javac [ options ] [ sourcefiles ] [ classes] [ @argfiles ]
Arguments can be in any order:
There are two ways to pass source code file names to javac.
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.
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.
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.
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.
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.
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.
Note: Classes found through the class path might be recompiled when their source files are also found. See Searching for Types.
The default for the -target option depends on the value of the -source option:
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.
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.
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
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.
String s = (String) "Hello!"
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
/**
* @deprecated As of Java SE 7, replaced by {@link #newMethod()}
*/
public static void deprecatedMethood() { }
public static void newMethod() { }
int divideByZero = 42 / 0;
class E {
void m() {
if (true) ;
}
}
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.
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.
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.
javac -Xlint:path -classpath /nonexistentpath Example.java
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.
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.
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.
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 ( AutoCloseable ac = getResource() ) { // do nothing}
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.
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.
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
The API for annotation processors is defined in the javax.annotation.processing and javax.lang.model packages and subpackages.
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.
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.
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.
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.
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.