javap

Name

javap---The Java Class Disassembler

Availability

JDK 1.0 and later.

Synopsis

javap [ options ] classnames

Description

javap disassembles the class files specified by the class names on the command line and prints a human-readable version of those classes.

By default, javap prints declarations of the non-private members of each of the classes specified on the command line. The -l, -p, and -c options specify additional information to be printed, including a complete disassembly of the byte-codes in each of the specified classes. javap can also be used to run the class verifier on Java classes.

Options

-c

Print the Java Virtual Machine instructions for each of the methods in each of the specified classes. This option disassembles all methods, including private methods.

-classpath path

The path that javap uses to look up the classes named on the command line. This option overrides the default path and any path specified by the CLASSPATH environment variable. The path specified is an ordered list of directories and ZIP files, separated by colons on UNIX systems or semicolons on Windows systems.

To specify additional directories or ZIP files for javap to search without overriding the default system class path, use the CLASSPATH environment variable. See the java reference page for more information on specifying paths.

-h

Outputs the class in a form suitable for inclusion in a C header file.

-l

Prints line numbers and local variable tables in addition to the public fields of the class. Note that line numbers and local variable information is included for use with debuggers. Local variable information is available only if a class was compiled with the -g option to javac; line number information is available only if a class was compiled without the -O option.

-p

Prints private methods and variables of the specified class in addition to the public ones. Note that some compilers (though not javac) may allow this private field information to be "obfuscated" in such a way that private fields and method arguments no longer have meaningful names. This makes Java classes harder to disassemble or reverse engineer.

-s

Outputs the class member declarations using the internal Virtual Machine format.

-v

Verbose. Outputs additional information (in the form of Java comments) about each member of each specified class.

-verify

Causes javap to run the class verifier on the specified classes and display the results of verification.

-version

Causes javap to display its version number.

Environment

CLASSPATH

Specifies an ordered list (colon-separated on UNIX, semicolon-separated on Windows systems) of directories and ZIP files in which javap should look for class definitions. When a path is specified with this environment variable, javap always implicitly appends the location of the system classes to the end of the path. If this environment variable is not specified, the default path is the current directory and the system classes. This variable is overridden by the -classpath option.

javac

Name

javac---The Java Compiler

Availability

JDK 1.0 and later.

Synopsis

javac [ options ] files

Description

javac is the Java compiler--it compiles Java source code (in .java files) into Java byte-codes (in .class files). The Java compiler is itself written in Java.

javac may be passed any number of Java source files, whose names must all end with the .java extension. javac produces a separate .class class file for each class defined in the source files, regardless of how many source files there are. In other words, there need not be a one-to-one mapping between Java source files and Java class files. Note also that the compiler requires that there be only a single public class defined in any one source file, and that the name of the file (minus the .java extension) be the same as the name of the class (minus its package name, of course).

By default, javac places the class files it generates in the same directory as the corresponding source file. You can override this behavior with the -d option.

When a source file references a class that is not defined in another source file on the command line, javac searches for the definition of that class using the class path. The default class path contains only the current directory and the system classes. You may specify additional classes and packages to be searched with the -classpath option or the CLASSPATH environment variable.

If javac compiles a source file that relies on a class that is out of date (i.e., if the source file for that class is newer than the class file), it automatically recompiles that file.

Options

-classpath path

The path that javac uses to look up classes referenced in the specified source code. This option overrides the default path and any path specified by the CLASSPATH environment variable. The path specified is an ordered list of directories and ZIP files, separated by colons on UNIX systems or semicolons on Windows systems.

To specify additional directories or ZIP files to be searched, without overriding the default system class path, use the CLASSPATH environment variable. See the java reference page for more information on specifying paths.

-d directory

The directory in which (or beneath which) class files should be stored. By default, javac stores the .class files it generates in the same directory as the .java file that those classes were defined in. If the -d flag is specified, however, the specified directory is treated as the root of the class hierarchy and .class files are placed in this directory, or in the appropriate subdirectory below it, depending on the package name of the class. Thus, the following command:

% javac -d java/classes java/src/Checkers.java

places the file Checkers.class in the directory java/classes if the Checkers.java file has no package statement. On the other hand, if the source file specifies that it is in a package:

package david.games;

then the .class file is stored in java/classes/david/games. When the -d option is specified, javac automatically creates any directories it needs to store its class files in the appropriate place.

