javac - Unix, Linux Command

NAME

SYNOPSIS

PARAMETERS

DESCRIPTION

There are two ways to pass source code file names to javac:

Inner class definitions produce additional class files. These class files have names combining the inner and outer class names, such as MyClass$MyInnerClass.class.

You should arrange source files in a directory tree that reflects their package tree. For example, if you keep all your source files in /workspace, the source code for com.mysoft.mypack.MyClass should be in /workspace/com/mysoft/mypack/MyClass.java.

By default, the compiler puts each class file in the same directory as its source file. You can specify a separate destination directory with -d (see OPTIONS, below).

Searching for Types

For example, when you subclass java.applet.Applet, you are also using Applet’s ancestor classes: java.awt.Panel, java.awt.Container, java.awt.Component, and java.awt.Object.

When the compiler needs type information, it looks for a source file or class file which defines the type. The compiler searches first in the bootstrap and extension classes, then in the user class path (which by default is the current directory). The user class path is defined by setting the CLASSPATH environment variable or by using the -classpath command line option. (For details, see Setting the Class Path.)

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. You can specify different bootstrap or extension classes with the -bootclasspath and -extdirs options; see Cross-Compilation Options below.

A successful type search may produce a class file, a source file, or both. Here is how javac handles each situation:

OPTIONS

Standard Options

Cross-Compilation Options

Non-Standard Options

switch (x) {
case 1:
           System.out.println("1");
                //  No  break;  statement here.
case 2:
           System.out.println("2");
}

THE -J OPTION

COMMAND LINE ARGUMENT FILES

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

This argument file could contain the contents of both files shown in the next example.

Example - Two Arg Files

Create a file named options containing:

-d classes
-g
-sourcepath \java\pubs\ws\1.3\src\share\classes

MyClass1.java
MyClass2.java
MyClass3.java

% javac @options @classes

Example - Arg Files with Paths

% javac @path1/options @path2/classes

EXAMPLES

Compiling a Simple Program

   % 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

   % 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

   % 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. We can do this by setting CLASSPATH, but here we’ll use the -classpath option.

   % 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 both to greetings and to the classes it uses.

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

Separating Source Files and Class Files

   % 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

Note: 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.

Cross-Compilation Example

   % javac -target 1.4 -bootclasspath jdk1.4.2/lib/classes.zip \
        -extdirs "" OldCode.java

The -target 1.4 option ensures that the generated class files will be compatible with 1.4 VMs. BY default, javac compiles for 1.5.

The Java 2 SDk’s javac would also by default compile against its own bootstrap classes, so we need to tell javac to compile against JDK 1.4 bootstrap classes instead. We do this with -bootclasspath and -extdirs. Failing to do this might allow compilation against a Java 2 Platform API that would not be present on a 1.4 VM and would fail at runtime.

SEE ALSO

• jar (1)

• java (1)

• javadoc (1)

• javah (1)

• javap (1)

• jdb (1)