javac(1) Basic Tools javac(1)NAMEjavac - Reads Java class and interface definitions and compiles them
into bytecode and class files.
SYNOPSISjavac [ options ] [ sourcefiles ] [ classes] [ @argfiles ]
Arguments can be in any order:
options
Command-line options. See Options.
sourcefiles
One or more source files to be compiled (such as MyClass.java).
classes
One or more classes to be processed for annotations (such as
MyPackage.MyClass).
@argfiles
One or more files that list options and source files. The -J
options are not allowed in these files. See Command-Line
Argument Files.
DESCRIPTION
The javac command reads class and interface definitions, written in the
Java programming language, and compiles them into bytecode class files.
The javac command can also process annotations in Java source files and
classes.
There are two ways to pass source code file names to javac.
· For a small number of source files, list the file names on the
command line.
· For a large number of source files, list the file names in a file
that is separated by blanks or line breaks. Use the list file name
preceded by an at sign (@) with the javac command.
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 that combine the inner and outer class names, such as
MyClass$MyInnerClass.class.
Arrange source files in a directory tree that reflects their package
tree. For example, if all of your source files are in /workspace, then
put the source code for com.mysoft.mypack.MyClass 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
the -d option.
OPTIONS
The compiler has a set of standard options that are supported on the
current development environment. An additional set of nonstandard
options are specific to the current virtual machine and compiler
implementations and are subject to change in the future. Nonstandard
options begin with the -X option.
· See also Cross-Compilation Options
· See also Nonstandard Options
STANDARD OPTIONS
-Akey[=value]
Specifies options to pass to annotation processors. These
options are not interpreted by javac directly, but are made
available for use by individual processors. The key value should
be one or more identifiers separated by a dot (.).
-cp path or -classpath path
Specifies where to find user class files, and (optionally)
annotation processors and source files. This class path
overrides the user class path in the CLASSPATH environment
variable. If neither CLASSPATH, -cp nor -classpath is specified,
then the user class path is the current directory. See Setting
the Class Path.
If the -sourcepath option is not specified, then the user class
path is also searched for source files.
If the -processorpath option is not specified, then the class
path is also searched for annotation processors.
-Djava.ext.dirs=directories
Overrides the location of installed extensions.
-Djava.endorsed.dirs=directories
Overrides the location of the endorsed standards path.
-d directory
Sets the destination directory for class files. The directory
must already exist because javac does not create it. If a class
is part of a package, then javac puts the class file in a
subdirectory that reflects the package name and creates
directories as needed.
If you specify -d/home/myclasses and the class is called
com.mypackage.MyClass, then the class file is
/home/myclasses/com/mypackage/MyClass.class.
If the -d option is not specified, then javac puts each class
file in the same directory as the source file from which it was
generated.
Note: The directory specified by the -d option 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 the -deprecation option, javac shows a
summary of the source files that use or override deprecated
members or classes. The -deprecation option is shorthand for
-Xlint:deprecation.
-encoding encoding
Sets the source file encoding name, such as EUC-JP and UTF-8. If
the -encoding option is not specified, then the platform default
converter is used.
-endorseddirs directories
Overrides the location of the endorsed standards path.
-extdirs directories
Overrides the location of the ext directory. The directories
variable is a colon-separated list of directories. Each JAR file
in the specified directories is searched for class files. All
JAR files found become part of the class path.
If you are cross-compiling (compiling classes against bootstrap
and extension classes of a different Java platform
implementation), then this option specifies the directories that
contain the extension classes. See Cross-Compilation Options for
more information.
-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.
-implicit:[class, none]
Controls the generation of class files for implicitly loaded
source files. To automatically generate class files, use
-implicit:class. To suppress class file generation, use
-implicit:none. If this option is not specified, then the
default is to automatically generate class files. In this case,
the compiler issues a warning if any such class files are
generated when also doing annotation processing. The warning is
not issued when the -implicit option is set explicitly. See
Searching for Types.
-Joption
Passes option to the Java Virtual Machine (JVM), where option is
one of the options described on the reference page for the Java
launcher. For example, -J-Xms48m sets the startup memory to 48
MB. See java(1).
Note: The CLASSPATH, -classpath, -bootclasspath, and -extdirs
options do not specify the classes used to run javac. Trying to
customize the compiler implementation with these options and
variables is risky and often does not accomplish what you want.
If you must customize the complier implementation, then use the
-J option to pass options through to the underlying Java
launcher.