-depend

Tells javac to recompile any out-of-date class files it encounters, not just those that are referenced from one of the specified source files.

-deprecation

Tells javac to issue a warning for every use of a deprecated API. By default, javac issues only a single warning if a program uses deprecated APIs. Available in JDK 1.1 and later.

-g

This option tells javac to add line numbers and local variable information to the output class files, for use by debuggers. By default, javac only generates the line numbers. With the -O option, javac does not generate even that information.

-Jjavaoption

Pass the argument javaoption directly through to the Java interpreter. javaoption should not contain spaces; if multiple arguments must be passed to the interpreter, use multiple -J options. Available in JDK 1.1 and later.

-nowarn

Tells javac not to print warning messages. Errors are still reported as usual.

-nowrite

Tells javac not to create any class files. Source files are parsed as usual, but no output is written. This option is useful when you want to check that a file will compile without actually compiling it.

-O

Enable optimization of class files. This option may cause javac to compile static, final, and private methods inline, so that they execute faster. The trade-off is that the class files will be larger. This option also prevents javac from adding line number debugging information to the class files.

-verbose

Tells the compiler to display messages about what it is doing.

Environment

CLASSPATH

Specifies an ordered list (colon-separated on UNIX, semicolon-separated on Windows systems) of directories and ZIP files in which javac should look for class definitions. When a path is specified with this environment variable, javac always implicitly appends the location of the system classes to the end of the path. If this environment variable is not specified, the default path is the current directory and the system classes. This variable is overridden by the -classpath option.

java

Name

java---The Java Interpreter

Availability

JDK 1.0 and later.

Synopsis

java [ interpreter options ] classname [ program arguments ]java_g [ interpreter options ] classname [ program arguments ]

Description

java is the Java byte-code interpreter--it runs Java programs. java_g is a debugging version of the interpreter. It is unoptimized, and has some additional options for tracing the execution of a program.

The program to be run is the class specified by classname. This must be a fully qualified name, it must include the package name of the class, but not the .class file

extension. Note that you specify the package and class name, with components separated by '.', not the directory and filename of the class, which has its components separated by '/' or '/'. If a Java class has no package statement, then it is not in any package, and the class name is specified alone. Examples:

% java david.games.Checkers% java test

See the description of the -classpath option and the CLASSPATH environment variable below for information on specifying where java should look for classes.

The class specified by classname must contain a method main() with exactly the following signature:

public static void main(String argv[])

Any arguments following the classname on the java command line are placed into an array and passed to the main() method when java starts up.

If main() creates any threads, java runs until the last thread exits. Otherwise, the interpreter executes the body of main() and exits.

Although only a single class name is specified when invoking java, the interpreter automatically loads any additional classes required by the program. These classes are located relative to the Java class path, described under the -classpath option below.

By default, java runs a byte-code verifier on all classes loaded over the network. This verifier performs a number of tests on the byte-code of the loaded class to ensure, for example, that it does not corrupt the internal operand stack and that it performs appropriate run-time checks on such things as array references. The -verify, -noverify, and -verifyremote options control the byte-code verification process.

Options

-classpath path

The path that java uses to look up the specified classname and all other classes that it loads. Specifying this option overrides the default path and the CLASSPATH environment variable. The class path is an ordered list of directories and ZIP files within and below which java searches for named classes. On UNIX systems, a path is specified as a colon-separated list of directories and ZIP files. On Windows systems, directories and ZIP files (which may have drive specifiers that use colons) are separated from each other with semicolons. For example, a UNIX -classpath specification might look like this:

-classpath /usr/lib/java/classes:.:~/java/classes

On a Windows system, the specification might be:

-classpath C:\tools\java\classes.zip;.;D:\users\david\classes

A period by itself in the path indicates that the current working directory is searched. Directories and ZIP files are searched in the order they appear. Place the standard Java classes first in the path if you do not want them to be accidentally or maliciously overridden by classes with the same name in other directories.

java expects to find class files in a directory hierarchy (or with a directory name within a ZIP file) that maps to the fully qualified name of the class. Thus, on a UNIX system, Java would load the class java.lang.String by looking for the file java/lang/String.class beneath one of the directories specified in the class path. Similarly, on a Windows 95 or Windows NT system (which support long filenames), java would look for the file java\lang\String.class beneath a specified directory or within a specified ZIP file.

