Question

After reading some material on this subject I’m still not sure what the difference between a compiled language and an interpreted language is. I was told this is one of the differences between Java and JavaScript. Would someone please help me in understanding it?

Answer 1

What’s the difference between compiled and interpreted language?

The difference is not in the language; it is in the implementation.

Having got that out of my system, here’s an answer:

• In a compiled implementation, the original program is translated into native machine instructions, which are executed directly by the hardware.

• In an interpreted implementation, the original program is translated into something else. Another program, called “the interpreter”, then examines “something else” and performs whatever actions are called for. Depending on the language and its implementation, there are a variety of forms of “something else”. From more popular to less popular, “something else” might be

  • Binary instructions for a virtual machine, often called bytecode, as is done in Lua, Python, Ruby, Smalltalk, and many other systems (the approach was popularized in the 1970s by the UCSD P-system and UCSD Pascal)

  • A tree-like representation of the original program, such as an abstract-syntax tree, as is done for many prototype or educational interpreters

  • A tokenized representation of the source program, similar to Tcl

  • The characters of the source program, as was done in MINT and TRAC

One thing that complicates the issue is that it is possible to translate (compile) bytecode into native machine instructions. Thus, a successful intepreted implementation might eventually acquire a compiler. If the compiler runs dynamically, behind the scenes, it is often called a just-in-time compiler or JIT compiler. JITs have been developed for Java, JavaScript, Lua, and I daresay many other languages. At that point you can have a hybrid implementation in which some code is interpreted and some code is compiled.