-nowarn
Disables warning messages. This option operates the same as the
-Xlint:none option.
-parameters
Stores formal parameter names of constructors and methods in the
generated class file so that the method
java.lang.reflect.Executable.getParameters from the Reflection
API can retrieve them.
-proc: [none, only]
Controls whether annotation processing and compilation are done.
-proc:none means that compilation takes place without annotation
processing. -proc:only means that only annotation processing is
done, without any subsequent compilation.
-processor class1 [,class2,class3...]
Names of the annotation processors to run. This bypasses the
default discovery process.
-processorpath path
Specifies where to find annotation processors. If this option is
not used, then the class path is searched for processors.
-s dir
Specifies the directory where to place the generated source
files. The directory must already exist because javac does not
create it. If a class is part of a package, then the compiler
puts the source file in a subdirectory that reflects the package
name and creates directories as needed.
If you specify -s /home/mysrc and the class is called
com.mypackage.MyClass, then the source file is put in
/home/mysrc/com/mypackage/MyClass.java.
-source release
Specifies the version of source code accepted. The following
values for release are allowed:
1.3 The compiler does not support assertions, generics, or
other language features introduced after Java SE 1.3.
1.4 The compiler accepts code containing assertions, which
were introduced in Java SE 1.4.
1.5 The compiler accepts code containing generics and other
language features introduced in Java SE 5.
5 Synonym for 1.5.
1.6 No language changes were introduced in Java SE 6.
However, encoding errors in source files are now reported
as errors instead of warnings as in earlier releases of
Java Platform, Standard Edition.
6 Synonym for 1.6.
1.7 The compiler accepts code with features introduced in
Java SE 7.
7 Synonym for 1.7.
1.8 This is the default value. The compiler accepts code with
features introduced in Java SE 8.
8 Synonym for 1.8.
-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 (:) on Oracle Solaris and semicolons on
Windows and can be directories, JAR archives, or ZIP archives.
If packages are used, then the local path name within the
directory or archive must reflect the package name.
Note: Classes found through the class path might be recompiled
when their source files are also found. See Searching for Types.
-verbose
Uses verbose output, which includes information about each class
loaded and each source file compiled.
-version
Prints release information.
-werror
Terminates compilation when warnings occur.
-X
Displays information about nonstandard options and exits.
CROSS-COMPILATION OPTIONS
By default, classes are compiled against the bootstrap and extension
classes of the platform that javac shipped with. But javac also
supports cross-compiling, where classes are compiled against a
bootstrap and extension classes of a different Java platform
implementation. It is important to use the -bootclasspath and -extdirs
options when cross-compiling.
-target version
Generates class files that target a specified release of the
virtual machine. Class files will run on the specified target
and on later releases, but not on earlier releases of the JVM.
Valid targets are 1.1, 1.2, 1.3, 1.4, 1.5 (also 5), 1.6 (also
6), 1.7 (also 7), and 1.8 (also 8).
The default for the -target option depends on the value of the
-source option:
· If the -source option is not specified, then the value of the
-target option is 1.8
· If the -source option is 1.2, then the value of the -target
option is 1.4
· If the -source option is 1.3, then the value of the -target
option is 1.4
· If the -source option is 1.5, then the value of the -target
option is 1.8
· If the -source option is 1.6, then the value of the -target is
option 1.8
· If the -source option is 1.7, then the value of the -target is
option 1.8
· For all other values of the -source option, the value of the
-target option is the value of the -source option.
-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.
COMPACT PROFILE OPTION
Beginning with JDK 8, the javac compiler supports compact profiles.
With compact profiles, applications that do not require the entire Java
platform can be deployed and run with a smaller footprint. The compact
profiles feature could be used to shorten the download time for
applications from app stores. This feature makes for more compact
deployment of Java applications that bundle the JRE. This feature is
also useful in small devices.
The supported profile values are compact1, compact2, and compact3.
These are additive layers. Each higher-numbered compact profile
contains all of the APIs in profiles with smaller number names.
-profile
When using compact profiles, this option specifies the profile
name when compiling. For example:
javac-profile compact1 Hello.java
javac does not compile source code that uses any Java SE APIs
that is not in the specified profile. Here is an example of the
error message that results from attempting to compile such
source code:
cd jdk1.8.0/bin
./javac -profile compact1 Paint.java
Paint.java:5: error: Applet is not available in profile 'compact1'
import java.applet.Applet;
In this example, you can correct the error by modifying the
source to not use the Applet class. You could also correct the
error by compiling without the -profile option. Then the
compilation would be run against the full set of Java SE APIs.
