1jdb(1) General Commands Manual jdb(1)
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6 jdb - The Java Debugger
7 jdb helps you find and fix bugs in Java language programs.
9
11 jdb [ options ] [ class ] [ arguments ]
12 options
15 Command-line options, as specified below.
16 class
18 Name of the class to begin debugging.
19 arguments
21 Arguments passed to the main() method of class.
22
24 The Java Debugger, jdb, is a simple command-line debugger for Java
25 classes. It is a demonstration of the Java Platform Debugger Architec‐
26 ture @
27 http://java.sun.com/javase/6/docs/technotes/guides/jpda/index.html that
28 provides inspection and debugging of a local or remote Java Virtual
29 Machine.
30 Starting a jdb Session
32 There are many ways to start a jdb session. The most frequently used
33 way is to have jdb launch a new Java Virtual Machine (VM) with the main
34 class of the application to be debugged. This is done by substituting
35 the command jdb for java in the command line. For example, if your
36 application's main class is MyClass, you use the following command to
37 debug it under JDB:
38 % jdb MyClass
40 When started this way, jdb invokes a second Java VM with any specified
43 parameters, loads the specified class, and stops the VM before execut‐
44 ing that class's first instruction.
45 Another way to use jdb is by attaching it to a Java VM that is already
47 running. Syntax for Starting a VM to which jdb will attach when the VM
48 is running is as follows. This loads in-process debugging libraries and
49 specifies the kind of connection to be made.
50 -agentlib:jdwp=transport=dt_socket,server=y,suspend=n
52 For example, the following command will run the MyClass application,
55 and allow jdb to connect to it at a later time.
56 % java -agentlib:jdwp=transport=dt_socket,address=8000,server=y,suspend=n MyClass
58 You can then attach jdb to the VM with the following commmand:
61 % jdb -attach 8000
63 Note that "MyClass" is not specified in the jdb command line in this
66 case because jdb is connecting to an existing VM instead of launching a
67 new one.
68 There are many other ways to connect the debugger to a VM, and all of
70 them are supported by jdb. The Java Platform Debugger Architecture has
71 additional documentation @
72 http://java.sun.com/javase/6/docs/technotes/guides/jpda/conninv.html on
73 these connection options. For information on starting a J2SE 1.4.2 or
74 early VM for use with jdb see 1.4.2 documentation @
75 http://java.sun.com/j2se/1.4.2/docs/technotes/guides/jpda/conninv.html
76 Basic jdb Commands
78 The following is a list of the basic jdb commands. The Java debugger
79 supports other commands which you can list using jdb's help command.
80 help, or ?
82 The most important jdb command, help displays the list of recog‐
83 nized commands with a brief description.
84 run
86 After starting jdb, and setting any necessary breakpoints, you
87 can use this command to start the execution the debugged applica‐
88 tion. This command is available only when jdb launches the
89 debugged application (as opposed to attaching to an existing VM).
90 cont
92 Continues execution of the debugged application after a break‐
93 point, exception, or step.
94 print
96 Displays Java objects and primitive values. For variables or
97 fields of primitive types, the actual value is printed. For
98 objects, a short description is printed. See the dump command
99 below for getting more information about an object.
100 NOTE: To display local variables, the containing class must have
102 been compiled with the javac -g option.
103 print supports many simple Java expressions including those with
105 method invocations, for example:
106 * print MyClass.myStaticField
108 * print myObj.myInstanceField
110 * print i + j + k (i, j, k are primities and either fields or
112 local variables)
113 * print myObj.myMethod() (if myMethod returns a non-null)
115 * print new java.lang.String("Hello").length()
117 dump
119 For primitive values, this command is identical to print. For
120 objects, it prints the current value of each field defined in the
121 object. Static and instance fields are included.
122 The dump command supports the same set of expressions as the print
124 command.
125 threads
127 List the threads that are currently running. For each thread, its
128 name and current status are printed, as well as an index that can
129 be used for other commands, for example:
130 4. (java.lang.Thread)0x1 main running
133 In this example, the thread index is 4, the thread is an instance of
134 java.lang.Thread, the thread name is "main", and it is currently
135 running,
136 thread
138 Select a thread to be the current thread. Many jdb commands are
139 based on the setting of the current thread. The thread is speci‐
140 fied with the thread index described in the threads command
141 above.
142 where
144 where with no arguments dumps the stack of the current thread.
145 where all dumps the stack of all threads in the current thread
146 group. where threadindex dumps the stack of the specified thread.
