Throwable.java revision 2607
2362N/A * Copyright (c) 1994, 2006, Oracle and/or its affiliates. All rights reserved. 0N/A * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 0N/A * This code is free software; you can redistribute it and/or modify it 0N/A * under the terms of the GNU General Public License version 2 only, as 2362N/A * published by the Free Software Foundation. Oracle designates this 0N/A * particular file as subject to the "Classpath" exception as provided 2362N/A * by Oracle in the LICENSE file that accompanied this code. 0N/A * This code is distributed in the hope that it will be useful, but WITHOUT 0N/A * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 0N/A * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 0N/A * version 2 for more details (a copy is included in the LICENSE file that 0N/A * accompanied this code). 0N/A * You should have received a copy of the GNU General Public License version 0N/A * 2 along with this work; if not, write to the Free Software Foundation, 0N/A * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 2362N/A * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 2362N/A * or visit www.oracle.com if you need additional information or have any 2607N/A * The {@code Throwable} class is the superclass of all errors and 0N/A * exceptions in the Java language. Only objects that are instances of this 0N/A * class (or one of its subclasses) are thrown by the Java Virtual Machine or 2607N/A * can be thrown by the Java {@code throw} statement. Similarly, only 0N/A * this class or one of its subclasses can be the argument type in a 2081N/A * For the purposes of compile-time checking of exceptions, {@code 2081N/A * Throwable} and any subclass of {@code Throwable} that is not also a 2081N/A * subclass of either {@link RuntimeException} or {@link Error} are 2081N/A * regarded as checked exceptions. 0N/A * <p>Instances of two subclasses, {@link java.lang.Error} and 0N/A * {@link java.lang.Exception}, are conventionally used to indicate 0N/A * that exceptional situations have occurred. Typically, these instances 0N/A * are freshly created in the context of the exceptional situation so 0N/A * as to include relevant information (such as stack trace data). 0N/A * <p>A throwable contains a snapshot of the execution stack of its thread at 0N/A * the time it was created. It can also contain a message string that gives 0N/A * more information about the error. Finally, it can contain a <i>cause</i>: 0N/A * another throwable that caused this throwable to get thrown. The cause 0N/A * facility is new in release 1.4. It is also known as the <i>chained 0N/A * exception</i> facility, as the cause can, itself, have a cause, and so on, 0N/A * leading to a "chain" of exceptions, each caused by another. 0N/A * <p>One reason that a throwable may have a cause is that the class that 0N/A * throws it is built atop a lower layered abstraction, and an operation on 0N/A * the upper layer fails due to a failure in the lower layer. It would be bad 0N/A * design to let the throwable thrown by the lower layer propagate outward, as 0N/A * it is generally unrelated to the abstraction provided by the upper layer. 0N/A * Further, doing so would tie the API of the upper layer to the details of 0N/A * its implementation, assuming the lower layer's exception was a checked 0N/A * exception. Throwing a "wrapped exception" (i.e., an exception containing a 0N/A * cause) allows the upper layer to communicate the details of the failure to 0N/A * its caller without incurring either of these shortcomings. It preserves 0N/A * the flexibility to change the implementation of the upper layer without 0N/A * changing its API (in particular, the set of exceptions thrown by its 0N/A * <p>A second reason that a throwable may have a cause is that the method 0N/A * that throws it must conform to a general-purpose interface that does not 0N/A * permit the method to throw the cause directly. For example, suppose 0N/A * a persistent collection conforms to the {@link java.util.Collection 0N/A * Collection} interface, and that its persistence is implemented atop 2607N/A * {@code java.io}. Suppose the internals of the {@code add} method 0N/A * can throw an {@link java.io.IOException IOException}. The implementation 2607N/A * can communicate the details of the {@code IOException} to its caller 2607N/A * while conforming to the {@code Collection} interface by wrapping the 2607N/A * {@code IOException} in an appropriate unchecked exception. (The 0N/A * specification for the persistent collection should indicate that it is 0N/A * capable of throwing such exceptions.) 