(None of the compact profiles include the Applet class.)
An alternative way to compile with compact profiles is to use
the -bootclasspath option to specify a path to an rt.jar file
that specifies a profile's image. Using the -profile option
instead does not require a profile image to be present on the
system at compile time. This is useful when cross-compiling.
NONSTANDARD OPTIONS
-Xbootclasspath/p:path
Adds a suffix to the bootstrap class path.
-Xbootclasspath/a:path
Adds a prefix to the bootstrap class path.
-Xbootclasspath/:path
Overrides the location of the bootstrap class files.
-Xdoclint:[-]group [/access]
Enables or disables specific groups of checks, where group is
one of the following values: accessibility, syntax, reference,
html or missing. For more information about these groups of
checks see the -Xdoclint option of the javadoc command. The
-Xdoclint option is disabled by default in the javac command.
The variable access specifies the minimum visibility level of
classes and members that the -Xdoclint option checks. It can
have one of the following values (in order of most to least
visible) : public, protected, package and private. For example,
the following option checks classes and members (with all groups
of checks) that have the access level protected and higher
(which includes protected, package and public):
-Xdoclint:all/protected
The following option enables all groups of checks for all access
levels, except it will not check for HTML errors for classes and
members that have access level package and higher (which
includes package and public):
-Xdoclint:all,-html/package
-Xdoclint:none
Disables all groups of checks.
-Xdoclint:all[/access]
Enables all groups of checks.
-Xlint
Enables all recommended warnings. In this release, enabling all
available warnings is recommended.
-Xlint:all
Enables all recommended warnings. In this release, enabling all
available warnings is recommended.
-Xlint:none
Disables all warnings.
-Xlint:name
Disables warning name. See Enable or Disable Warnings with the
-Xlint Option for a list of warnings you can disable with this
option.
-Xlint:-name
Disables warning name. See Enable or Disable Warnings with the
-Xlint Option with the -Xlint option to get a list of warnings
that you can disable with this option.
-Xmaxerrs number
Sets the maximum number of errors to print.
-Xmaxwarns number
Sets the maximum number of warnings to print.
-Xstdout filename
Sends compiler messages to the named file. By default, compiler
messages go to System.err.
-Xprefer:[newer,source]
Specifies which file to read when both a source file and class
file are found for a type. (See Searching for Types). If the
-Xprefer:newer option is used, then it reads the newer of the
source or class file for a type (default). If the
-Xprefer:source option is used, then it reads the source file.
Use -Xprefer:source when you want to be sure that any annotation
processors can access annotations declared with a retention
policy of SOURCE.
-Xpkginfo:[always,legacy,nonempty]
Control whether javac generates package-info.class files from
package-info.java files. Possible mode arguments for this option
include the following.
always Always generate a package-info.class file for every
package-info.java file. This option may be useful if you
use a build system such as Ant, which checks that each
.java file has a corresponding .class file.
legacy Generate a package-info.class file only if package-
info.java contains annotations. Don't generate a package-
info.class file if package-info.java only contains
comments.
Note: A package-info.class file might be generated but be
empty if all the annotations in the package-info.java
file have RetentionPolicy.SOURCE.
nonempty
Generate a package-info.class file only if package-
info.java contains annotations with RetentionPolicy.CLASS
or RetentionPolicy.RUNTIME.
-Xprint
Prints a textual representation of specified types for debugging
purposes. Perform neither annotation processing nor compilation.
The format of the output could change.
-XprintProcessorInfo
Prints information about which annotations a processor is asked
to process.
-XprintRounds
Prints information about initial and subsequent annotation
processing rounds.
