Java in a Nutshell, 5th Edition [Electronic resources] نسخه متنی

Synopsis

Description

javac

is the Java compiler; it compiles Java source code (in

.java files) into Java byte codes (in

.class files). The Java compiler is itself
written in Java.

javac can be passed any number of Java source
files, whose names must all end with the

.java
extension.

javac produces a separate

.class class file for each class defined in the
source files. Each source file can contain any number of classes,
although only one can be a public top-level class.
The name of the source file (minus the

.java
extension) must match the name of the public class
it contains.

In Java 1.2
and later, if a filename specified on the command line begins with
the character @, that file is taken not as a Java
source file but as a list of compiler options and Java source files.
Thus, if you keep a list of Java source files for a particular
project in a file named

project.list , you can
compile all those files at once with the command:

% javac @project.list

To compile a source file,

javac must be able to
find definitions of all classes used in the source file. It looks for
definitions in both source-file and class-file form, automatically
compiling any source files that have no corresponding class files or
that have been modified since they were most recently compiled.

Common options

The most commonly used compilation options
include the following:

-classpath path

Specifies the path

javac uses to look up classes
referenced in the specified source code. This option overrides any
path specified by the CLASSPATH environment
variable. The path specified is an ordered
list of directories, ZIP files, and JAR archives, separated by colons
on Unix systems or semicolons on Windows systems. If the
-sourcepath option is not set, this option also
specifies the search path for source files.

-d directory

Specifies the directory in which (or beneath which) class files
should be stored. By default,

javac stores the

.class files it generates in the same directory
as the

.java files those classes were defined
in. If the -d option is specified, however, the
specified directory is treated as the root
of the class hierarchy, and

.class files are
placed in this directory or the appropriate subdirectory below it,
depending on the package name of the class. Thus, the following
command:

% javac -d /java/classes Checkers.java

places the file

Checkers.class in the directory

/java/classes if the

Checkers.java file has no
package statement. On the other hand, if the
source file specifies that it is in a package:

package com.davidflanagan.games;

the

.class file is stored in

/java/classes/com/davidflanagan/games . When the
-d option is specified,

javac
automatically creates any directories it needs to store its class
files in the appropriate place.

-encoding encoding-name

Specifies the name of the character encoding used by the source files
if it differs from the default platform encoding.

-g

Tells

javac to add line number, source file, and
local variable information to the output class files, for use by
debuggers. By default,

javac generates only the
line numbers.

-g:none

Tells

javac to include no debugging information
in the output class files. Java 1.2 and later.

-g :keyword-list

Tells

javac to output the types of debugging
information specified by the comma-separated
keyword-list. The valid keywords are:
source, which specifies source-file information;
lines, which specifies line number information;
and vars, which specifies local variable debugging
information. Java 1.2 and later.

-help

Prints a list of options. See also -X.

-J javaoption

Passes the argument javaoption directly
through to the Java interpreter. For example:
-J-Xmx32m. javaoption
should not contain spaces; if multiple arguments must be passed to
the interpreter, use multiple -J options. Java 1.1
and later.

-source release-number

Specifies the version of Java the code is written in. Legal values of

release-number are 5, 1.5, 1.4, and 1.3. The
options 5 and 1.5 are synonyms and are the default: the compiler
accepts all Java 5.0 language features. Use -source
1.4 to have the compiler ignore Java 5.0 language features
such as the enum keyword. Use -source
1.3 to have the compiler ignore the
assert keyword that was introduced in Java 1.4.
This option is available in Java 1.4 and later.

-sourcepath path

Specifies the list of
directories, ZIP files, and JAR archives that

javac searches when looking for source files.
The files found in this source path are compiled if no corresponding
class files are found or if the source files are newer than the class
files. By default, source files are searched for in the same places
class files are searched for. Java 1.2 and later.

-verbose

Tells the compiler to display messages about what it is doing. In
particular, it causes

javac to list all the
source files it compiles, including files that did not appear on the
command line.

-X

Tells the

javac compiler to display usage
information for its nonstandard options (all of which begin with
-X). Java 1.2 and later.

Warning options

The following options control the generation of warning messages by

javac
:

-deprecation

Tells

javac to issue a warning for every use of
a deprecated API. By default,

javac issues only
a single warning for each source file that uses deprecated APIs. Java
1.1 and later. In Java 5.0, this is a synonym for
-Xlint:deprecation.

-nowarn

Tells

javac not to print warning messages.
Errors are still reported as usual.

-Xlint

Enables all recommended warnings about program
"lint."
At the time of this writing, all the warnings detailed below are
recommended.

-Xlint :warnings

Enables or disables a comma-separated list of named warning types. At
the time of this writing, the available warning types are the
following. A named warning can be suppressed by preceding it with a
minus sign:

all

Enables all lint warnings.

deprecation

Warns about the use of deprecated APIs. See also
-deprecation.

fallthrough

Warns when a case in a switch
statement "falls through" to the
next case. See also -Xswitchcheck.

finally

Warns when a finally clause cannot complete
normally.

path

Warns if any path directories specified elsewhere on the command line
are nonexistent.

serial

Warns about Serializable classes that do not have
a serialVersionUID field.

unchecked

Provides detailed warnings about each unchecked use of a generic type.

-Xmaxerrors num

Don't print more than num
errors.

-Xmaxwarns num

Don't print more than num
warnings.

-Xstdout filename

Tells

javac to send warning and error messages
to the specified file instead of writing them to the console. Java
1.4 and later.

-Xswitchcheck

Warns about case clauses in
switch statements that "fall
through." In Java 5.0, use
-Xlint:fallthrough.

Cross-compilation options

The
following
options are useful when
using

javac to compile class files intended to
run under a different version of Java:

-bootclasspath path

Specifies the search path

javac uses to look up
system classes. This option does not specify the system classes used
to run the compiler itself, only the system classes read by the
compiler. Java 1.2 and later.

-endorseddirs path

Overrides the directories to search for endorsed standards JAR files.

-extdirs path

Specifies a list of directories to search for standard extension JAR
files. Java 1.2 and later.

-target version

Specifies the class file format version to use for the generated
class files.

version may be 1.1, 1.2, 1.3, 1.4,
1.5, or 5. The options 1.5 and 5 are synonyms and are the default in
Java 5.0, unless -source 1.4 is specified, in
which case -target 1.4 is the default. Use of this
flag sets the class file version number so that the resulting class
file cannot be run by VMs from previous releases.

-Xbootclasspath :path

An alternative to -bootclasspath

-Xbootclasspath/a :path

Appends the specified path to the
bootclasspath. Java 1.3 and later.

-Xbootclasspath/p :path

Prefixes the bootclasspath with the specified
path.

Environment

CLASSPATH

Specifies an ordered list
(colon-separated on Unix, semicolon-separated on Windows systems) of
directories, ZIP files, and JAR archives in which

javac should look for user class files and
source files. This variable is overridden by the
-classpath option.

See also

java ,

jdb