– Scripting lang support: Generic API for integration with scripting languages, & built-in mozilla javascript rhino integration
– Dramatic performance improvements for the core platform, and swing.
– Improved web service support through JAX-WS JDBC 4.0 support
– Java compiler API: an API allowing a java program to select and invoke a java compiler programmatically.
– Upgrade of JAXB to version 2.0: including integration of a stax parser.
– Support for pluggable annotations
– Many GUI improvements, such as integration of swingworker in the API, table sorting and filtering, and true swing double-buffering (eliminating the gray-area effect).

Java se 6 update 10
A major enhancement in terms of end-user usability.
– Java Deployment Toolkit, a set of javascript functions to ease the deployment of applets and java web start applications.
– Java Kernel, a small installer including only the most commonly used jre classes. Enhanced updater.
– Enhanced versioning and pack200 support: server-side support is no longer required.
– Java quick starter, to improve cold start-up time.
– Improved performance of java2D graphics primitives on windows, using direct3D and hardware acceleration.
– A new Swing look and feel called NIMBUS and based on synth.
– Next-generation java plug-in: applets now run in a separate process and support many features of web start applications.

Java se 6 update 12
This release includes the highly anticipated 64-bit java plug-in (for 64-bit browsers only), windows server 2008 support,
and performance improvements of java and JAVAFX applications.

 

Java SE 7

  • Swing
  • IO and New IO
  • Networking
  • Security
  • Concurrency Utilities
  • Rich Internet Applications (RIA)/Deployment
    • Requesting and Customizing Applet Decoration in Dragg able Applets
    • Embedding JNLP File in Applet Tag
    • Deploying without Codebase
    • Handling Applet Initialization Status with Event Handlers
  • Java 2D
  • Java XML – JAXP, JAXB, and JAX-WS
  • Internationalization
  • java.lang Package
    • Multithreaded Custom Class Loaders in Java SE 7
  • Java Programming Language
    • Binary Literals
    • Strings in switch Statements
    • The try-with-resources Statement
    • Catching Multiple Exception Types and Rethrowing Exceptions with Improved Type Checking
    • Underscores in Numeric Literals
    • Type Inference for Generic Instance Creation
    • Improved Compiler Warnings and Errors When Using Non-Reifiable Formal Parameters with Varargs Methods
  • Java Virtual Machine (JVM)
    • Java Virtual Machine Support for Non-Java Languages
    • Garbage-First Collector
    • Java HotSpot Virtual Machine Performance Enhancements
  • JDBC

 

 

Difference Between Stack and Heap

What Is Stack?

Each Java virtual machine thread has a private Java virtual machine stack, created at the same time as the thread. A Java virtual machine stack stores frames. It holds local variables and partial results, and plays a part in method invocation and return. Because the Java virtual machine stack is never manipulated directly except to push and pop frames, frames may be heap allocated. The memory for a Java virtual machine stack does not need to be contiguous.

The Java virtual machine specification permits Java virtual machine stacks either to be of a fixed size or to dynamically expand and contract as required by the computation. If the Java virtual machine stacks are of a fixed size, the size of each Java virtual machine stack may be chosen independently when that stack is created. A Java virtual machine implementation may provide the programmer or the user control over the initial size of Java virtual machine stacks, as well as, in the case of dynamically expanding or contracting Java virtual machine stacks, control over the maximum and minimum sizes.

The following exceptional conditions are associated with Java virtual machine stacks:

  • If the computation in a thread requires a larger Java virtual machine stack than is permitted, the Java virtual machine throws a StackOverflowError.
  • If Java virtual machine stacks can be dynamically expanded, and expansion is attempted but insufficient memory can be made available to effect the expansion, or if insufficient memory can be made available to create the initial Java virtual machine stack for a new thread, the Java virtual machine throws an OutOfMemoryError

The Stack section of memory contains methods, local variables and reference variables.

What Is Heap?

The Java virtual machine has a heap that is shared among all Java virtual machine threads. The heap is the runtime data area from which memory for all class instances and arrays is allocated.

The heap is created on virtual machine start-up. Heap storage for objects is reclaimed by an automatic storage management system (known as a garbage collector); objects are never explicitly deallocated. The Java virtual machine assumes no particular type of automatic storage management system, and the storage management technique may be chosen according to the implementor’s system requirements. The heap may be of a fixed size or may be expanded as required by the computation and may be contracted if a larger heap becomes unnecessary. The memory for the heap does not need to be contiguous.