ENABLE OR DISABLE WARNINGS WITH THE -XLINT OPTION
Enable warning name with the -Xlint:name option, where name is one of
the following warning names. Note that you can disable a warning with
the -Xlint:-name: option.
cast Warns about unnecessary and redundant casts, for example:
String s = (String) "Hello!"
classfile
Warns about issues related to class file contents.
deprecation
Warns about the use of deprecated items, for example:
java.util.Date myDate = new java.util.Date();
int currentDay = myDate.getDay();
The method java.util.Date.getDay has been deprecated since JDK
1.1
dep-ann
Warns about items that are documented with an @deprecated
Javadoc comment, but do not have a @Deprecated annotation, for
example:
/**
* @deprecated As of Java SE 7, replaced by {@link #newMethod()}
*/
public static void deprecatedMethood() { }
public static void newMethod() { }
divzero
Warns about division by the constant integer 0, for example:
int divideByZero = 42 / 0;
empty Warns about empty statements after ifstatements, for example:
class E {
void m() {
if (true) ;
}
}
fallthrough
Checks the 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 end with a break statement:
switch (x) {
case 1:
System.out.println("1");
// No break statement here.
case 2:
System.out.println("2");
}
If the -Xlint:fallthrough option was used when compiling this
code, then the compiler emits a warning about possible fall-
through into case, with the line number of the case in question.
finally
Warns about finally clauses that cannot complete normally, for
example:
public static int m() {
try {
throw new NullPointerException();
} catch (NullPointerException(); {
System.err.println("Caught NullPointerException.");
return 1;
} finally {
return 0;
}
}
The compiler generates a warning for the finally block in this
example. When the int method is called, it returns a value of 0.
A finally block executes when the try block exits. In this
example, when control is transferred to the catch block, the int
method exits. However, the finally block must execute, so it is
executed, even though control was transferred outside the
method.
options
Warns about issues that related to the use of command-line
options. See Cross-Compilation Options.
overrides
Warns about issues regarding method overrides. For example,
consider the following two classes:
public class ClassWithVarargsMethod {
void varargsMethod(String... s) { }
}
public class ClassWithOverridingMethod extends ClassWithVarargsMethod {
@Override
void varargsMethod(String[] s) { }
}
The compiler generates a warning similar to the following:.
warning: [override] varargsMethod(String[]) in ClassWithOverridingMethod
overrides varargsMethod(String...) in ClassWithVarargsMethod; overriding
method is missing '...'
When the compiler encounters a varargs method, it translates the
varargs formal parameter into an array. In the method
ClassWithVarargsMethod.varargsMethod, the compiler translates
the varargs formal parameter String... s to the formal parameter
String[] s, an array, which matches the formal parameter of the
method ClassWithOverridingMethod.varargsMethod. Consequently,
this example compiles.
path Warns about invalid path elements and nonexistent path
directories on the command line (with regard to the class path,
the source path, and other paths). Such warnings cannot be
suppressed with the @SuppressWarnings annotation, for example:
javac -Xlint:path -classpath /nonexistentpath Example.java
processing
Warn about issues regarding annotation processing. The compiler
generates this warning when you have a class that has an
annotation, and you use an annotation processor that cannot
handle that type of exception. For example, the following is a
simple annotation processor:
Source file AnnocProc.java:
import java.util.*;
import javax.annotation.processing.*;
import javax.lang.model.*;
import.javaz.lang.model.element.*;
@SupportedAnnotationTypes("NotAnno")
public class AnnoProc extends AbstractProcessor {
public boolean process(Set<? extends TypeElement> elems, RoundEnvironment renv){
return true;
}
public SourceVersion getSupportedSourceVersion() {
return SourceVersion.latest();
}
}
Source file AnnosWithoutProcessors.java:
@interface Anno { }
@Anno
class AnnosWithoutProcessors { }
The following commands compile the annotation processor
AnnoProc, then run this annotation processor against the source
file AnnosWithoutProcessors.java:
javac AnnoProc.java
javac-cp . -Xlint:processing -processor AnnoProc -proc:only AnnosWithoutProcessors.java
When the compiler runs the annotation processor against the
source file AnnosWithoutProcessors.java, it generates the
following warning:
warning: [processing] No processor claimed any of these annotations: Anno
To resolve this issue, you can rename the annotation defined and
used in the class AnnosWithoutProcessors from Anno to NotAnno.
rawtypes
Warns about unchecked operations on raw types. The following
statement generates a rawtypes warning:
void countElements(List l) { ... }
The following example does not generate a rawtypes warning
void countElements(List<?> l) { ... }
List is a raw type. However, List<?> is an unbounded wildcard
parameterized type. Because List is a parameterized interface,
always specify its type argument. In this example, the List
formal argument is specified with an unbounded wildcard (?) as
its formal type parameter, which means that the countElements
method can accept any instantiation of the List interface.