0N/A * <p>A cause can be associated with a throwable in two ways: via a 0N/A * constructor that takes the cause as an argument, or via the 0N/A * {@link #initCause(Throwable)} method. New throwable classes that 0N/A * wish to allow causes to be associated with them should provide constructors 0N/A * that take a cause and delegate (perhaps indirectly) to one of the 2607N/A * {@code Throwable} constructors that takes a cause. For example: 0N/A * } catch (LowLevelException le) { 0N/A * throw new HighLevelException(le); // Chaining-aware constructor 2607N/A * Because the {@code initCause} method is public, it allows a cause to be 0N/A * associated with any throwable, even a "legacy throwable" whose 0N/A * implementation predates the addition of the exception chaining mechanism to 2607N/A * {@code Throwable}. For example: 0N/A * } catch (LowLevelException le) { 0N/A * throw (HighLevelException) 2548N/A * new HighLevelException().initCause(le); // Legacy constructor 0N/A * <p>Prior to release 1.4, there were many throwables that had their own 0N/A * non-standard exception chaining mechanisms ( 0N/A * {@link ExceptionInInitializerError}, {@link ClassNotFoundException}, 0N/A * {@link java.lang.reflect.UndeclaredThrowableException}, 0N/A * {@link java.lang.reflect.InvocationTargetException}, 0N/A * {@link java.io.WriteAbortedException}, 0N/A * {@link java.security.PrivilegedActionException}, 0N/A * {@link java.awt.print.PrinterIOException}, 0N/A * {@link java.rmi.RemoteException} and 0N/A * {@link javax.naming.NamingException}). 0N/A * All of these throwables have been retrofitted to 0N/A * use the standard exception chaining mechanism, while continuing to 0N/A * implement their "legacy" chaining mechanisms for compatibility. 2607N/A * <p>Further, as of release 1.4, many general purpose {@code Throwable} 0N/A * classes (for example {@link Exception}, {@link RuntimeException}, 0N/A * {@link Error}) have been retrofitted with constructors that take 0N/A * a cause. This was not strictly necessary, due to the existence of the 2607N/A * {@code initCause} method, but it is more convenient and expressive to 0N/A * delegate to a constructor that takes a cause. 2607N/A * <p>By convention, class {@code Throwable} and its subclasses have two 0N/A * constructors, one that takes no arguments and one that takes a 2607N/A * {@code String} argument that can be used to produce a detail message. 0N/A * Further, those subclasses that might likely have a cause associated with 0N/A * them should have two more constructors, one that takes a 2607N/A * {@code Throwable} (the cause), and one that takes a 2607N/A * {@code String} (the detail message) and a {@code Throwable} (the 0N/A * <p>Also introduced in release 1.4 is the {@link #getStackTrace()} method, 0N/A * which allows programmatic access to the stack trace information that was 0N/A * previously available only in text form, via the various forms of the 0N/A * {@link #printStackTrace()} method. This information has been added to the 2607N/A * <i>serialized representation</i> of this class so {@code getStackTrace} 2607N/A * and {@code printStackTrace} will operate properly on a throwable that 0N/A * was obtained by deserialization. 0N/A * @author unascribed 0N/A * @author Josh Bloch (Added exception chaining and programmatic access to 0N/A * stack trace in 1.4.) 2081N/A * @jls3 11.2 Compile-Time Checking of Exceptions 0N/A /** use serialVersionUID from JDK 1.0.2 for interoperability */ 0N/A * Native code saves some indication of the stack backtrace in this slot. 0N/A * Specific details about the Throwable. For example, for 2607N/A * {@code FileNotFoundException}, this contains the name of 0N/A * the file that could not be found. 0N/A * The throwable that caused this throwable to get thrown, or null if this 0N/A * throwable was not caused by another throwable, or if the causative 0N/A * throwable is unknown. If this field is equal to this throwable itself, 0N/A * it indicates that the cause of this throwable has not yet been 0N/A * The stack trace, as returned by {@link #getStackTrace()}. 0N/A * This field is lazily initialized on first use or serialization and 0N/A * nulled out when fillInStackTrace is called. 2548N/A * The list of suppressed exceptions, as returned by 2548N/A * {@link #getSuppressedExceptions()}. 2548N/A /** Message for trying to suppress a null exception. */ 2548N/A /** Caption for labeling causative exception stack traces */ 2548N/A /** Caption for labeling suppressed exception stack traces */ 2607N/A * Constructs a new throwable with {@code null} as its detail message. 0N/A * The cause is not initialized, and may subsequently be initialized by a 0N/A * call to {@link #initCause}. 