The heap mainly store objects create using or class level variables.

The following exceptional condition is associated with the heap:

  • If a computation requires more heap than can be made available by the automatic storage management system, the Java virtual machine throws an OutOfMemoryError

The Heap section contains Objects (may also contain reference variables).

Points to Remember:

  • When a method is called , a frame is created on the top of stack.
  • Once a method has completed execution , flow of control returns to the calling method and its corresponding stack frame is flushed.
  • Local variables are created in the stack
  • Instance variables are created in the heap & are part of the object they belong to.
  • Reference variables are created in the stack.

What if Object has a reference as its instance variable?


public static void main(String args[]){

A parent = new A();
//more code

}

class A{

B child = new B();
int e;
//more code

}

class B{

int c;
int d;
//more code

}

In this case , the reference variable “child” will be created in heap ,which in turn will be pointing to its object, something like the diagram shown below.

Get Nth highest record from table

Hello friends,

Recently in one interview i had question for get 3rd highest amount  record from table ,

i had make query with sub-query , but interviewer had something different in mind and told me any another option, so here i will  post some of the option to get nth highest record…

1) select * from (select year,amount,row_number() over (order by amount desc) rn from budget) where rn = 3;

2) SELECT *  FROM budget A WHERE &N = (SELECT COUNT (DISTINCT (b.amount)) FROM budget B WHERE a.amount<=b.amount);

here we have to give value N = 3

3)select amount from (select amount from (select distinct amount from ( select distinct amount from budget order by amount desc) where rownum<=3) order by amount asc) where rownum<=1;

4) select amount from (select rownum r1,amount from (select distinct(amount) from budget where amount is NOT NULL order by amount desc)) where  r1 = 3;

5) SELECT LEVEL,MAX(amount) FROM budget WHERE LEVEL IN (3) CONNECT BY PRIOR amount > amount GROUP BY LEVEL;

here, interestingly we can get 2nd and 3rd most highest amount record also…

SELECT LEVEL,MAX(amount) FROM budget WHERE LEVEL IN (2,3) CONNECT BY PRIOR amount > amount GROUP BY LEVEL;

 

I had find this much , you have to try for more option and if you will get it then please post in comments.

Cheers….  🙂

Struts 1.x Vs Struts 2.x

Struts 2.x is very simple as compared to struts 1.x, few of its excelent features are:

1. Servlet Dependency:

Actions in Struts1 have dependencies on the servlet API since the HttpServletRequest and HttpServletResponse objects are passed to the execute method when an Action is invoked but in case of Struts 2, Actions are not container dependent because they are made simple POJOs. In struts 2, the servlet contexts are represented as simple Maps which allows actions to be tested in isolation. Struts 2 Actions can access the original request and response, if required. However, other architectural elements reduce or eliminate the need to access the HttpServetRequest or HttpServletResponse directly.

2. Action classes

Programming the abstract classes instead of interfaces is one of design issues of struts1 framework that has been resolved in the struts 2 framework.
Struts1 Action classes needs to extend framework dependent abstract base class. But in case of Struts 2 Action class may or may not implement interfaces to enable optional and custom services. In case of Struts 2 , Actions are not container dependent because they are made simple POJOs. Struts 2 provides a base ActionSupport class to implement commonly used interfaces. Albeit, the Action interface is not required. Any POJO object with an execute signature can be used as an Struts 2 Action object.

3. Validation

Struts1 and Struts 2 both supports the manual validation via a validate method.
Struts1 uses validate method on the ActionForm, or validates through an extension to the Commons Validator. However, Struts 2 supports manual validation via the validate method and the XWork Validation framework. The Xwork Validation Framework supports chaining validation into sub-properties using the validations defined for the properties class type and the validation context.

4. Threading Model

In Struts1, Action resources must be thread-safe or synchronized. So Actions are singletons and thread-safe, there should only be one instance of a class to handle all requests for that Action. The singleton strategy places restrictions on what can be done with Struts1 Actions and requires extra care to develop. However in case of Struts 2, Action objects are instantiated for each request, so there are no thread-safety issues. (In practice, servlet containers generate many throw-away objects per request, and one more object does not impose a performance penalty or impact garbage collection.)