Serial Warns about missing serialVersionUID definitions on serializable
classes, for example:
public class PersistentTime implements Serializable
{
private Date time;
public PersistentTime() {
time = Calendar.getInstance().getTime();
}
public Date getTime() {
return time;
}
}
The compiler generates the following warning:
warning: [serial] serializable class PersistentTime has no definition of
serialVersionUID
If a serializable class does not explicitly declare a field
named serialVersionUID, then the serialization runtime
environment calculates a default serialVersionUID value for that
class based on various aspects of the class, as described in the
Java Object Serialization Specification. However, it is strongly
recommended that all serializable classes explicitly declare
serialVersionUID values because the default process of computing
serialVersionUID vales is highly sensitive to class details that
can vary depending on compiler implementations, and as a result,
might cause an unexpected InvalidClassExceptions during
deserialization. To guarantee a consistent serialVersionUID
value across different Java compiler implementations, a
serializable class must declare an explicit serialVersionUID
value.
static Warns about issues relating to the use of statics, for example:
class XLintStatic {
static void m1() { }
void m2() { this.m1(); }
}
The compiler generates the following warning:
warning: [static] static method should be qualified by type name,
XLintStatic, instead of by an expression
To resolve this issue, you can call the static method m1 as
follows:
XLintStatic.m1();
Alternately, you can remove the static keyword from the
declaration of the method m1.
try Warns about issues relating to use of try blocks, including try-
with-resources statements. For example, a warning is generated
for the following statement because the resource ac declared in
the try block is not used:
try ( AutoCloseable ac = getResource() ) { // do nothing}
unchecked
Gives more detail for unchecked conversion warnings that are
mandated by the Java Language Specification, for example:
List l = new ArrayList<Number>();
List<String> ls = l; // unchecked warning
During type erasure, the types ArrayList<Number> and
List<String> become ArrayList and List, respectively.
The ls command has the parameterized type List<String>. When the
List referenced by l is assigned to ls, the compiler generates
an unchecked warning. At compile time, the compiler and JVM
cannot determine whether l refers to a List<String> type. In
this case, l does not refer to a List<String> type. As a result,
heap pollution occurs.
A heap pollution situation occurs when the List object l, whose
static type is List<Number>, is assigned to another List object,
ls, that has a different static type, List<String>. However, the
compiler still allows this assignment. It must allow this
assignment to preserve backward compatibility with releases of
Java SE that do not support generics. Because of type erasure,
List<Number> and List<String> both become List. Consequently,
the compiler allows the assignment of the object l, which has a
raw type of List, to the object ls.
varargs
Warns about unsafe usages of variable arguments (varargs)
methods, in particular, those that contain non-reifiable
arguments, for example:
public class ArrayBuilder {
public static <T> void addToList (List<T> listArg, T... elements) {
for (T x : elements) {
listArg.add(x);
}
}
}
Note: A non-reifiable type is a type whose type information is
not fully available at runtime.
The compiler generates the following warning for the definition
of the method ArrayBuilder.addToList
warning: [varargs] Possible heap pollution from parameterized vararg type T
When the compiler encounters a varargs method, it translates the
varargs formal parameter into an array. However, the Java
programming language does not permit the creation of arrays of
parameterized types. In the method ArrayBuilder.addToList, the
compiler translates the varargs formal parameter T... elements
to the formal parameter T[] elements, an array. However, because
of type erasure, the compiler converts the varargs formal
parameter to Object[] elements. Consequently, there is a
possibility of heap pollution.
COMMAND-LINE ARGUMENT FILES
To shorten or simplify the javac command, you can specify one or more
files that contain arguments to the javac command (except -J options).
This enables you to create javac commands of any length on any
operating system.
An argument file can include javac options and source file names in any
combination. The arguments within a file can be separated by spaces or
new line characters. If a file name contains embedded spaces, then put
the whole file name in double quotation marks.
File Names within an argument file are relative to the current
directory, not the location of the argument file. Wild cards (*) are
not allowed in these lists (such as for specifying *.java). Use of the
at sign (@) to recursively interpret files is not supported. The -J
options are not supported because they are passed to the launcher,
which does not support argument files.
When executing the javac command, pass in the path and name of each
argument file with the at sign (@) leading character. When the javac
command encounters an argument beginning with the at sign (@), it
expands the contents of that file into the argument list.
Example 1 Single Argument File
You could use a single argument file named argfile to hold all javac
arguments:
javac @argfile
This argument file could contain the contents of both files shown in
Example 2
Example 2 Two Argument Files
You can create two argument files: one for the javac options and the
other for the source file names. Note that the following lists have no
line-continuation characters.