0N/A * <p>The {@link #fillInStackTrace()} method is called to initialize 0N/A * the stack trace data in the newly created throwable. 0N/A * Constructs a new throwable with the specified detail message. The 0N/A * cause is not initialized, and may subsequently be initialized by 0N/A * a call to {@link #initCause}. 0N/A * <p>The {@link #fillInStackTrace()} method is called to initialize 0N/A * the stack trace data in the newly created throwable. 0N/A * @param message the detail message. The detail message is saved for 0N/A * later retrieval by the {@link #getMessage()} method. 0N/A * Constructs a new throwable with the specified detail message and 0N/A * cause. <p>Note that the detail message associated with 2607N/A * {@code cause} is <i>not</i> automatically incorporated in 0N/A * this throwable's detail message. 0N/A * <p>The {@link #fillInStackTrace()} method is called to initialize 0N/A * the stack trace data in the newly created throwable. 0N/A * @param message the detail message (which is saved for later retrieval 0N/A * by the {@link #getMessage()} method). 0N/A * @param cause the cause (which is saved for later retrieval by the 2607N/A * {@link #getCause()} method). (A {@code null} value is 0N/A * permitted, and indicates that the cause is nonexistent or 0N/A * Constructs a new throwable with the specified cause and a detail 2607N/A * message of {@code (cause==null ? null : cause.toString())} (which 2607N/A * typically contains the class and detail message of {@code cause}). 0N/A * This constructor is useful for throwables that are little more than 0N/A * wrappers for other throwables (for example, {@link 0N/A * java.security.PrivilegedActionException}). 0N/A * <p>The {@link #fillInStackTrace()} method is called to initialize 0N/A * the stack trace data in the newly created throwable. 0N/A * @param cause the cause (which is saved for later retrieval by the 2607N/A * {@link #getCause()} method). (A {@code null} value is 0N/A * permitted, and indicates that the cause is nonexistent or 0N/A * Returns the detail message string of this throwable. 2607N/A * @return the detail message string of this {@code Throwable} instance 2607N/A * (which may be {@code null}). 0N/A * Creates a localized description of this throwable. 0N/A * Subclasses may override this method in order to produce a 0N/A * locale-specific message. For subclasses that do not override this 0N/A * method, the default implementation returns the same result as 0N/A * @return The localized description of this throwable. 2607N/A * Returns the cause of this throwable or {@code null} if the 0N/A * cause is nonexistent or unknown. (The cause is the throwable that 0N/A * caused this throwable to get thrown.) 0N/A * <p>This implementation returns the cause that was supplied via one of 2607N/A * the constructors requiring a {@code Throwable}, or that was set after 0N/A * creation with the {@link #initCause(Throwable)} method. While it is 0N/A * typically unnecessary to override this method, a subclass can override 0N/A * it to return a cause set by some other means. This is appropriate for 0N/A * a "legacy chained throwable" that predates the addition of chained 2607N/A * exceptions to {@code Throwable}. Note that it is <i>not</i> 2607N/A * necessary to override any of the {@code PrintStackTrace} methods, 2607N/A * all of which invoke the {@code getCause} method to determine the 0N/A * cause of a throwable. 2607N/A * @return the cause of this throwable or {@code null} if the 0N/A * cause is nonexistent or unknown. 0N/A * Initializes the <i>cause</i> of this throwable to the specified value. 0N/A * (The cause is the throwable that caused this throwable to get thrown.) 0N/A * <p>This method can be called at most once. It is generally called from 0N/A * within the constructor, or immediately after creating the 0N/A * throwable. If this throwable was created 0N/A * with {@link #Throwable(Throwable)} or 0N/A * {@link #Throwable(String,Throwable)}, this method cannot be called 0N/A * @param cause the cause (which is saved for later retrieval by the 2607N/A * {@link #getCause()} method). (A {@code null} value is 0N/A * permitted, and indicates that the cause is nonexistent or 2607N/A * @return a reference to this {@code Throwable} instance. 2607N/A * @throws IllegalArgumentException if {@code cause} is this 0N/A * throwable. (A throwable cannot be its own cause.) 0N/A * @throws IllegalStateException if this throwable was 0N/A * created with {@link #Throwable(Throwable)} or 0N/A * {@link #Throwable(String,Throwable)}, or this method has already 0N/A * been called on this throwable. 0N/A * Returns a short description of this throwable. 