>man javac
Name
javac - Java programming language compiler
SYNOPSIS
javac [ options ] [ sourcefiles ] [ classes ] [ @argfiles ]
Arguments may be in any order.
options
Command-line 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 lists options and source files. The -J
options are not allowed in these files.
DESCRIPTION
The javac tool reads class and interface definitions, written in the
Java programming language, and compiles them into bytecode class files.
It can also process annotations in Java source files and classes.
There are two ways to pass source code file names to javac:
o For a small number of source files, simply list the file names on
the command line.
o For a large number of source files, list 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 filein the same directory as
its source file. You can specify a separate destination directory with
-d (see Options, below).
OPTIONS
The compiler has a set of standard options that are supported on the
current development environment and will be supported in future
releases. An additional set of non-standard options are specific to the
current virtual machine and compiler implementations and are subject to
change in the future. Non-standard options begin with -X.
Standard Options
-Akey[=value]
Options to pass to annotation processors. These are not inter-
preted by javac directly, but are made available for use by indi-
vidual processors. key should be one or more identifiers sepa-
rated by ".".
-cp path or -classpath path
Specify where to find user class files, and (optionally) annota-
tion 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, the user class path
consists of the current directory. See Setting the Class Path formore details.
>If the -sourcepath option is not specified, the user class path
is also searched for source files.
If the -processorpath option is not specified, the class path is
also searched for annotation processors.
-Djava.ext.dirs=directories
Override the location of installed extensions.
-Djava.endorsed.dirs=directories
Override the location of endorsed standards path.
-d directory
Set the destination directory for class files. The directory must
already exist; javac will not create it. If a class is part of a
package, javac puts the class filein 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 each class files in the same
directory as the source file from which it was generated.
Note: The directory specified by -d is not automatically added to
your user class path.
-deprecation
Show a description of each use or override of a deprecated member
or class. Without -deprecation, javac shows a summary of the
source files that use or override deprecated members or classes.
-deprecation is shorthand for -Xlint:deprecation.
-encoding encoding
Set the source file encoding name, such as EUC-JP and UTF-8. If
-encoding is not specified, the platform default converter is
used.
-endorseddirs directories
Override the location of endorsed standards path.
-extdirs directories
Overrides the location of the ext directory. The directories
variable is a colon-separated list of directories. Each JAR ar-
chive in the specified directories is searched for class files.
All JAR archives found are automatically part of the class path.
If you are cross-compiling (compiling classes against bootstrap
and extension classes of a different Java platform implementa-
tion), this option specifies the directories that contain the
extension classes. See Cross-Compilation Options formore infor-
mation.
-g Generate all debugging information, including local variables. By
default, only line number and source file information is gener-
ated.
-g:none
Do not generate any debugging information.
-g:{keyword list}
Generate 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
Print 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, the default is
to automatically generate class files. In this case, the compiler
will issue a warning if any such class files are generated when
also doing annotation processing. The warning will not be issued
if this option is set explicitly. See Searching For Types.
-Joption
Pass option to the java launcher called by javac. For example,
-J-Xms48m sets the startup memory to 48 megabytes. It is a common
convention for -J to pass options to the underlying VM executing
applications written in Java.
Note: CLASSPATH, -classpath, -bootclasspath, and -extdirs do not
specify the classes used to run javac. Fiddling with the imple-
mentation 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.
-nowarn
Disable warning messages. This has the same meaning as
-Xlint:none.
-proc: {none,only}
Controls whether annotation processing and/or compilation is
done. -proc:none means that compilation takes place without anno-
tation processing. -proc:only means that only annotation process-
ing 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
Specify where to find annotation processors; if this option is
not used, the class path will be searched for processors.
-s dir
Specify the directory where to place generated source files. The
directory must already exist; javac will not create it. If a
class is part of a package, the compiler puts the source filein
a subdirectory reflecting the package name, creating directories
as needed. For example, if you specify -s /home/mysrc and the
class is called com.mypackage.MyClass, then the source file will
be placed in /home/mysrc/com/mypackage/MyClass.java.
-source release
Specifies the version of source code accepted. The following val-
ues 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 lan-
guage features introduced in Java SE 5.
5 Synonym for1.5.
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 previous releases of Java SE.
6 Synonym for1.6.
1.7
This is the default value. The compiler accepts code with fea-
tures introduced in Java SE 7.
7 Synonym for1.7.
-sourcepath sourcepath
Specify 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: Classes found through the class path may be subject to
automatic recompilation if their sources are also found. See
Searching For Types.