Create a file named options that contains the following:
-d classes
-g
-sourcepath /java/pubs/ws/1.3/src/share/classes
Create a file named classes that contains the following:
MyClass1.java
MyClass2.java
MyClass3.java
Then, run the javac command as follows:
javac @options @classes
Example 3 Argument Files with Paths
The argument files can have paths, but any file names inside the files
are relative to the current working directory (not path1 or path2):
javac @path1/options @path2/classes
ANNOTATION PROCESSING
The javac command provides direct support for annotation processing,
superseding the need for the separate annotation processing command,
apt.
The API for annotation processors is defined in the
javax.annotation.processing and javax.lang.model packages and
subpackages.
HOW ANNOTATION PROCESSING WORKS
Unless annotation processing is disabled with the -proc:none option,
the compiler searches for any annotation processors that are available.
The search path can be specified with the -processorpath option. If no
path is specified, then the user class path is used. Processors are
located by means of service provider-configuration files named META-
INF/services/javax.annotation.processing.Processor on the search path.
Such files should contain the names of any annotation processors to be
used, listed one per line. Alternatively, processors can be specified
explicitly, using the -processor option.
After scanning the source files and classes on the command line to
determine what annotations are present, the compiler queries the
processors to determine what annotations they process. When a match is
found, the processor is called. A processor can claim the annotations
it processes, in which case no further attempt is made to find any
processors for those annotations. After all of the annotations are
claimed, the compiler does not search for additional processors.
If any processors generate new source files, then another round of
annotation processing occurs: Any newly generated source files are
scanned, and the annotations processed as before. Any processors called
on previous rounds are also called on all subsequent rounds. This
continues until no new source files are generated.
After a round occurs where no new source files are generated, the
annotation processors are called one last time, to give them a chance
to complete any remaining work. Finally, unless the -proc:only option
is used, the compiler compiles the original and all generated source
files.
IMPLICITLY LOADED SOURCE FILES
To compile a set of source files, the compiler might need to implicitly
load additional source files. See Searching for Types. Such files are
currently not subject to annotation processing. By default, the
compiler gives a warning when annotation processing occurred and any
implicitly loaded source files are compiled. The -implicit option
provides a way to suppress the warning.
SEARCHING FOR TYPES
To compile a source file, the compiler often needs information about a
type, but the type definition is not in the source files specified on
the command line. 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 that provide information through inheritance.
For example, when you create a subclass java.applet.Applet, you are
also using the ancestor classes of Applet: java.awt.Panel,
java.awt.Container, java.awt.Component, and java.lang.Object.
When the compiler needs type information, it searches for a source file
or class file that defines the type. The compiler searches for class
files 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 option.
If you set the -sourcepath option, then the compiler searches the
indicated path for source files. Otherwise, the compiler searches the
user class path for both class files and source files.
You can specify different bootstrap or extension classes with the
-bootclasspath and the -extdirs options. See Cross-Compilation Options.
A successful type search may produce a class file, a source file, or
both. If both are found, then you can use the -Xprefer option to
instruct the compiler which to use. If newer is specified, then the
compiler uses the newer of the two files. If source is specified, the
compiler uses the source file. The default is newer.
If a type search finds a source file for a required type, either by
itself, or as a result of the setting for the -Xprefer option, then the
compiler reads the source file to get the information it needs. By
default the compiler also compiles the source file. You can use the
-implicit option to specify the behavior. If none is specified, then no
class files are generated for the source file. If class is specified,
then class files are generated for the source file.
The compiler might not discover the need for some type information
until after annotation processing completes. When the type information
is found in a source file and no -implicit option is specified, the
compiler gives a warning that the file is being compiled without being
subject to annotation processing. To disable the warning, either
specify the file on the command line (so that it will be subject to
annotation processing) or use the -implicit option to specify whether
or not class files should be generated for such source files.
PROGRAMMATIC INTERFACE
The javac command supports the new Java Compiler API defined by the
classes and interfaces in the javax.tools package.
EXAMPLE
To compile as though providing command-line arguments, use the
following syntax:
JavaCompiler javac = ToolProvider.getSystemJavaCompiler();
The example writes diagnostics to the standard output stream and
returns the exit code that javac would give when called from the
command line.
You can use other methods in the javax.tools.JavaCompiler interface to
handle diagnostics, control where files are read from and written to,
and more.