0N/A * The result is the concatenation of: 0N/A * <li> the {@linkplain Class#getName() name} of the class of this object 0N/A * <li> ": " (a colon and a space) 0N/A * <li> the result of invoking this object's {@link #getLocalizedMessage} 2607N/A * If {@code getLocalizedMessage} returns {@code null}, then just 0N/A * the class name is returned. 0N/A * @return a string representation of this throwable. 0N/A * Prints this throwable and its backtrace to the 0N/A * standard error stream. This method prints a stack trace for this 2607N/A * {@code Throwable} object on the error output stream that is 2607N/A * the value of the field {@code System.err}. The first line of 0N/A * output contains the result of the {@link #toString()} method for 0N/A * this object. Remaining lines represent data previously recorded by 0N/A * the method {@link #fillInStackTrace()}. The format of this 0N/A * information depends on the implementation, but the following 0N/A * example may be regarded as typical: 0N/A * java.lang.NullPointerException 0N/A * </pre></blockquote> 0N/A * This example was produced by running the program: 0N/A * public static void main(String[] args) { 0N/A * static void crunch(int[] a) { 0N/A * static void mash(int[] b) { 0N/A * System.out.println(b[0]); 0N/A * The backtrace for a throwable with an initialized, non-null cause 0N/A * should generally include the backtrace for the cause. The format 0N/A * of this information depends on the implementation, but the following 0N/A * example may be regarded as typical: 0N/A * HighLevelException: MidLevelException: LowLevelException 0N/A * Caused by: MidLevelException: LowLevelException 0N/A * Caused by: LowLevelException 2607N/A * Note the presence of lines containing the characters {@code "..."}. 0N/A * These lines indicate that the remainder of the stack trace for this 0N/A * exception matches the indicated number of frames from the bottom of the 0N/A * stack trace of the exception that was caused by this exception (the 0N/A * "enclosing" exception). This shorthand can greatly reduce the length 0N/A * of the output in the common case where a wrapped exception is thrown 0N/A * from same method as the "causative exception" is caught. The above 0N/A * example was produced by running the program: 0N/A * public class Junk { 0N/A * public static void main(String args[]) { 0N/A * } catch(HighLevelException e) { 0N/A * e.printStackTrace(); 0N/A * static void a() throws HighLevelException { 0N/A * } catch(MidLevelException e) { 0N/A * throw new HighLevelException(e); 0N/A * static void b() throws MidLevelException { 0N/A * static void c() throws MidLevelException { 0N/A * } catch(LowLevelException e) { 0N/A * throw new MidLevelException(e); 0N/A * static void d() throws LowLevelException { 0N/A * static void e() throws LowLevelException { 0N/A * throw new LowLevelException(); 0N/A * class HighLevelException extends Exception { 0N/A * HighLevelException(Throwable cause) { super(cause); } 0N/A * class MidLevelException extends Exception { 0N/A * MidLevelException(Throwable cause) { super(cause); } 0N/A * class LowLevelException extends Exception { 2548N/A * As of release 7, the platform supports the notion of 2548N/A * <i>suppressed exceptions</i> (in conjunction with automatic 2548N/A * resource management blocks). Any exceptions that were 2548N/A * suppressed in order to deliver an exception are printed out 2548N/A * beneath the stack trace. The format of this information 2548N/A * depends on the implementation, but the following example may be 2548N/A * Exception in thread "main" java.lang.Exception: Something happened 2548N/A * Suppressed: Resource$CloseFailException: Resource ID = 0 2548N/A * Note that the "... n more" notation is used on suppressed exceptions 2548N/A * just at it is used on causes. Unlike causes, suppressed exceptions are 2548N/A * indented beyond their "containing exceptions." 2548N/A * <p>An exception can have both a cause and one or more suppressed 2548N/A * Exception in thread "main" java.lang.Exception: Main block 2548N/A * Suppressed: Resource$CloseFailException: Resource ID = 2 2548N/A * Suppressed: Resource$CloseFailException: Resource ID = 1 2548N/A * Caused by: java.lang.Exception: I did it 2548N/A * Likewise, a suppressed exception can have a cause: 2548N/A * Exception in thread "main" java.lang.Exception: Main block 2548N/A * Suppressed: Resource2$CloseFailException: Resource ID = 1 2548N/A * Caused by: java.lang.Exception: Rats, you caught me 0N/A * Prints this throwable and its backtrace to the specified print stream. 2607N/A * @param s {@code PrintStream} to use for output 2607N/A // Guard against malicious overrides of Throwable.equals by 2607N/A // using a Set with identity equality semantics. 2548N/A // Print suppressed exceptions, if any 2548N/A * Print our stack trace as an enclosed exception for the specified 2548N/A // Compute number of frames in common between this and enclosing trace 2548N/A for (
