Introduction to Compiling Java

See Bucs.java

• A program is made up of one or more classes
• A class contains one or more methods
• A method contains program statements
• A Java application always executes the main method

Programming Language

machine language

assembly language

high-level language

fourth-generation language

• A compiler is a software tool which translates source code into a specific target language
• Often, that target language is the machine language for a particular CPU type
• The Java approach is somewhat different
• The Java compiler translates Java source code into a special representation called bytecode
• Java bytecode is not the machine language for any traditional CPU
• Another software tool, called an interpreter, translates bytecode into machine language and executes it
• Therefore the Java compiler is not tied to any particular machine
• Java is considered to be architecture-neutral

Step in Java Process

• 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!");