5. Testability

Testing Struts1 applications are a bit complex. A major hurdle to test Struts1 Actions is that the execute method because it exposes the Servlet API. A third-party extension, Struts TestCase, offers a set of mock object for Struts1. But the Struts 2 Actions can be tested by instantiating the Action, setting properties and invoking methods. Dependency Injection support also makes testing simpler. Actions in struts2 are simple POJOs and are framework independent, hence testability is quite easy in struts2.

6. Harvesting Input

Struts1 uses an ActionForm object to capture input. And all ActionForms needs to extend a framework dependent base class. JavaBeans cannot be used as ActionForms, so the developers have to create redundant classes to capture input.
However Struts 2 uses Action properties (as input properties independent of underlying framework) that eliminates the need for a second input object, hence reduces redundancy. Additionally in struts2, Action properties can be accessed from the web page via the taglibs. Struts 2 also supports the ActionForm pattern, as well as POJO form objects and POJO Actions. Even rich object types, including business or domain objects, can be used as input/output objects.

7. Expression Language

Struts1 integrates with JSTL, so it uses the JSTL-EL. The struts1 EL has basic object graph traversal, but relatively weak collection and indexed property support. Struts 2 can also use JSTL, however it supports a more powerful and flexible expression language called “Object Graph Notation Language” (OGNL).

8. Binding values into views

In the view section, Struts1 uses the standard JSP mechanism to bind objects (processed from the model section) into the page context to access. However Struts 2 uses a “ValueStack” technology so that the taglibs can access values without coupling your view to the object type it is rendering. The ValueStack strategy allows the reuse of views across a range of types which may have the same property name but different property types.

9. Type Conversion

Usually, Struts1 ActionForm properties are all Strings. Struts1 uses Commons-Beanutils for type conversion. These type converters are per-class and not configurable per instance. However Struts 2 uses OGNL for type conversion. The framework includes converters for basic and common object types and primitives.

10. Control Of Action Execution

Struts1 supports separate Request Processor (lifecycles) for each module, but all the Actions in a module must share the same lifecycle. However Struts 2 supports creating different lifecycles on a per Action basis via Interceptor Stacks. Custom stacks can be created and used with different Actions as needed.

Spring vs Struts 2.0

While creating J2EE applications, it needs to be decided some times which technology we should go for – Struts or Spring. This is some points comparison between Spring and Struts.

1. In most of the key features compared, Spring MVC and Struts 2 are equally good, except in the UI supports. It seems to me Spring MVC just provides tags for basic HTML form tags while Struts/WebWork 2 provides many out-of-box JSF-styled complex and composite tags, such as:
a) Struts 2 integrates with Dojo AJAX framework closely and provides many complex UI components out-of-box, such as datepicker, tooltips, etc.
b) Struts 2 has AJAX theme.
c) Struts 2 tags are stylesheet-driven, making it easier to develop consistent pages.
d) Struts 2 checkboxes are stateful, and require no special handling.
The recent release of Spring 2.0 does not seem to have any work on this area.

2. Struts is mainly a presentation layer framework, like redirecting to a particular page ,doing client side validations etc which otherwise very tedious using jsp and servlets. Spring is a complete J2EE framework having seven independent layers which can be used all together or few layers integrated with some other framework. Spring provides declarative transaction management and AOP. One layer of spring is for presentation purpose like struts but for only presentation layer, struts is better than spring.

3. Struts has been around a long time and has been popular for years – there’s a wealth of knowledge about it in the user community and more literature around

4. If you want a bunch of taglibs that generate form fields and so forth, Struts is probably the better choice.

5. Our UI is mostly click-driven and light on data and validation. It seems to me that most people run into difficulties with Struts when they start moving a lot of data from HTTP into the model. We didn?t have that problem .

6. Spring does not present a framework for implementing business/domain logic. It helps you create a Controller and a View for your application, no Model though. Spring is a fully fledged application framework, that has a large stack of sub projects.

7. As for spring, if we look at its history, it started as an effort for supplying a solution for enterprise java applications, and to replace EJBs (while it also provided integration with EJBs for people who didn’t want to ditch that). Spring is much more than an MVC framework. It provides dependency injection, AOP, integration with almost every known framework, a security framework (a separate sub-project), and a lot of other stuff. Struts 2 and hibernate integrate easily with spring, so you might like to add it to your stack, without ditching struts 2
8. If you’re going to use Spring for other middleware services, and you have no Struts expertise in house, then it would be simplest to go with SpringMVC. If you know Struts well or have team members who do, or you already have a Struts project, it may make sense to stick with it.

