What kinds of differences are compiling and running Java vs C programs?

Answer 1

Although Java is often described as a compiled language, it is a language that is both compiled and interpreted. Unlike C++ which typically compiles to native machine code, Java compiles to Java byte code, the native language of the Java virtual machine. The key difference here is that the Java virtual machine is not machine dependent, thus the same byte code can be executed upon any physical machine with a suitable Java virtual machine implementation; it is highly portable. Machine code can only be executed upon the machine architecture for which it was compiled. To support other architectures, the source code must be recompiled for those architectures.

In terms of execution, native machine code requires no further translation and can be executed as soon as the code is compiled successfully (including any and all shared libraries required by the executable). Java byte code requires that the Java virtual machine be memory-resident during execution as the byte code must be interpreted to produce native machine code while the byte code is executing within the virtual machine.

In terms of memory consumption, C++ programs require no additional memory over and above the program's requirements. Java programs require additional memory for the Java virtual machine runtime. Java programs also consume additional memory to assist in memory management, such as automatic garbage collection. C++ programs manage their own memory using resource handles and smart pointers; the use of a garbage collector is optional.

In terms of performance, C++ programs execute many times more quickly than equivalent Java programs due to Java's need to interpret the byte code.