-verbose
Verbose output. This includes information about each class loaded
and each source file compiled.
-version
Print version information.
-Werror
Terminate compilation if warnings occur.
-X Display information about non-standard options and exit.
Cross-Compilation Options
By default, classes are compiled against the bootstrap and extension
classes of the platform that javac shipped with. But javac also sup-
ports cross-compiling, where classes are compiled against a bootstrap
and extension classes of a different Java platform implementation. It
is important to use -bootclasspath and -extdirs when cross-compiling;
see Cross-Compilation Example below.
-target version
Generate class files that target a specified version of the VM.
Class files will run on the specified target and on later ver-
sions, but not on earlier versions of the VM. Valid targets are
1.1, 1.2, 1.3, 1.4, 1.5 (also 5), 1.6 (also 6), and 1.7 (also 7).
The default for -target depends on the value of -source:
o If -source is not specified, the value of -target is 1.7
o If -source is 1.2, the value of -target is 1.4
o If -source is 1.3, the value of -target is 1.4
o If -source is 1.5, the value of -target is 1.7
o If -source is 1.6, the value of -target is 1.7
o For all other values of -source, the value of -target is the
value of -source.
-bootclasspath bootclasspath
Cross-compile 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.
Non-Standard Options
-Xbootclasspath/p:path
Prepend to the bootstrap class path.
-Xbootclasspath/a:path
Append to the bootstrap class path.
-Xbootclasspath/:path
Override location of bootstrap class files.
-Xlint
Enable all recommended warnings. In this release, enabling all
available warnings is recommended.
-Xlint:all
Enable all recommended warnings. In this release, enabling all
available warnings is recommended.
-Xlint:none
Disable all warnings.
-Xlint:name
Enable warning name. See the section Warnings That Can Be Enabled
or Disabled with -Xlint Option for a list of warnings you can
enable with this option.
-Xlint:-name
Disable warning name. See the section Warnings That Can Be
Enabled or Disabled with -Xlint Option for a list of warnings you
can disable with this option.
-Xmaxerrs number
Set the maximum number of errors to print.
-Xmaxwarns number
Set the maximum number of warnings to print.
-Xstdout filename
Send compiler messages to the named file. By default, compiler
messages go to System.err.
-Xprefer:{newer,source}
Specify whichfile to read when both a source file and class file
are found for a type. (See Searching For Types). If -Xpre-
fer:newer is used, it reads the newer of the source or class filefor a type (default). If the -Xprefer:source option is used, it
reads 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}
Specify handling of package-info files
-Xprint
Print out textual representation of specified types for debugging
purposes; perform neither annotation processing nor compilation.
The format of the output may change.
-XprintProcessorInfo
Print information about which annotations a processor is asked to
process.
-XprintRounds
Print information about initial and subsequent annotation pro-
cessing rounds.
Warnings That Can Be Enabled or Disabled with -Xlint Option
Enable warning name with the option -Xlint:name, where name is one of
the following warning names. Similarly, you can disable warning name
with the option -Xlint:-name:
cast
Warn about unnecessary and redundant casts. For example:
String s = (String)"Hello!"
classfile
Warn about issues related to classfile contents.
deprecation
Warn about 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
Warn 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
Warn about division by constant integer 0. For example:
int divideByZero = 42 / 0;
empty
Warn about empty statements after if statements. For example:
class E {
void m() {
if (true) ;
}
}
fallthrough
Check switch blocks for fall-through cases and provide a warning
message for any that are found. Fall-through cases are cases in a
switch block, other than the lastcasein 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 case1 label in this switch block does not end
with a break statement:
switch (x) {
case1:
System.out.println("1");
// No break statement here.case2:
System.out.println("2");
}
If the -Xlint:fallthrough 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 casein question.
finally
Warn about finally clauses that cannot complete normally. For
example:
public static int m() {
try {
throw new NullPointerException();
} catch (NullPointerException e) {
System.err.println("Caught NullPointerException.");
return 1;
} finally {
return 0;
}
}
The compiler generates a warning for finally block in this exam-
ple. When this method is called, it returns a value of 0, not 1.
A finally block always executes when the try block exits. In this
example, if control is transferred to the catch, then the method
exits. However, the finally block must be executed, so it is exe-
cuted, even though control has already been transferred outside
the method.
options
Warn about issues relating to the use of command line options.
See Cross-Compilation Example for an example of this kind of
warning.
overrides
Warn about issues regarding method overrides. For example, con-
sider 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 ClassWithOverrid-
ingMethod overrides varargsMethod(String...) in ClassWith-
VarargsMethod; overriding method is missing '...'
