Java Programming

James Gosling, Mike Sheridan, and Patrick Naughton initiated the Java language project in June 1991. Java was originally designed for interactive television, but it was too advanced for the digital cable television industry at the time. The language was initially called Oak after an oak tree that stood outside Gosling's office; it went by the name Green later, and was later renamed Java, from Java coffee, said to be consumed in large quantities by the language's creators. Gosling aimed to implement avirtual machine and a language that had a familiar C/C++ style of notation.

Sun Microsystems released the first public implementation as Java 1.0 in 1995. It promised "Write Once, Run Anywhere" (WORA), providing no-cost run-times on popularplatforms. Fairly secure and featuring configurable security, it allowed network- and file-access restrictions. Major web browsers soon incorporated the ability to run Java applets within web pages, and Java quickly became popular. With the advent of Java 2 (released initially as J2SE 1.2 in December 1998-1999), new versions had multiple configurations built for different types of platforms. For example, J2EE targeted enterprise applications and the greatly stripped-down version J2ME for mobile applications (Mobile Java). J2SE designated the Standard Edition. In 2006, for marketing purposes, Sun renamed new J2 versions as Java EE, Java ME, and Java SE, respectively.

In 1997, Sun Microsystems approached the ISO/IEC JTC1 standards body and later the Ecma International to formalize Java, but it soon withdrew from the process. Java remains a de factostandard, controlled through the Java Community Process. At one time, Sun made most of its Java implementations available without charge, despite their proprietary software status. Sun generated revenue from Java through the selling of licenses for specialized products such as the Java Enterprise System. Sun distinguishes between its Software Development Kit (SDK) and Runtime Environment (JRE) (a subset of the SDK); the primary distinction involves the JRE's lack of the compiler, utility programs, and header files.

On November 13, 2006, Sun released much of Java as free and open source software, (FOSS), under the terms of the GNU General Public License (GPL). On May 8, 2007, Sun finished the process, making all of Java's core code available under free software/open-source distribution terms, aside from a small portion of code to which Sun did not hold the copyright.

Sun's vice-president Rich Green said that Sun's ideal role with regards to Java was as an "evangelist." Following Oracle Corporation's acquisition of Sun Microsystems in 2009-2010, Oracle has described itself as the "steward of Java technology with a relentless commitment to fostering a community of participation and transparency". This did not hold Oracle, however, from filing a lawsuit against Google shortly after that for using Java inside the Android SDK (see Google section below). Java software runs on laptops to data centers, game consoles to scientific supercomputers. There are 930 million Java Runtime Environment downloads each year and 3 billion mobile phones run Java.[21] On April 2, 2010, James Gosling resigned from Oracle.

By default, operator new() allocates memory on the free store (the heap). The standard defines four global operators:

The global operator new() has three standard implementations defined in :

1. void* operator new (std::size_t size);
2. void* operator new (std::size_t size, const std::nothrow_t& nothrow_value) noexcept;
3. void* operator new (std::size_t size, void* ptr) noexcept;

The first implementation allocates size bytes on the free store and returns a generic pointer (void*) to the first byte of the allocation. If the allocation fails for any reason, a std::bad_alloc exception is thrown. This operator is therefore known as a throwing allocation.

The second is the same as the first but does not throw an exception. If the allocation fails for any reason, nullptr is returned instead. this is known as a nothrow allocation.

The third version is used when (raw) memory has already been allocated and simply returns the given ptr argument. The memory referred to by ptr need not be allocated on the heap. This version is known as placement.

In all three cases, the allocated memory is simply raw, uninitialised memory (similar to what we would expect when invoking the standard global malloc() function in C).

In addition, the standard also defines global operator new[]() (also in ):

1. void* operator new[] (std::size_t size);
2. void* operator new[] (std::size_t size, const std::nothrow_t& nothrow_value) noexcept;
3. void* operator new[] (std::size_t size, void* ptr) noexcept;

These versions are used when we wish to allocate an array of objects and have similar behaviours to the "normal" global operators.

Note that all these operators are defined implicitly; we do not need to explicitly include the header to use them.

