Which is the primary need to develop Java programming from C plus plus?

Answer 1

The primary need to convert any language source, including C++, to Java is simply one of portability.

While C++ is itself portable, writing cross-platform code requires that you write code in a more abstract manner than you would when writing for a specific platform, making extensive use of compiler directives to determine which version of each translation unit will be compiled upon which particular platform. This increases code maintenance because you must then maintain separate versions of the platform-specific code, as well as include a different set of headers for each platform, and thus call different functions for each platform. You must also compile the source separately upon each supported platform, which means the code must be as generic as possible in order to be understood by every possible compiler. Thus cross-platform C++ code tends to be limited to the most popular platforms only, which usually means Windows and Unix only.

Java's higher level of abstraction is such that you need only write one set of instructions and compile it one time only. The Java virtual machine handles all the low-level machine specifics, so the same executable will run on any machine that has a Java virtual machine implementation. While this greatly reduces code maintenance and increases portability, the need to interpret the compiled byte code (rather than native machine code which requires no interpretation) reduces performance enormously. Thus the ease of maintenance has to be weighed against the loss of performance to determine if it is a worthwhile exercise.