javac-java-1.6.0-openjdk (1) - Linux Manuals
javac-java-1.6.0-openjdk: Java programming language compiler
NAME
javac - Java programming language compiler
SYNOPSIS
javac [ options ] [ sourcefiles ] [ @argfiles ]
Arguments may be in any order.
-
-
- options
- Command-line options.
- sourcefiles
- One or more source files to be compiled (such as MyClass.java).
- @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.
There are two ways to pass source code filenames 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 file in the same directory as its source file. You can specify a separate destination directory with -d (see Options, below).
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 file which 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 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. Here is how javac handles each situation:
-
- o
- Search produces a class file but no source file: javac uses the class file.
- o
- Search produces a source file but no class file: javac compiles the source file and uses the resulting class file.
- o
- Search produces both a source file and a class file: javac determines whether the class file is out of date. If the class file is out of date, javac recompiles the source file and uses the updated class file. Otherwise, javac just uses the class file.
javac considers a class file out of date only if it is older than the source file.
Note:
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.
If the -sourcepath option is not specified, the user class path is searched for both source files and class files.
As a special convenience, a class path element containing a basename of * is considered equivalent to specifying a list of all the files in the directory with the extension .jar or .JAR (a java program cannot tell the difference between the two invocations).
If -d is not specified, javac puts the class file in the same directory as the source file.
Note:
Note:
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 -bootclasspath and -extdirs when cross-compiling; see Cross-Compilation Example below.
The default for -target depends on the value of -source:
Note:
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 newline-separated. If a filename contains embedded spaces, put the whole filename in double quotes.
Filenames within an argument file are relative to the current directory, not the location of the argument file. Wildcards (*) are not allowed in these lists (such as for specifying *.java). Use of the '@' character to recursively interpret files is not supported. 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.
You could use a single argument file named "argfile" to hold all javac arguments:
This argument file could contain the contents of both files shown in the next example.
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:
Create a file named "classes" containing:
You would then run javac with:
The argument files can have paths, but any filenames inside the files are relative to the current working directory (not path1 or path2):
The com.sun.tools.javac.Main class provides two static methods to invoke the compiler from a program:
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.
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.
This example compiles all the source files in the package greetings.
Having changed one of the source files in the previous example, we recompile it:
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.
If we change greetings.Hi again, to use a banner utility, that utility also needs to be accessible through the user class path.
To execute a class in greetings, we need access both to greetings and to the classes it uses.
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.
Note:
Here we use javac to compile code that will run on a 1.4 VM.
The -target 1.4 option ensures that the generated class files will be compatible with 1.4 VMs. By default, javac compiles for JDK 6.
The Java Platform JDK's javac would also by default compile against its own bootstrap classes, so we need to tell javac to compile against JDK 1.4 bootstrap classes instead. We do this with -bootclasspath and -extdirs. Failing to do this might allow compilation against a Java Platform API that would not be present on a 1.4 VM and would fail at runtime.
OPTIONS
Standard Options
For example, if directory foo contains a.jar and b.JAR, then the class path element foo/* is expanded to a A.jar:b.JAR, except that the order of jar files is unspecified. All jar files in the specified directory, even hidden ones, are included in the list. A classpath entry consisting simply of * expands to a list of all the jar files in the current directory. The CLASSPATH environment variable, where defined, will be similarly expanded. Any classpath wildcard expansion occurs before the Java virtual machine is started -- no Java program will ever see unexpanded wildcards except by querying the environment. For example; by invoking System.getenv("CLASSPATH").
Note: No language changes were introduced in JDK 6, so the values 1.6 and 6 are not valid.
Cross-Compilation Options
Non-Standard Options
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 case in question.
switch (x) {
case 1:
System.out.println("1");
// No break; statement here.
case 2:
System.out.println("2");
}
The -J Option
COMMAND LINE ARGUMENT FILES
Example - Single Arg File
C:> javac @argfile
Example - Two Arg Files
-d classes
-g
-sourcepath \java\pubs\ws\1.3\src\share\classes
MyClass1.java
MyClass2.java
MyClass3.java
% javac @options @classes
Example - Arg Files with Paths
% javac @path1/options @path2/classes
PROGRAMMATIC INTERFACE
public static int compile(String[] args);
public static int compile(String[] args, PrintWriter out);
EXAMPLES
Compiling a Simple Program
% 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
% 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
% pwd
/examples
% javac greetings/Hi.java
% javac -classpath /examples /examples/greetings/Hi.java
% javac -classpath /examples:/lib/Banners.jar \
/examples/greetings/Hi.java
% java -classpath /examples:/lib/Banners.jar greetings.Hi
Separating Source Files and Class Files
% 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
Cross-Compilation Example
% javac -target 1.4 -bootclasspath jdk1.4.2/lib/classes.zip \
-extdirs "" OldCode.java
SEE ALSO