If you do not specify -classpath or the CLASSPATH environment variable, the default class path is:

.:$JAVA/classes:$JAVA/lib/classes.zip UNIX systems

.;$JAVA\classes;$JAVA\lib\classes.zip Windows systems

Where $JAVA is JDK installation directory.

-cs, -checksource

Both of these options tell java to check the modification times on the specified class file and its corresponding source file. If the class file cannot be found or if it is out of date, it is automatically recompiled from the source.

-Dpropertyname=value

Defines propertyname to equal value in the system properties list. Your Java program can then look up the specified value by its property name. You may specify any number of -D options. For example:

% java -Dawt.button.color=gray -Dmy.class.pointsize=14 my.class-debug

Causes java to display a password as it starts up. This password can be used to allow the jdb debugger to attach itself to this interpreter session. Note that this password should not be considered cryptographically secure.

-help

Print a usage message and exit.

-ldigit

Sets the logging level for trace output. java_g only.

-ms initmem[k|m]

Specifies how much memory is allocated for the heap when the interpreter starts up. By default, initmem is specified in bytes. You can specify it in kilobytes by appending the letter k or in megabytes by appending the letter m. The default is 1 MB. For large or memory intensive applications (such as the Java compiler), you can improve run-time performance by starting the interpreter with a larger amount of memory. You must specify an initial heap size of at least 1000 bytes.

-mx maxmem[k|m]

Specifies the maximum heap size the interpreter will use for dynamically allocated objects and arrays. maxmem is specified in bytes by default. You can specify maxmem in kilobytes by appending the letter k and in megabytes by appending the letter m. The default is 16 MB. You must not specify a heap size less than 1000 bytes.

-noasyncgc

Do not do garbage collection asynchronously. With this option specified, java only performs garbage collection when it runs out of memory or when the garbage collector is explicitly invoked. Without this option, java runs the garbage collector as a separate, low-priority thread.

-noclassgc

Do not garbage collect loaded classes that are no longer in use. This option is only available in JDK 1.1 and later.

-noverify

Never run the byte-code verifier.

-oss stacksize[k|m]

Sets the size of each thread's Java code stack. By default, stacksize is specified in bytes. You can specify it in kilobytes by appending the letter k or in megabytes by appending the letter m. The default value is 400 KB. You must specify at least 1000 bytes.

-prof[:file]

Output profiling information to the specified file or to the file java.prof in the current directory. The format of this profiling information is not well documented. Prior to JDK 1.1, no file can be specified; profiling information is always output to ./java.prof.

-ss stacksize[k|m]

Sets the size of each thread's native code stack. By default, stacksize is specified in bytes. You can specify it in kilobytes by appending the letter k or in megabytes by appending the letter m. The default value is 128 KB. You must specify at least 1000 bytes.

-t

Output a trace of all bytecodes executed. java_g only.

-tm

Output a trace of all methods executed. java_g only.

-v, -verbose

Print a terminal message each time java loads a class.

-verbosegc

Print a message whenever the garbage collector frees memory.

-verify

Run the byte-code verifier on all classes that are loaded.

-verifyremote

Run the byte-code verifier on all classes that are loaded through a class loader. (This generally means classes that are dynamically loaded from an untrusted location.) This is the default behavior for java.

-version

Print the version of the Java interpreter and exit.

Environment

CLASSPATH

Specifies an ordered list (colon-separated on UNIX, semicolon-separated on Windows systems) of directories and ZIP files in which java should look for class definitions. When a path is specified with this environment variable, java always implicitly appends the location of the system classes to the end of the path. If this environment variable is not specified, the default path is the current directory and the system classes. This variable is overridden by the -classpath option. See -classpath above for more information on specifying paths.