「javac」

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javac,读取Java类和接口定义,并将其编译为bytecode和.class文件。

命令行语法格式(SYNOPSIS)

javac [ 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.

命令简述(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.

命令支持的选项及含义(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
生成所有debug信息,包括局部变量。默认情况下,只生成行号和源文件信息。

-g:none
不生成任何debug信息。

-g:[keyword list]
只生成某些debug信息。多个keyword之间使用逗号分隔。
keyword的取值:source(源码文件的debug信息)、lines(行号的debug信息)、vars(本地变量的debug信息)

-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)

参考文献