1 /* java.lang.Throwable -- Root class for all Exceptions and Errors
2 Copyright (C) 1998, 1999, 2002, 2004, 2005 Free Software Foundation, Inc.
4 This file is part of GNU Classpath.
6 GNU Classpath is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2, or (at your option)
11 GNU Classpath is distributed in the hope that it will be useful, but
12 WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with GNU Classpath; see the file COPYING. If not, write to the
18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
21 Linking this library statically or dynamically with other modules is
22 making a combined work based on this library. Thus, the terms and
23 conditions of the GNU General Public License cover the whole
26 As a special exception, the copyright holders of this library give you
27 permission to link this library with independent modules to produce an
28 executable, regardless of the license terms of these independent
29 modules, and to copy and distribute the resulting executable under
30 terms of your choice, provided that you also meet, for each linked
31 independent module, the terms and conditions of the license of that
32 module. An independent module is a module which is not derived from
33 or based on this library. If you modify this library, you may extend
34 this exception to your version of the library, but you are not
35 obligated to do so. If you do not wish to do so, delete this
36 exception statement from your version. */
40 import gnu
.classpath
.SystemProperties
;
42 import gnu
.java
.lang
.CPStringBuilder
;
44 import java
.io
.PrintStream
;
45 import java
.io
.PrintWriter
;
46 import java
.io
.Serializable
;
49 * Throwable is the superclass of all exceptions that can be raised.
51 * <p>There are two special cases: {@link Error} and {@link RuntimeException}:
52 * these two classes (and their subclasses) are considered unchecked
53 * exceptions, and are either frequent enough or catastrophic enough that you
54 * do not need to declare them in <code>throws</code> clauses. Everything
55 * else is a checked exception, and is ususally a subclass of
56 * {@link Exception}; these exceptions have to be handled or declared.
58 * <p>Instances of this class are usually created with knowledge of the
59 * execution context, so that you can get a stack trace of the problem spot
60 * in the code. Also, since JDK 1.4, Throwables participate in "exception
61 * chaining." This means that one exception can be caused by another, and
62 * preserve the information of the original.
64 * <p>One reason this is useful is to wrap exceptions to conform to an
65 * interface. For example, it would be bad design to require all levels
66 * of a program interface to be aware of the low-level exceptions thrown
67 * at one level of abstraction. Another example is wrapping a checked
68 * exception in an unchecked one, to communicate that failure occured
69 * while still obeying the method throws clause of a superclass.
71 * <p>A cause is assigned in one of two ways; but can only be assigned once
72 * in the lifetime of the Throwable. There are new constructors added to
73 * several classes in the exception hierarchy that directly initialize the
74 * cause, or you can use the <code>initCause</code> method. This second
75 * method is especially useful if the superclass has not been retrofitted
76 * with new constructors:<br>
82 * catch (LowLevelException lle)
84 * throw (HighLevelException) new HighLevelException().initCause(lle);
87 * Notice the cast in the above example; without it, your method would need
88 * a throws clase that declared Throwable, defeating the purpose of chainig
91 * <p>By convention, exception classes have two constructors: one with no
92 * arguments, and one that takes a String for a detail message. Further,
93 * classes which are likely to be used in an exception chain also provide
94 * a constructor that takes a Throwable, with or without a detail message
97 * <p>Another 1.4 feature is the StackTrace, a means of reflection that
98 * allows the program to inspect the context of the exception, and which is
99 * serialized, so that remote procedure calls can correctly pass exceptions.
101 * @author Brian Jones
102 * @author John Keiser
103 * @author Mark Wielaard
105 * @author Eric Blake (ebb9@email.byu.edu)
107 * @status updated to 1.4
109 public class Throwable
implements Serializable
112 * Compatible with JDK 1.0+.
114 private static final long serialVersionUID
= -3042686055658047285L;
117 * The detail message.
119 * @serial specific details about the exception, may be null
121 private final String detailMessage
;
124 * The cause of the throwable, including null for an unknown or non-chained
125 * cause. This may only be set once; so the field is set to
126 * <code>this</code> until initialized.
128 * @serial the cause, or null if unknown, or this if not yet set
131 private Throwable cause
= this;
134 * The stack trace, in a serialized form.
136 * @serial the elements of the stack trace; this is non-null, and has
140 private StackTraceElement
[] stackTrace
;
143 * Instantiate this Throwable with an empty message. The cause remains
144 * uninitialized. {@link #fillInStackTrace()} will be called to set
145 * up the stack trace.
153 * Instantiate this Throwable with the given message. The cause remains
154 * uninitialized. {@link #fillInStackTrace()} will be called to set
155 * up the stack trace.