In order to physically construct an object via global operator new (), the object's class must define a static member operator new (). Given that it would be tedious to do this for every class that we define, this is done implicitly for us. Thus when we invoke the following:

T* ptr = new T {args...};

T* ptr = new T[N] {args...};

we are actually invoking the following:

T* ptr = T::operator new (args...);

T* ptr = T::operator new[] (N, args...);

The (implicit) static member operator new() and operator new[]() are implementation-defined, but will generally be defined as follows:

T* T::operator new (args...) {

T* ptr = ::new (sizeof (T)); // invoke the global operator (may throw)

// initialise the memory from args...

return ptr;

}

T* T::operator new[] (std::size_t N, args...) {

T* ptr = ::new[] (N * sizeof (T)); // invoke the global operator (may throw)

// initialise the memory for each N from args...

return ptr;

}

Now we can see where the std::size_t argument passed to global operator new() actually comes from.

Given that T::operator new() is a member function, it can be overloaded on a class-by-class basis if we wish to provide our own memory management facility. We can also overload the global operator new(), however this is not recommended because there's no way of knowing how other classes we have no control over might be affected, particularly those which provide their own member operator new() overloads and which expect the default behaviour of the global operator new(). Overloading global operator new() is not for the feint-hearted, thus it is recommended you use a tried-and-tested library for global memory management rather than attempting to write your own from scratch.

A number of well-tested open-source Matrix Java libraries are available. Best to find and use one that's been around for a while since most of the bugs have been worked out. If you need to write your own it's still worth-while to examine the APIs of those libraries first.

JAMA is a free Java library for basic linear algebra and matrix operations developed as a straightforward public-domain reference implementation by MathWorks and NIST.

Example of Use. The following simple example solves a 3x3 linear system Ax=b and computes the norm of the residual.

double[][] array = {{1.,2.,3},{4.,5.,6.},{7.,8.,10.}};

Matrix A = new Matrix(array);

Matrix b = Matrix.random(3,1);

Matrix x = A.solve(b);

Matrix Residual = A.times(x).minus(b);

double rnorm = Residual.normInf();

Java allows us to perform 'dynamic initialization' of variables too.

What this means is that you can initialize variables using expressions (as will be seen in the example).

In the program, we have a int variable 'root' which has an initial defined value of 10. We then create another variable 'square' of the same data-type, which will store the square of root.

//This program displays dynamic initialization in java

publicclassExample

{

publicstaticvoidmain(String args[])

{

introot=10; //root has a constant value assigned

intsquare=root*root; //notice that square has "root*root" assigned to it

//if u change the value of root,

//the value of square changes accordingly

//after each compilation

//display the values of square and root

System.out.println("Root= " +root + " Square= "+square);

}

}

Oracle owns Java.

Previous owner was Sun micro systems.

Hibernate is an object-relational mapping (ORM) library for the Java language, providing a framework for mapping an object-oriented domain model to a traditional relational database. Hibernate solves object-relational impedance mismatch problems by replacing direct persistence-related database accesses with high-level object handling functions.

Hibernate is free as open source software that is distributed under the GNU Lesser General Public License.

Rather than utilize bytecode processing or code generation, Hibernate uses runtime reflection to

determine the persistent properties of a class. The objects to be persisted are defined in a

mapping document, which serves to describe the persistent fields and associations, as well as any

subclasses or proxies of the persistent object. The mapping documents are compiled at

application startup time and provide the framework with necessary information for a class.

Additionally, they are used in support operations, such as generating the database schema or

creating stub Java source files.

Hibernate's primary feature is mapping from Java classes to database tables (and from Java data types to SQL data types). Hibernate also provides data query and retrieval facilities. Hibernate generates the SQL calls and relieves the developer from manual result set handling and object conversion, keeping the application portable to all supported SQL databases, with database portability delivered at very little performance overhead.

Facilities to arrange one-to-many and many-to-many relationships between classes are provided. In addition to managing association between objects, Hibernate can also manage reflexive associations where an object has a one-to-many relationship with other instances of its own type.

Hibernate supports the mapping of custom value types. This makes the following scenarios possible:

• Overriding the default SQL type that Hibernate chooses when mapping a column to a property
• Mapping Java Enum to columns as if they were regular properties
• Mapping a single property to multiple columns

Collections of data objects are typically stored in Java collection objects such as Set and List. Java Generics can be used in Java 5 and higher. Hibernate can be configured to lazy load associated collections. Lazy loading is the default as of Hibernate 3.

Related objects can be configured to cascade operations from one to the other. For example, a parent such as an Album object can be configured to cascade its save and/or delete operation to its child Track objects. This can reduce development time and ensure referential integrity. A dirty checkingfeature avoids unnecessary database write actions by performing SQL updates only on the modified fields of persistent objects.