java — the Java application launcher
The java tool launches a Java application. It does this by starting a Java runtime environment, loading a specified class, and invoking that class’s main method. This method must have the following signature:
public static void main(String[])
By default, the first non-option argument is the name of the class to be invoked. A fully-qualified class name should be used. If the -jar option is specified, the first non-option argument is the name of a JAR archive containing class and resource files for the application, with the startup class indicated by the Main-Class manifest header.
The Java runtime searches for the startup class, and other classes used, in three sets of locations: the bootstrap class path, the installed extensions, and the user class path.
Non-option arguments after the class name or JAR file name are passed to the main function.
On Win32 systems, java comes in four variations: java The basic launcher tool, which implements all 1.2 features and runs in the Win32 character subsystem. Shortcuts that use java create a console window.
javaw Like java, but runs in the Win32 GUI subsystem. Shortcuts that use javaw do not create a console window. If run from an existing console window, the command returns immediately. Output to System.out and System.err is discarded. Use of System.in is not supported.
oldjava A limited-feature launcher tool, which supports programming techniques that are incompatible with some 1.2 features.
oldjavaw Like oldjava, but runs in the Win32 GUI subsystem.
JAVA AND OLDJAVA
- The oldjava launcher does not support 1.2 security features, such as system policies. Java 1.1 platform security features are fully supported.
- The oldjava launcher does not support the extension mechanism. Extension packages can still be used as class and resource archives.
- The oldjava launcher uses the bootstrap class loader for all classes, while the java launcher uses the bootstrap class loader only for bootstrap classes. This allows programming techniques that are incompatible with the base class loader.
- With java, the -classpath and -cp options specify a search path for user classes, and cannot be used to specify locations for bootstrap classes. With oldjava the -classpath and -cp options specify locations for all classes, including botstrap classes.
Note that java and oldjava do not differ in their use of the CLASSPATH environment variable. Unless overridden by -classpath or -cp, CLASSPATH always specifies the location of user classes, but says nothing about the bootstrap classes.
THE JIT
- Set the environment variable JAVA_COMPILER to «NONE», using the NT System Control Panel applet or the set command.
- Use -D option to set java.compiler to «NONE».
OPTIONS
The launcher has a set of standard options that are supported on the current runtime environment and will be supported in future releases. An additional set of non-standard options are specific to the current virtual machine implementation and are subject to change in the future. Non-standard options begin with -X
Standard Options
-classpath classpath -cp classpath Specify a list of directories, JAR archives, and ZIP archives to search for class files. Class path entries are separated by semicolons (;). Specifying -classpath or -cp overrides any setting of the CLASSPATH environment variable.
Used with java or javaw, -classpath or -cp only specify the class path for user classes. Used with oldjava or oldjavaw, -classpath or -cp specify the class path for both user classes and bootstrap classes.
If -classpath and -cp are not used and CLASSPATH is not set, the user class path consists of the current directory ( . ).
For more information on class paths, see Configuration of JDK 1.2 Software under Win32.
-Dproperty=value Set a system property value.
-jar Execute a program encapsulated in a JAR archive. The first argument is the name of a JAR archive file instead of a startup class name. The startup class is specified by the Main-Class manifest header. The JAR file is the source of all user classes, and other user class path settings are ignored.
The oldjava and oldjavaw tools do not support the -jar option.
-verbose -verbose:class Display information about each class loaded.
-verbose:gc Report on each garbage collection event.
-verbose:jni Report information about use of native methods and other Java Native Interface activity.
-version Display version information and exit.
-? -help Display usage information and exit.
-X Display information about non-standard options and exit.
Non-Standard Options
-Xbootclasspath:bootclasspath Specify a semicolon-separated list of directories, JAR archives, and ZIP archives to search for boot class files. These are used in place of the boot class files included in the JDK 1.2 software.
-Xnoclassgc Disable class garbage collection
-Xmsn Specify the initial size of the memory allocation pool. This value must greather than 1000. To multiply the value by 1000, append the letter k. To multiply the value by 1 million, append the letter m. The default value is 1m
-Xmxn Specify the maximum size of the memory allocation pool. This value must greather than 1000. To multiply the value by 1000, append the letter k. To multiply the value by 1 million, append the letter m. The default value is 16m.
-Xprof[:file] Enable profiling. If no file is specified, write results to java.prof in the current directory.
-Xhprof[:keyword/value list> Enable heap profiling. By default, results are written to heap.prof in the current directory, the stack trace is limited to 5, the top 20 allocation sites are reported, and results are sorted by the number of allocation objects. To specify other parameters, specify one or more keyword/value pairs. Separate pairs with commas. Valid parameters are: Write report to file. depth=n Limit the stack trace to n. top=n Report the top n allocation sites. sort=x Sort order. Specify a to sort by number of allocation objects, l to sort by number of live objects.
-Xverify -Xverify:all Verify that all class files obey language constraints.
-Xverify:remote Verify only remote class files. This is the default verification level.
-Xverify:none Disable class file verification.
-Xrs Reduce the use of operating system signals.
-Xcheck:jni Perform additional check for Java Native Interface functions.