When the compiler encounters a varargs method, it translates the
varargs formal parameter into an array. In the method ClassWith-
VarargsMethod.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 Class-
WithOverridingMethod.varargsMethod. Consequently, this example
compiles.
path
Warn about invalid path elements and nonexistent path directories
on the command line (with regards 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 if you have a class that has an annota-
tion, and you use an annotation processor that cannot handle that
type of exception. For example, the following is a simple annota-
tion processor:
Source file AnnoProc.java:
import java.util.*;
import javax.annotation.processing.*;
import javax.lang.model.*;
import javax.lang.model.element.*;
@SupportedAnnotationTypes("NotAnno")
public class AnnoProc extends AbstractProcessor {
public boolean process(Set 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 follow-
ing warning:
warning: [processing] No processor claimed any of these annota-
tions: Anno
To resolve this issue, you can rename the annotation defined and
used in the class AnnosWithoutProcessors from Anno to NotAnno.
rawtypes
Warn about unchecked operations on raw types. The following
statement generates a rawtypes warning:
void countElements(List l) { ... }
The following does not generate a rawtypes warning:
void countElements(List l) { ... }
List is a raw type. However, List is a unbounded wildcard
parameterized type. Because List is a parameterized interface,
you should always specify its type argument. In this example, the
List formal argument is specified with a unbounded wildcard (?)
as its formal type parameter, which means that the countElements
method can accept any instantiation of the List interface.
serial
Warn 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 defi-
nition of serialVersionUID
If a serializable class does not explicitly declare a field named
serialVersionUID, then the serialization runtime will calculate a
default serialVersionUID value for that class based on various
aspects of the class, as described in the Java Object Serializa-
tion 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 may vary depending on
compiler implementations, and can thus result in unexpected
InvalidClassExceptions during deserialization. Therefore, to
guarantee a consistent serialVersionUID value across different
Java compiler implementations, a serializable class must declare
an explicit serialVersionUID value.
static
Warn about issues relating to 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 fol-
lows:
XLintStatic.m1();
Alternatively, you can remove the static keyword from the decla-
ration of the method m1.
try
Warn about issues relating to use of try blocks, including
try-with-resources statements. For example, a warning is gener-
ated for the following statement because the resource ac declared
in the try statement is not used:
try ( AutoCloseable ac = getResource() ) {
// do nothing }
unchecked
Give more detail for unchecked conversion warnings that are man-
dated by the Java Language Specification. For example:
List l = new ArrayList();
Listls = l; // unchecked warning
During type erasure, the types ArrayList and List
become ArrayList and List, respectively.
The variable ls has the parameterized type List. When the
List referenced by l is assigned to ls, the compiler generates an
unchecked warning; the compiler is unable to determine at compile
time, and moreover knows that the JVM will not be able to deter-
mine at runtime, if l refers to a List type; it does not.
Consequently, heap pollution occurs.
In detail, a heap pollution situation occurs when the List object
l, whose static type is List, is assigned to another List
object, ls, that has a different static type, List. How-
ever, the compiler still allows this assignment. It must allow
this assignment to preserve backwards compatibility with versions
of Java SE that do not support generics. Because of type erasure,
List and List both become List. Consequently, the
compiler allows the assignment of the object l, which has a raw
type of List, to the objectls.
varargs
Warn about unsafe usages of variable arguments (varargs) methods,
in particular, those that contain non-reifiable arguments. For
example:
public class ArrayBuilder {
public static void addToList (List listArg, T... elements) {
for (T x : elements) {
listArg.add(x);
}
}
}
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 pro-
gramming 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 line, you can specify one or
more files that themselves 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 filenames in any
combination. The arguments within a file can be space-separated or new-
line-separated. If a filename contains embedded spaces, put the whole
filename indouble quotes.
Filenames within an argument file are relative to the current direc-
tory, 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. The -J
options are not supported because they are passed to the launcher,
which does not support argument files.
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
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
the next example.
Example - Two Arg Files
You can create two argument files -- one for the javac options and the
other for the source filenames: (Notice the following lists have no
line-continuation characters.)
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:
% javac @options @classes
Example - Arg Files with Paths
The argument files can have paths, but any filenames inside the files
are relative to the current working directory (not path1 or path2):
% javac @path1/options @path2/classes
ANNOTATION PROCESSING
javac provides direct support for annotation processing, superseding
the need for the separate annotation processing tool, apt.
The API for annotation processors is defined in the javax.annota-
tion.processing and javax.lang.model packages and subpackages.