OLD INTERFACE
Note: This API is retained for backward compatibility only. All new
code should use the newer Java Compiler API.
The com.sun.tools.javac.Main class provides two static methods to call
the compiler from a program:
public static int compile(String[] args);
public static int compile(String[] args, PrintWriter out);
The args parameter represents any of the command-line arguments that
would typically be passed to the compiler.
The out parameter indicates where the compiler diagnostic output is
directed.
The return value is equivalent to the exit value from javac.
Note: All other classes and methods found in a package with names that
start with com.sun.tools.javac (subpackages of com.sun.tools.javac) are
strictly internal and subject to change at any time.
EXAMPLES
Example 1 Compile a Simple Program
This example shows how to compile the Hello.java source file in the
greetings directory. The class defined in Hello.java is called
greetings.Hello. The greetings directory is the package directory both
for the source file and the class file and is underneath the current
directory. This makes it possible to use the default user class path.
It also makes it unnecessary to specify a separate destination
directory with the -d option.
The source code in 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]);
}
}
}
Compile greetings.Hello:
javac greetings/Hello.java
Run greetings.Hello:
java greetings.Hello World Universe Everyone
Hello World
Hello Universe
Hello Everyone
Example 2 Compile Multiple Source Files
This example compiles the Aloha.java, GutenTag.java, Hello.java, and
Hi.java source files in the greetings package.
% javac greetings/*.java
% ls greetings
Aloha.class GutenTag.class Hello.class Hi.class
Aloha.java GutenTag.java Hello.java Hi.java
Example 3 Specify a User Class Path
After changing one of the source files in the previous example,
recompile it:
pwd
/examples
javac greetings/Hi.java
Because greetings.Hi refers to other classes in the greetings package,
the compiler needs to find these other classes. The previous example
works because the default user class path is the directory that
contains the package directory. If you want to recompile this file
without concern for which directory you are in, then add the examples
directory to the user class path by setting CLASSPATH. This example
uses the -classpath option.
javac-classpath /examples /examples/greetings/Hi.java
If you change greetings.Hi to use a banner utility, then 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 the greetings package, the program needs access
to the greetings package, and to the classes that the greetings classes
use.
java -classpath /examples:/lib/Banners.jar greetings.Hi
Example 4 Separate Source Files and Class Files
The following example uses javac to compile code that runs on JVM 1.7.
javac-source 1.7 -target 1.7 -bootclasspath jdk1.7.0/lib/rt.jar \
-extdirs "" OldCode.java
The -source 1.7 option specifies that release 1.7 (or 7) of the Java
programming language be used to compile OldCode.java. The option
-target 1.7 option ensures that the generated class files are
compatible with JVM 1.7. Note that in most cases, the value of the
-target option is the value of the -source option; in this example, you
can omit the -target option.
You must specify the -bootclasspath option to specify the correct
version of the bootstrap classes (the rt.jar library). If not, then the
compiler generates a warning:
javac-source 1.7 OldCode.java
warning: [options] bootstrap class path not set in conjunction with
-source 1.7
If you do not specify the correct version of bootstrap classes, then
the compiler uses the old language rules (in this example, it uses
version 1.7 of the Java programming language) combined with the new
bootstrap classes, which can result in class files that do not work on
the older platform (in this case, Java SE 7) because reference to
nonexistent methods can get included.
Example 5 Cross Compile
This example uses javac to compile code that runs on JVM 1.7.
javac-source 1.7 -target 1.7 -bootclasspath jdk1.7.0/lib/rt.jar \
-extdirs "" OldCode.java
The-source 1.7 option specifies that release 1.7 (or 7) of the Java
programming language to be used to compile OldCode.java. The -target
1.7 option ensures that the generated class files are compatible with
JVM 1.7.
You must specify the -bootclasspath option to specify the correct
version of the bootstrap classes (the rt.jar library). If not, then the
compiler generates a warning:
javac-source 1.7 OldCode.java
warning: [options] bootstrap class path not set in conjunction with -source 1.7
If you do not specify the correct version of bootstrap classes, then
the compiler uses the old language rules combined with the new
bootstrap classes. This combination can result in class files that do
not work on the older platform (in this case, Java SE 7) because
reference to nonexistent methods can get included. In this example, the
compiler uses release 1.7 of the Java programming language.
SEE ALSO
· java(1)
· jdb(1)
· javah(1)
· javadoc(1)
· jar(1)
· jdb(1)JDK 8 03 March 2015 javac(1)