147 If the current thread is suspended (either through an event such as
149 a breakpoint or through the suspend command), local variables and
150 fields can be displayed with the print and dump commands. The up and
151 down commands select which stack frame is current.
152 Breakpoints
154 Breakpoints can be set in jdb at line numbers or at the first instruc‐
155 tion of a method, for example:
156 * stop at MyClass:22 (sets a breakpoint at the first instruction for
158 line 22 of the source file containing MyClass)
159 * stop in java.lang.String.length (sets a breakpoint at the beginnig
161 of the method java.lang.String.length)
162 * stop in MyClass.<init> (<init> identifies the MyClass constructor)
164 * stop in MyClass.<clinit> (<clinit> identifies the static initial‐
166 ization code for MyClass)
167 If a method is overloaded, you must also specify its argument types so
170 that the proper method can be selected for a breakpoint. For example,
171 "MyClass.myMethod(int,java.lang.String)", or "MyClass.myMethod()".
172 The clear command removes breakpoints using a syntax as in
174 "clear MyClass:45". Using the clear or command with no argument dis‐
175 plays a list of all breakpoints currently set. The cont command contin‐
176 ues execution.
177 Stepping
179 The step commands advances execution to the next line whether it is in
180 the current stack frame or a called method. The next command advances
181 execution to the next line in the current stack frame.
182 Exceptions
184 When an exception occurs for which there isn't a catch statement any‐
185 where in the throwing thread's call stack, the VM normally prints an
186 exception trace and exits. When running under jdb, however, control
187 returns to jdb at the offending throw. You can then use jdb to diagnose
188 the cause of the exception.
189 Use the catch command to cause the debugged application to stop at
191 other thrown exceptions, for example: "catch java.io.FileNotFoundExcep‐
192 tion" or "catch mypackage.BigTroubleException. Any exception which is
193 an instance of the specifield class (or of a subclass) will stop the
194 application at the point where it is thrown.
195 The ignore command negates the effect of a previous catch command.
197 NOTE: The ignore command does not cause the debugged VM to ignore spe‐
199 cific exceptions, only the debugger.
200
202 When you use jdb in place of the Java application launcher on the com‐
203 mand line, jdb accepts many of the same options as the java command,
204 including -D, -classpath, and -X<option>.
205 The following additional options are accepted by jdb:
207 -help
209 Displays a help message.
210 -sourcepath <dir1:dir2:...>
212 Uses the given path in searching for source files in the specified
213 path. If this option is not specified, the default path of "." is
214 used.
215 -attach <address>
217 Attaches the debugger to previously running VM using the default
218 connection mechanism.
219 -listen <address>
221 Waits for a running VM to connect at the specified address using
222 standard connector.
223 -listenany
225 Waits for a running VM to connect at any available address using
226 standard connector.
227 -launch
229 Launches the debugged application immediately upon startup of jdb.
230 This option removes the need for using the run command. The debuged
231 application is launched and then stopped just before the initial
232 application class is loaded. At that point you can set any necessary
233 breakpoints and use the cont to continue execution.
234 -listconnectors
236 List the connectors available in this VM
237 -connect
239 <connector-name>:<name1>=<value1>,... Connects to target VM using
240 named connector with listed argument values.
241 -dbgtrace [flags]
243 Prints info for debugging jdb.
244 -tclient
246 Runs the application in the Java HotSpot(tm) VM (Client).
247 -tserver
249 Runs the application in the Java HotSpot(tm) VM (Server).
250 -Joption
252 Pass option to the Java virtual machine used to run jdb. (Options
253 for the application Java virtual machine are passed to the run com‐
254 mand.) For example, -J-Xms48m sets the startup memory to 48
255 megabytes.
256 Other options are supported for alternate mechanisms for connecting the
258 debugger and the VM it is to debug. The Java Platform Debugger Archi‐
259 tecture has additional documentation @
260 http://java.sun.com/javase/6/docs/technotes/guides/jpda/conninv.html on
261 these connection alternatives.
262 Options Forwarded to Debuggee Process
264 -v -verbose[:class|gc|jni]
265 Turns on verbose mode.
266 -D<name>=<value>
268 Sets a system property.
269 -classpath <directories separated by
271 ":"> Lists directories in which to look for classes.
272 -X<option>
274 Non-standard target VM option
275
277 javac, java, javah, javap, javadoc.
278 05 Aug 2006 jdb(1)