Overview of annotation processing
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 it
is not given, the user class path is used. Processors are located by
means of service provider-configuration files named META-INF/ser-
vices/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 explic-
itly, 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 pro-
cessors to determine what annotations they process. When a match is
found, the processor will be invoked. A processor may "claim" the anno-
tations it processes, inwhichcase no further attempt is made to find
any processors for those annotations. Once all annotations have been
claimed, the compiler does not look for additional processors.
If any processors generate any new source files, another round of anno-
tation processing will occur: any newly generated source files will be
scanned, and the annotations processed as before. Any processors
invoked on previous rounds will also be invoked 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 anno-
tation processors will be invoked one lasttime, to give them a chance
to complete any work they may need to do. Finally, unless the
-proc:only option is used, the compiler will compile the original and
all the generated source files.
Implicitly loaded source files
To compile a set of source files, the compiler may need to implicitly
load additional source files. (See Searching For Types). Such files are
currently not subject to annotation processing. By default, the com-
piler will give a warning if annotation processing has occurred and any
implicitly loaded source files are compiled. See the -implicit option
for ways to suppress the warning.
SEARCHING FOR TYPES
When compiling a source file, the compiler often needs information
about a type whose definition did not appear in the source files given
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 which provide information through inheritance.
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.lang.Object.
When the compiler needs type information, it looks for a source file or
class filewhich defines the type. The compiler searches for class
files first in the bootstrap and extension classes, thenin the user
class path (which by default is the current directory). The user class
path is defined by setting the CLASSPATH environment variable or by
using the -classpath command line option. (For details, see Setting the
Class Path).
If you set the -sourcepath option, 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 -extdirs options; see Cross-Compilation Options
below.
A successful type search may produce a class file, a source file, or
both. If both are found, you can use the -Xprefer option to instruct
the compiler which to use. If newer is given, the compiler will use the
newer of the two files. If source is given, it will use the source
file. The default is newer.
If a type search finds a source filefor a required type, either by
itself, or as a result of the setting for -Xprefer, the compiler will
read the source file to get the information it needs. In addition, it
will by default compile the source file as well. You can use the
-implicit option to specify the behavior. If none is given, no class
files will be generated for the source file. If class is given, class
files will be generated for the source file.
The compiler may not discover the need for some type information until
after annotation processing is complete. If the type information is
found in a source file and no -implicit option is given, the compiler
will give a warning that the file is being compiled without being sub-
ject 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
javac supports the new Java Compiler API defined by the classes and
interfaces in the javax.tools package.
Example
To perform a compilation using arguments as you would give on the com-
mand line, you can use the following:
JavaCompiler javac = ToolProvider.getSystemJavaCompiler();
int rc = javac.run(null, null, null, args);
This will write any diagnostics to the standard output stream, and
return the exit code that javac would give when invoked from the com-
mand line.
You can use other methods on the javax.tools.JavaCompiler interface to
handle diagnostics, control where files are read from and written to,
and so on.
Old Interface
Note: This API is retained for backwards compatibility only; all new
code should use the Java Compiler API, described above.
The com.sun.tools.javac.Main class provides two static methods to
invoke 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 normally be passed to the javac program and are outlined in the
above Synopsis section.
The out parameter indicates where the compiler's diagnostic output is directed.
The return value is equivalent to the exit value from javac.
Note that all other classes and methods found in a package whose name
starts with com.sun.tools.javac (informally known as sub-packages of
com.sun.tools.javac) are strictly internal and subject to change at any
time.
EXAMPLES
Compiling a Simple Program
One source file, Hello.java, defines a class called greetings.Hello.
The greetings directory is the package directory both for the source
file and the class file and is off the current directory. This allows
us to use the default user class path. It also makes it unnecessary to
specify a separate destination directory with -d.
% ls
greetings/
% ls greetings
Hello.java
% cat greetings/Hello.java
package greetings;
public class Hello {
public static void main(String[] args) {
for (int i=0; i < args.length; i++) {
System.out.println("Hello " + args[i]);
}
}
}
% javac greetings/Hello.java
% ls greetings
Hello.class Hello.java
% java greetings.Hello World Universe Everyone
Hello World
Hello Universe
Hello Everyone
Compiling Multiple Source Files
This example compiles all the source files in the package greetings.
