Computer Science 1 Top Lectures Assignments Noticeboard Java Mechanics

Mechanics

Edit/Translate/Execute Process in General

• Edit - Program source is stored in a file. Written, modified, updated using an editor.
• Translate - Program source is converted from its textual form into a form that can be executed by a machine (i.e., machine code or machine language)
  • Compile - translate from high-level programming language to machine code all in one shot
  • Interpret - translate from high-level programming language to machine code a statement at a time, throwing away machine code for the statement after it has been executed
• Execute - Machine code is executed on the machine

Edit/Translate/Execute Process in Java



• Edit -
  • Each file contains a single class
  • Use comment header!
  • File name is X.java, where the name X is the name of the class.
• Translate - uses both compile and interpreter
  • javac X.java - Compile X.java into X.class
  • X.class is not machine code - it is called java byte code
  • X.class is executed by a Java interpreter
  • Many languages are compiled (since it is efficient)! Why this approach?
    • Portability, sharing
    • Embed byte code in WWW browsers
• Execute -
  • java X

Time

• Different times in programming
  • program writing time - when program is being edited
  • compile time - when program is being translated
  • execute time - when program is being executed
• Different times in Java programming
  • program writing time - comments written when writing code, ignored by compiler, never executed
  • detect errors at compile time - spelling errors, typos
    • system.out.println ("foo");
    • Systemoutprintln ("foo");
    • system.out.println ("foo);
  • execute time - statements in wrong order, mistakes in strings
    • System.out.println ("Print this second"); System.outprintln ("Print this first");
    • System.out.println ("Komputer Science is fun!");

Terminology