157 * @param message the message to associate with the Throwable
159 public Throwable(String message
)
162 detailMessage
= message
;
166 * Instantiate this Throwable with the given message and cause. Note that
167 * the message is unrelated to the message of the cause.
168 * {@link #fillInStackTrace()} will be called to set up the stack trace.
170 * @param message the message to associate with the Throwable
171 * @param cause the cause, may be null
174 public Throwable(String message
, Throwable cause
)
181 * Instantiate this Throwable with the given cause. The message is then
182 * built as <code>cause == null ? null : cause.toString()</code>.
183 * {@link #fillInStackTrace()} will be called to set up the stack trace.
185 * @param cause the cause, may be null
188 public Throwable(Throwable cause
)
190 this(cause
== null ?
null : cause
.toString(), cause
);
194 * Get the message associated with this Throwable.
196 * @return the error message associated with this Throwable, may be null
198 public String
getMessage()
200 return detailMessage
;
204 * Get a localized version of this Throwable's error message.
205 * This method must be overridden in a subclass of Throwable
206 * to actually produce locale-specific methods. The Throwable
207 * implementation just returns getMessage().
209 * @return a localized version of this error message
213 public String
getLocalizedMessage()
219 * Returns the cause of this exception, or null if the cause is not known
220 * or non-existant. This cause is initialized by the new constructors,
221 * or by calling initCause.
223 * @return the cause of this Throwable
226 public Throwable
getCause()
228 return cause
== this ?
null : cause
;
232 * Initialize the cause of this Throwable. This may only be called once
233 * during the object lifetime, including implicitly by chaining
236 * @param cause the cause of this Throwable, may be null
238 * @throws IllegalArgumentException if cause is this (a Throwable can't be
240 * @throws IllegalStateException if the cause has already been set
243 public Throwable
initCause(Throwable cause
)
246 throw new IllegalArgumentException();
247 if (this.cause
!= this)
248 throw new IllegalStateException();
254 * Get a human-readable representation of this Throwable. The detail message
255 * is retrieved by getLocalizedMessage(). Then, with a null detail
256 * message, this string is simply the object's class name; otherwise
257 * the string is <code>getClass().getName() + ": " + message</code>.
259 * @return a human-readable String represting this Throwable
261 public String
toString()
263 String msg
= getLocalizedMessage();
264 return getClass().getName() + (msg
== null ?
"" : ": " + msg
);
268 * Print a stack trace to the standard error stream. This stream is the
269 * current contents of <code>System.err</code>. The first line of output
270 * is the result of {@link #toString()}, and the remaining lines represent
271 * the data created by {@link #fillInStackTrace()}. While the format is
272 * unspecified, this implementation uses the suggested format, demonstrated
273 * by this example:<br>
277 * public static void main(String args[])
283 * catch(HighLevelException e)
285 * e.printStackTrace();
288 * static void a() throws HighLevelException
294 * catch(MidLevelException e)
296 * throw new HighLevelException(e);
299 * static void b() throws MidLevelException
303 * static void c() throws MidLevelException
309 * catch(LowLevelException e)
311 * throw new MidLevelException(e);
314 * static void d() throws LowLevelException
318 * static void e() throws LowLevelException
320 * throw new LowLevelException();
323 * class HighLevelException extends Exception
325 * HighLevelException(Throwable cause) { super(cause); }
327 * class MidLevelException extends Exception
329 * MidLevelException(Throwable cause) { super(cause); }
331 * class LowLevelException extends Exception
337 * HighLevelException: MidLevelException: LowLevelException
338 * at Junk.a(Junk.java:13)
339 * at Junk.main(Junk.java:4)
340 * Caused by: MidLevelException: LowLevelException
341 * at Junk.c(Junk.java:23)
342 * at Junk.b(Junk.java:17)
343 * at Junk.a(Junk.java:11)
345 * Caused by: LowLevelException
346 * at Junk.e(Junk.java:30)
347 * at Junk.d(Junk.java:27)
348 * at Junk.c(Junk.java:21)
352 public void printStackTrace()
354 printStackTrace(System
.err
);
358 * Print a stack trace to the specified PrintStream. See
359 * {@link #printStackTrace()} for the sample format.
361 * @param s the PrintStream to write the trace to
363 public void printStackTrace(PrintStream s
)
365 s
.print(stackTraceString());
369 * Prints the exception, the detailed message and the stack trace
370 * associated with this Throwable to the given <code>PrintWriter</code>.
371 * The actual output written is implemention specific. Use the result of
372 * <code>getStackTrace()</code> when more precise information is needed.
374 * <p>This implementation first prints a line with the result of this
375 * object's <code>toString()</code> method.
