javac

NAME

SYNOPSIS

PARAMETERS

sourcefiles

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

@files

One or more files that list source files.

DESCRIPTION

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

*

For a small number of source files, simply list the file names on the command line.

*

For a large number of source files, list the the file names in a file, separated by blanks or line breaks. Then use the list file name on the javac command line, preceded by an @ character.

Source code file names must have .java suffixes, class file names must have .class suffixes, and both source and class files must have root names that identify the class. For example, a class called MyClass would be written in a source file called MyClass.java and compiled into a bytecode class file called MyClass.class.

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. 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:

*

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 determines whether the class file is out of date. If the class file is out of date, javac recompiles the source file and uses the updated class file. Otherwise, javac just uses the class file.

By default, javac considers a class file out of date only if it is older than the source file.

Note that 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

Sets the user class path, overriding the user class path in the CLASSPATH environment variable. If neither CLASSPATH or -classpath is specified, the user class path consists of the current directory. See Setting the Class Path for more details.

If the -sourcepath option is not specified, the user class path is searched for source files as well as class files.

-d directory

Sets the destination directory for class files. The destination directory must already exist; javac will 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. For example, if you specify -d /home/myclasses and the class is called com.mypackage.MyClass, then the class file is called /home/myclasses/com/mypackage/MyClass.class.

If -d is not specified, javac puts the class file in the same directory as the source file.

Note that the directory specified by -d is not automatically added to your user class path.

-deprecation

Shows a description of each use or override of a deprecated member or class. Without -deprecation, javac shows the names of source files that use or override deprecated members or classes.

-encoding encoding

Sets the source file encoding name, such as EUCJIS/SJIS. If -encoding is not specified, the platform default converter is used.

-g

Generates all debugging information, including local variables. By default, only line number and source file information is generated.

-g:none

Does not generate any debugging information.

-g:keyword-list

Generates only some kinds of debugging information, specified by a comma separated list of keywords. Valid keywords are:

source

Source file debugging information

lines

Line number debugging information

vars

Local variable debugging information

-help

Prints a synopsis of standard options.

-nowarn

Disables warning messages.

-source release

Enables support for compiling source code containing assertions.

When release is set to 1.4, the compiler accepts code containing assertions. Assertions were introduced in J2SE 1.4.

When release is set to 1.3, the compiler does not support assertions. The compiler defaults to the 1.3-behavior if the -source flag is not used.

-sourcepath sourcepath

Specifies the source code path to search for class or interface definitions. As with the user class path, 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.

Note that classes found through the classpath are subject to automatic recompilation if their sources are found.

-verbose

Verbose output. This includes information about each class loaded and each source file compiled.

Cross-Compilation Options

-bootclasspath bootclasspath

Cross-compiles against the specified set of boot classes. As with the user class path, boot class path entries are separated by colons (:) and can be directories, JAR archives, or ZIP archives.

-extdirs directories

Cross-compiles against the specified extension directories. Directories are a colon-separated list of directories. Each JAR archive in the specified directories is searched for class files.

-target version

Generates class files that will work on VMs with the specified version. The default is to generate class files to be compatible with 1.2 VMs, with one exception. When the -source 1.4 option is used, the default target is 1.4. The versions supported are:

1.1

Ensures that generated class files will be compatible with 1.1 and 1.2 VMs.

1.2

Generates class files that will run on 1.2 VMs, but will not run on 1.1 VMs. This is the default.

1.3

Generates class files that run on VMs in the Java 2 SDK, v1.3 and later, but will not run on 1.1 or 1.2 VMs.

1.4

Generates class files that are compatible only with 1.4 VMs.

Non-Standard Options

-Joption

Passes option to the java launcher called by javac. For example, -J-Xms48m sets the startup memory to 48 megabytes. Although it does not begin with -X, it is not a `standard option' of javac. It is a common convention for -J to pass options to the underlying VM executing applications written in Java.

Note that CLASSPATH, -classpath, -bootclasspath, and -extdirs do not specify the classes used to run javac. Fiddling with the implementation of the compiler in this way is usually pointless and always risky. If you do need to do this, use the -J option to pass through options to the underlying java launcher.

-X

Displays information about non-standard options and exit.

-Xstdout filename

Send compiler messages to the named file. By default, compiler messages go to System.err.

-Xswitchcheck

Checks switch blocks for fall-through cases and provides a warning message for any that are found. Fall-through cases are cases in a switch block, other than the last case in the block, whose code does not include a break statement, allowing code execution to "fall through" from that case to the next case. For example, the code following the case 1 label in this switch block does not contain a break statement:

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

If the -Xswtichcheck flag were used when compiling this code, the compiler would emit a warning about "possible fall-through into case," along with the line number of the case in question.

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

Create a file named

classes containing:

MyClass1.java
MyClass2.java
MyClass3.java

You would then run javac with:

C:> javac @options @classes

Example - Arg Files with Paths

   example% ls
      greetings/
   example% ls greetings
      Hello.java
   example% 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]);
              }
           }
      }
   example% javac greetings/Hello.java
   example% ls greetings
      Hello.class   Hello.java
   example% java greetings.Hello World Universe Everyone
      Hello World
      Hello Universe
      Hello Everyone

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

   example% pwd
      /examples
   example% javac greetings/Hi.java

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

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

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

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

   example% javac -target 1.1 -bootclasspath jdk1.1.7/lib/classes.zip \
        -extdirs "" OldCode.java