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

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

@argfiles

1 or more files that lists options and source files.

DESCRIPTION

• 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.
• If the -sourcepath option is specified, the compiler searches the indicated path for source files.
• Otherwise, the compiler searches the user classpath both for class files and source files.
• A successful type search may produce a class file, a source file, or both.
  
• If the search produces:
• a class file but no source file: javac uses the class file.
•  a source file but no class file: javac compiles the source file and uses the resulting class file.
• 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

• Again, if the -sourcepath option is unspecified, the class path is searched for source files and 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

-sourcepath sourcepath

• Specify the source code path to search for class or interface definitions.
  
• Source path entries are separated by a colon (:) 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.

EXAMPLES

Compiling a Simple Program

• 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 is 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 1 of the source files in the previous example, we recompile it:

% 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; the default class path (the current directory) contains the package directory, greetings.
  
• Suppose we want to recompile this file and not worry about which directory we're in?
  
• Then, we need to use full paths in the class path.
  

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

If we change greetings.Hi to use a utility, that utility needs to be accessible via the class path.

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

Separating Source Files and Class Files

• It often makes sense to separate source files from class files.
  
• 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.
• In the example below, GoodBye.java is in a package named farewells;

% 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 \
        -d classes \
         src/farewells/GoodBye.java
% ls classes
farewells/
% ls classes/farewells
Base.class      GoodBye.class

• The compiler compiled Base.java, even though we didn't specify it on the command line.

Exercises

• In the exercises below:
• Main.java uses MyQ.java
• Neither has a package statement
• Based on the directory structure below, give a javac command:

1. Executed while in the cs50 directory that:
• compiles Main.java,
• puts the .class file in the same directory as Main.java
2. Executed while in the cs50 directory that compiles: 
• compiles MainTest.java
• puts the .class file in the same directory as MainTest.java
• needs classes in junit.jar
3. Executed while in the cs50 directory that compiles: 
• compiles: MainTest.java
• puts the .class file in the same directory as MainTest.java
• needs classes in junit.jar and jogl.jar
4. Executed while in the cs50 directory that compiles: 
• compiles: Main.java and MainTest.java
• puts the .class files in the same directory as their respective .java files
• needs classes in junit.jar and jogl.jar
5. Executed while in the cs50 directory that compiles: 
• compiles: Main.java and MainTest.java
• needs classes in junit.jar and jogl.jar
• puts the .class files in the class directory (what 2 .class files are put in the class tree that are not shown?)
6. Executed while in the cs50 directory that compiles, using the -sourcepath option: 
• compiles: MainTest.java and MainTest.java
• needs classes in junit.jar and jogl.jar
• puts the .class files in the class directory
7. Executed while in the cs50 directory that compiles, using the -sourcepath option: 
• compiles: MyQ.java, Main.java, and MainTest.java
• needs classes in junit.jar and jogl.jar
• puts the .class files in the class directory
8. Executed while in the cs50 directory that compiles, using the -sourcepath option: 
• compiles: MyQ.java, Main.java, and MainTest.java, only if needed.
• needs classes in junit.jar and jogl.jar
• puts the .class files in the class directory

1. Executed while in the smith directory that compiles, using the -sourcepath option: 
• compiles: MyQ.java, Main.java, and MainTest.java, only if needed.
• needs classes in junit.jar and jogl.jar
• puts the .class files in the class directory