Java BuzzWords - 11

Dynamic

In a number of ways, Java is a more dynamic language than C or C++. It was designed to adapt to an evolving environment. For example, one major problem with C++ in a production environment is a side-effect of the way that code is implemented. If company A produces a class library (a library of plug and play components) and company B buys it and uses it in their product, then if A changes its library and distributes a new release, B will almost certainly have to recompile and redistribute their own software. In an environment where the end user gets A and B's software independently (say A is an OS vendor and B is an application vendor) problems can result.

For example, if A distributes an upgrade to its libraries, then all of the software from B will break. It is possible to avoid this problem in C++, but it is extraordinarily difficult and it effectively means not using any of the language's OO features directly.

By making these interconnections between modules later, Java completely avoids these problems and makes the use of the object-oriented paradigm much more straightforward. Libraries can freely add new methods and instance variables without any effect on their clients.

An interface specifies a set of methods that an object can perform but leaves open how the object should implement those methods. A class implements an interface by implementing all the methods contained in the interface. In contrast, inheritance by subclassing passes both a set of methods and their implementations from superclass to subclass. A Java class can implement multiple interfaces but can only inherit from a single superclass. Interfaces promote flexibility and reusability in code by connecting objects in terms of what they can do rather than how they do it.

Classes have a runtime representation: there is a class named Class, instances of which contain runtime class definitions. If, in a C or C++ program, you have a pointer to an object but you don't know what type of object it is, there is no way to find out. However, in Java, finding out based on the runtime type information is straightforward. Because casts are checked at both compile-time and runtime, you can trust a cast in Java. On the other hand, in C and C++, the compiler just trusts that you're doing the right thing.It is also possible to look up the definition of a class given a string containing its name. This means that you can compute a data type name and have it easily dynamically-linked into the running system.