% ls
greetings/
% ls greetings
Aloha.java GutenTag.java Hello.java Hi.java
% javac greetings/*.java
% ls greetings
Aloha.class GutenTag.class Hello.class Hi.class
Aloha.java GutenTag.java Hello.java Hi.java
Specifying a User Class Path
Having changed one of the source files in the previous example, we
recompile it:
% pwd
/examples
% javac greetings/Hi.java
Since greetings.Hi refers to other classes in the greetings package,
the compiler needs to find these other classes. The example above
works, because our default user class path happens to be the directory
containing the package directory. But suppose we want to recompile this
file and not worry about which directory we're in? Then we need to add
/examples to the user class path. We can do this by setting CLASSPATH,
but here we'll use the -classpath option.
% javac -classpath /examples /examples/greetings/Hi.java
If we change greetings.Hi again, to use a banner utility, that utility
also needs to be accessible through the user class path.
% javac -classpath /examples:/lib/Banners.jar \
/examples/greetings/Hi.java
To execute a class in greetings, we need access both to greetings and
to the classes it uses.
% java -classpath /examples:/lib/Banners.jar greetings.Hi
Separating Source Files and Class Files
It often makes sense to keep source files and class files in separate
directories, especially on large projects. We use -d to indicate the
separate class file destination. Since the source files are not in the
user class path, we use -sourcepath to help the compiler find them.
% ls
classes/ lib/ src/
% ls src
farewells/
% ls src/farewells
Base.java GoodBye.java
% ls lib
Banners.jar
% ls classes
% javac -sourcepath src -classpath classes:lib/Banners.jar \
src/farewells/GoodBye.java -d classes
% ls classes
farewells/
% ls classes/farewells
Base.class GoodBye.class
Note: The compiler compiled src/farewells/Base.java, even though we
didn't specify it on the command line. To trace automatic compiles, use
the -verbose option.
Cross-Compilation Example
The following example uses javac to compile code that will run on a 1.6
VM.
% javac -source 1.6 -target 1.6 -bootclasspath jdk1.6.0/lib/rt.jar \
-extdirs "" OldCode.java
The -source 1.6 option specifies that version 1.6 (or 6) of the Java
programming language be used to compile OldCode.java. The option -tar-
get 1.6 option ensures that the generated class files will be compati-
ble with 1.6 VMs. 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 ver-
sion of the bootstrap classes (the rt.jar library). If not, the com-
piler generates a warning:
% javac -source 1.6 OldCode.java
warning: [options] bootstrap class path not set in conjunction with -source 1.6
If you do not specify the correct version of bootstrap classes, the
compiler will use the old language rules (in this example, it will use
version 1.6 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 6) because reference to
non-existent methods can get included.
SEE ALSO
o The javac Guide @
http://docs.oracle.com/javase/7/docs/tech-
notes/guides/javac/index.html
o java(1) - the Java Application Launcher
o jdb(1) - Java Application Debugger
o javah(1) - C Header and Stub File Generator
o javap(1) - Class File Disassembler
o javadoc(1) - API Documentation Generator
o jar(1) - JAR Archive Tool
o The Java Extensions Framework @
http://docs.oracle.com/javase/7/docs/technotes/guides/exten-
sions/index.html
Tomcat的组成部分 1、server
A Server element represents the entire Catalina servlet container. (Singleton) 2、service
service包括多个connector以及一个engine，其职责为处理由connector获得的客户请求。
3、connector
一个connector
基本概念: 1.OOP中唯一关系的是对象的接口是什么,就像计算机的销售商她不管电源内部结构是怎样的,他只关系能否给你提供电就行了,也就是只要知道can or not而不是how and why.所有的程序是由一定的属性和行为对象组成的,不同的对象的访问通过函数调用来完成,对象间所有的交流都是通过方法调用,通过对封装对象数据,很大限度上提高复用率。 2.OOP中最重要的思想是类,类是模板是蓝图,
由于明天举要上课,所以刚刚将代码敲了一遍PL/SQL的函数和包体的实现(单例模式过几天好好的总结下再发出来);以便明天能更好的学习PL/SQL的循环,今天太累了,所以早点睡觉,明天继续PL/SQL总有一天我会将你永远的记载在心里,,,
函数;
函数:PL/SQL中的函数相当于java中的方法;函数有返回值
定义函数的
--输入姓名找到该姓名的年薪
create or re
/*
*编写控制结构
*/
--条件分支语句
--简单条件判断
DECLARE
v_sal NUMBER(6,2);
BEGIN
select sal into v_sal from emp
where lower(ename)=lower('&name');
if v_sal<2000 then
update emp set
public class CollectionDemo implements Serializable,Comparable<CollectionDemo>{
private static final long serialVersionUID = -2958090810811192128L;
private int id;
private String nam