377 * Then for all elements given by <code>getStackTrace</code> it prints
378 * a line containing three spaces, the string "at " and the result of calling
379 * the <code>toString()</code> method on the <code>StackTraceElement</code>
380 * object. If <code>getStackTrace()</code> returns an empty array it prints
381 * a line containing three spaces and the string
382 * "<<No stacktrace available>>".
384 * Then if <code>getCause()</code> doesn't return null it adds a line
385 * starting with "Caused by: " and the result of calling
386 * <code>toString()</code> on the cause.
388 * Then for every cause (of a cause, etc) the stacktrace is printed the
389 * same as for the top level <code>Throwable</code> except that as soon
390 * as all the remaining stack frames of the cause are the same as the
391 * the last stack frames of the throwable that the cause is wrapped in
392 * then a line starting with three spaces and the string "... X more" is
393 * printed, where X is the number of remaining stackframes.
395 * @param pw the PrintWriter to write the trace to
398 public void printStackTrace (PrintWriter pw
)
400 pw
.print(stackTraceString());
404 * We use inner class to avoid a static initializer in this basic class.
406 private static class StaticData
408 static final String nl
= SystemProperties
.getProperty("line.separator");
411 // Create whole stack trace in a stringbuffer so we don't have to print
412 // it line by line. This prevents printing multiple stack traces from
413 // different threads to get mixed up when written to the same PrintWriter.
414 private String
stackTraceString()
416 CPStringBuilder sb
= new CPStringBuilder();
419 StackTraceElement
[] stack
= getStackTrace();
420 stackTraceStringBuffer(sb
, this.toString(), stack
, 0);
423 Throwable cause
= getCause();
424 while (cause
!= null)
426 // Cause start first line
427 sb
.append("Caused by: ");
430 StackTraceElement
[] parentStack
= stack
;
431 stack
= cause
.getStackTrace();
432 if (parentStack
== null || parentStack
.length
== 0)
433 stackTraceStringBuffer(sb
, cause
.toString(), stack
, 0);
436 int equal
= 0; // Count how many of the last stack frames are equal
437 int frame
= stack
.length
-1;
438 int parentFrame
= parentStack
.length
-1;
439 while (frame
> 0 && parentFrame
> 0)
441 if (stack
[frame
].equals(parentStack
[parentFrame
]))
450 stackTraceStringBuffer(sb
, cause
.toString(), stack
, equal
);
452 cause
= cause
.getCause();
455 return sb
.toString();
458 // Adds to the given StringBuffer a line containing the name and
459 // all stacktrace elements minus the last equal ones.
460 private static void stackTraceStringBuffer(CPStringBuilder sb
, String name
,
461 StackTraceElement
[] stack
, int equal
)
463 String nl
= StaticData
.nl
;
464 // (finish) first line
469 if (stack
== null || stack
.length
== 0)
471 sb
.append(" <<No stacktrace available>>");
476 for (int i
= 0; i
< stack
.length
-equal
; i
++)
479 sb
.append(stack
[i
] == null ?
"<<Unknown>>" : stack
[i
].toString());
493 * Fill in the stack trace with the current execution stack.
495 * @return this same throwable
496 * @see #printStackTrace()
498 public Throwable
fillInStackTrace()
500 vmState
= VMThrowable
.fillInStackTrace(this);
501 stackTrace
= null; // Should be regenerated when used.
507 * Provides access to the information printed in {@link #printStackTrace()}.
508 * The array is non-null, with no null entries, although the virtual
509 * machine is allowed to skip stack frames. If the array is not 0-length,
510 * then slot 0 holds the information on the stack frame where the Throwable
511 * was created (or at least where <code>fillInStackTrace()</code> was
514 * @return an array of stack trace information, as available from the VM
517 public StackTraceElement
[] getStackTrace()
519 if (stackTrace
== null)
521 stackTrace
= new StackTraceElement
[0];
524 stackTrace
= vmState
.getStackTrace(this);
525 vmState
= null; // No longer needed
532 * Change the stack trace manually. This method is designed for remote
533 * procedure calls, which intend to alter the stack trace before or after
534 * serialization according to the context of the remote call.
536 * The contents of the given stacktrace is copied so changes to the
537 * original array do not change the stack trace elements of this
540 * @param stackTrace the new trace to use
541 * @throws NullPointerException if stackTrace is null or has null elements
544 public void setStackTrace(StackTraceElement
[] stackTrace
)
546 int i
= stackTrace
.length
;
547 StackTraceElement
[] st
= new StackTraceElement
[i
];
551 st
[i
] = stackTrace
[i
];
553 throw new NullPointerException("Element " + i
+ " null");
556 this.stackTrace
= st
;
560 * VM state when fillInStackTrace was called.
561 * Used by getStackTrace() to get an array of StackTraceElements.
562 * Cleared when no longer needed.
564 private transient VMThrowable vmState
;