So, basically, it depends on the requirements and the resources what and how you want to achieve which will decide what is to be used, Stuts 2.0 or Spring.

HashMap vs Hashtable vs HashSet

I was reading about collection framework of Java. And was studying Hashtable, HashMap and HashSet. Its quite interesting to know the differences between them. In this post I will discuss these three with examples.

Hashtable

Hashtable is basically a datastructure to retain values of key-value pair.

  • It didn’t allow null for both key and value. You will get NullPointerException if you add null value.
  • It is synchronized. So it comes with its cost. Only one thread can access in one time
Hashtable<Integer,String>; cityTable = new Hashtable<Integer,String>();
cityTable.put(1, "Lahore");
cityTable.put(2, "Karachi");
cityTable.put(3, null); /* NullPointerEcxeption at runtime*/

System.out.println(cityTable.get(1));
System.out.println(cityTable.get(2));
System.out.println(cityTable.get(3));

HashMap

Like Hashtable it also accepts key value pair.

  • It allows null for both key and value
  • It is unsynchronized. So come up with better performance
HashMap<Integer,String> productMap = new HashMap<Integer,String>();
productMap.put(1, "Keys");
productMap.put(2, null);

HashSet

HashSet does not allow duplicate values. It provides add method rather put method. You also use its contain method to check whether the object is already available in HashSet. HashSet can be used where you want to maintain a unique list.

HashSet<String> stateSet = new HashSet<String>();
stateSet.add ("CA");
stateSet.add ("WI");
stateSet.add ("NY");

if (stateSet.contains("PB")) /* if CA, it will not add but shows following message*/
System.out.println("Already found");
else
stateSet.add("PB");

Vector or ArrayList — which is better?

 Vector or ArrayList — which is better and why?

Sometimes Vector is better; sometimes ArrayListis better; sometimes you don’t want to use either. I hope you weren’t looking for an easy answer because the answer depends upon what you are doing. There are four factors to consider:

  • API
  • Synchronization
  • Data growth
  • Usage patterns

Let’s explore each in turn.

API

In The Java Programming Language (Addison-Wesley, June 2000) Ken Arnold, James Gosling, and David Holmes describe the Vector as an analog to the ArrayList. So, from an API perspective, the two classes are very similar. However, there are still some major differences between the two classes.

Synchronization

Vectors are synchronized. Any method that touches the Vector‘s contents is thread safe. ArrayList, on the other hand, is unsynchronized, making them, therefore, not thread safe. With that difference in mind, using synchronization will incur a performance hit. So if you don’t need a thread-safe collection, use the ArrayList. Why pay the price of synchronization unnecessarily?

Data growth

Internally, both the ArrayList and Vector hold onto their contents using an Array. You need to keep this fact in mind while using either in your programs. When you insert an element into an ArrayList or a Vector, the object will need to expand its internal array if it runs out of room. A Vector defaults to doubling the size of its array, while the ArrayList increases its array size by 50 percent. Depending on how you use these classes, you could end up taking a large performance hit while adding new elements. It’s always best to set the object’s initial capacity to the largest capacity that your program will need. By carefully setting the capacity, you can avoid paying the penalty needed to resize the internal array later. If you don’t know how much data you’ll have, but you do know the rate at which it grows, Vector does possess a slight advantage since you can set the increment value.

Usage patterns

Both the ArrayList and Vector are good for retrieving elements from a specific position in the container or for adding and removing elements from the end of the container. All of these operations can be performed in constant time — O(1). However, adding and removing elements from any other position proves more expensive — linear to be exact: O(n-i), where n is the number of elements and i is the index of the element added or removed. These operations are more expensive because you have to shift all elements at index i and higher over by one element. So what does this all mean?

It means that if you want to index elements or add and remove elements at the end of the array, use either a Vector or an ArrayList. If you want to do anything else to the contents, go find yourself another container class. For example, the LinkedList can add or remove an element at any position in constant time — O(1). However, indexing an element is a bit slower — O(i) where i is the index of the element. Traversing an ArrayList is also easier since you can simply use an index instead of having to create an iterator. The LinkedList also creates an internal object for each element inserted. So you have to be aware of the extra garbage being created.

Finally, in “PRAXIS 41” from Practical Java (Addison-Wesley, Feb. 2000) Peter Haggar suggests that you use a plain old array in place of either Vector or ArrayList — especially for performance-critical code. By using an array you can avoid synchronization, extra method calls, and suboptimal resizing. You just pay the cost of extra development time.