javac - Java programming language compiler

This page is an abbreviated version of  http://java.sun.com/j2se/1.4.2/docs/tooldocs/solaris/javac.html

SYNOPSIS

javac [ options ] [ sourcefiles ] [ @argfiles ]

Arguments may be in any order.

options

Command-line options.

sourcefiles

One or more source files to be compiled (such as MyClass.java).

@argfiles

One or more files that lists options and source files.

DESCRIPTION

• In the description that follows, assume that the javac command is executed when your working directory is projects.
• Arrange source files in a directory tree that reflects their package tree.

• By default, the compiler puts each class file in the same directory as its source file.

SEARCHING FOR TYPES

• The compiler needs type information for every class or interface used, extended, or implemented in the source file.
• This includes classes and interfaces not explicitly mentioned in the source file but which provide information through inheritance.

• When the compiler needs type information, it looks for a source file or class file which defines the type.
• The compiler search order is:
  
1. bootstrap classes
2. extension classes
3. user class path.
• The user class path is defined by using the -classpath command line option.
• If you use the -sourcepath option, the compiler searches the indicated path for source files.
• Otherwise, the compiler searches the user class path both for class files and source files.
• A successful type search may produce a class file, a source file, or both.
  
• Here is how javac handles each situation:
• Search produces a class file but no source file: javac uses the class file.
• Search produces a source file but no class file: javac compiles the source file and uses the resulting class file.
• Search produces both a source file and a class file:
  

• javac can silently compile source files not mentioned on the command line.
  
• Use the -verbose option to trace automatic compilation.

OPTIONS

Standard Options

-classpath classpath

• Set the user class path.
  
• Again, if the -sourcepath option is not specified, the user class path is searched for source files as well as class files.

-d directory

• Set the destination directory for class files.
  
• The destination directory must already exist; javac does not create the destination directory.
  
• If a class is part of a package, javac puts the class file in a subdirectory reflecting the package name, creating directories as needed.
  

-help

-source 1.4

-sourcepath sourcepath

• Specify the source code path to search for class or interface definitions.
  
• Source path entries are separated by colons (:) and can be directories, JAR archives, or ZIP archives.
  
• If packages are used, the local path name within the directory or archive must reflect the package name.

COMMAND LINE ARGUMENT FILES

• To shorten or simplify the javac command line, you can specify one or more files that themselves contain arguments to the javac command.
  
• This enables you to create javac commands of any length on any operating system.
  
• An argument file can include javac options and source filenames in any combination.
  
• The arguments within a file can be space-separated or newline-separated.
  
• Filenames within an argument file are relative to the current directory, not the location of the argument file.
  
• Wildcards (*) are not allowed in these lists (such as for specifying *.java).
  
• Use of the '@' character to recursively interpret files is not supported.
  
• When executing javac, pass in the path and name of each argument file with the '@' leading character.
  
• When javac encounters an argument beginning with the character `@', it expands the contents of that file into the argument list.

Example - Single Arg File

  C:> javac @argfile

Example - Two Arg Files

Create a file named "options" containing:

     -d classes
     -sourcepath \java\pubs\ws\1_4\src\share\classes

Create a file named "classes" containing:

     MyClass1.java
     MyClass2.java
     MyClass3.java

  C:> javac @options @classes

Example - Arg Files with Paths

  C:> javac @path1\options @path2\classes

EXAMPLES

Compiling a Simple Program

• One source file, Hello.java, defines a class called greetings.Hello.
  
• The greetings directory is the package directory both for the source file and the class file and is in the current directory.
  
• This allows us to use the default user class path.
  
• It also makes it unnecessary to specify a separate destination directory with -d.

% ls
greetings/
% ls greetings
Hello.java
% cat greetings/Hello.java
package greetings;

public class Hello {
    public static void main(String[] args) {
        for (int i=0; i < args.length; i++) {
            System.out.println("Hello " + args[i]);
        }
    }
}
% javac greetings/Hello.java
% ls greetings
Hello.class   Hello.java
% java greetings.Hello World Universe Everyone
Hello World
Hello Universe
Hello Everyone

Compiling Multiple Source Files

This example compiles all the source files in the package greetings.

% ls
greetings/
% ls greetings
Aloha.java         GutenTag.java      Hello.java         Hi.java
% javac greetings/*.java
% ls greetings
Aloha.class         GutenTag.class      Hello.class         Hi.class
Aloha.java          GutenTag.java       Hello.java          Hi.java

Specifying a User Class Path

Having changed one of the source files in the previous example, we recompile it:

% pwd
/examples
% javac greetings/Hi.java

• Since greetings.Hi refers to other classes in the greetings package, the compiler needs to find these other classes.
  
• The example above works, because our default user class path happens to be the directory containing the package directory.
  
• But suppose we want to recompile this file and not worry about which directory we're in?
  
• Then, we need to add /examples to the user class path.
  

% javac -classpath /examples /examples/greetings/Hi.java

If we change greetings.Hi again, to use a banner utility, that utility also needs to be accessible through the user class path.

% javac -classpath /examples:/lib/Banners.jar /examples/greetings/Hi.java

To execute a class in greetings, we need access to greetings and to the classes it uses.

% java -classpath /examples:/lib/Banners.jar greetings.Hi

Separating Source Files and Class Files

• It often makes sense to keep source files and class files in separate directories on large projects.
  
• We use -d to indicate the separate class file destination.
  
• Since the source files are not in the user class path, we use -sourcepath to direct the compiler to them.

% ls
classes/  lib/      src/
% ls src
farewells/
% ls src/farewells
Base.java      GoodBye.java
% ls lib
Banners.jar
% ls classes
% javac -sourcepath src -classpath classes:lib/Banners.jar src/farewells/GoodBye.java -d classes
% ls classes
farewells/
% ls classes/farewells
Base.class      GoodBye.class

• The compiler compiled src/farewells/Base.java, even though we didn't specify it on the command line.
  
• To trace automatic compiles, use the -verbose option.

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