int i =
0; i <= m; i++)
2548N/A // Print suppressed exceptions, if any 0N/A * Prints this throwable and its backtrace to the specified 2607N/A * @param s {@code PrintWriter} to use for output 2548N/A * Wrapper class for PrintStream and PrintWriter to enable a single 2548N/A * implementation of printStackTrace. 2548N/A /** Returns the object to be locked when using this StreamOrWriter */ 2548N/A /** Prints the specified string as a line on this StreamOrWriter */ 0N/A * Fills in the execution stack trace. This method records within this 2607N/A * {@code Throwable} object information about the current state of 0N/A * the stack frames for the current thread. 2607N/A * @return a reference to this {@code Throwable} instance. 0N/A * @see java.lang.Throwable#printStackTrace() 0N/A * Provides programmatic access to the stack trace information printed by 0N/A * {@link #printStackTrace()}. Returns an array of stack trace elements, 0N/A * each representing one stack frame. The zeroth element of the array 0N/A * (assuming the array's length is non-zero) represents the top of the 0N/A * stack, which is the last method invocation in the sequence. Typically, 0N/A * this is the point at which this throwable was created and thrown. 0N/A * The last element of the array (assuming the array's length is non-zero) 0N/A * represents the bottom of the stack, which is the first method invocation 0N/A * <p>Some virtual machines may, under some circumstances, omit one 0N/A * or more stack frames from the stack trace. In the extreme case, 0N/A * a virtual machine that has no stack trace information concerning 0N/A * this throwable is permitted to return a zero-length array from this 0N/A * method. Generally speaking, the array returned by this method will 0N/A * contain one element for every frame that would be printed by 0N/A * @return an array of stack trace elements representing the stack trace 0N/A * pertaining to this throwable. 0N/A // Initialize stack trace if this is the first call to this method 0N/A * Sets the stack trace elements that will be returned by 0N/A * {@link #getStackTrace()} and printed by {@link #printStackTrace()} 0N/A * and related methods. 0N/A * This method, which is designed for use by RPC frameworks and other 0N/A * advanced systems, allows the client to override the default 0N/A * stack trace that is either generated by {@link #fillInStackTrace()} 0N/A * when a throwable is constructed or deserialized when a throwable is 0N/A * read from a serialization stream. 0N/A * @param stackTrace the stack trace elements to be associated with 2607N/A * this {@code Throwable}. The specified array is copied by this 0N/A * call; changes in the specified array after the method invocation 2607N/A * returns will have no affect on this {@code Throwable}'s stack 2607N/A * @throws NullPointerException if {@code stackTrace} is 2607N/A * {@code null}, or if any of the elements of 2607N/A * {@code stackTrace} are {@code null} 0N/A * Returns the number of elements in the stack trace (or 0 if the stack 0N/A * trace is unavailable). 1271N/A * package-protection for use by SharedSecrets. 0N/A * Returns the specified element of the stack trace. 1271N/A * package-protection for use by SharedSecrets. 0N/A * @param index index of the element to return. 2607N/A * @throws IndexOutOfBoundsException if {@code index < 0 || 2607N/A * index >= getStackTraceDepth() } 2548N/A * Adds the specified exception to the list of exceptions that 2548N/A * were suppressed, typically by the automatic resource management 2548N/A * statement, in order to deliver this exception. 2607N/A * <p>Note that when one exception {@linkplain 2607N/A * #initCause(Throwable) causes} another exception, the first 2607N/A * exception is usually caught and then the second exception is 2607N/A * thrown in response. In contrast, when one exception suppresses 2607N/A * another, two exceptions are thrown in sibling code blocks, such 2607N/A * as in a {@code try} block and in its {@code finally} block, and 2607N/A * control flow can only continue with one exception so the second 2607N/A * is recorded as a suppressed exception of the first. 2548N/A * @param exception the exception to be added to the list of 2548N/A * @throws NullPointerException if {@code exception} is null 2607N/A * @throws IllegalArgumentException if {@code exception} is this 2607N/A * throwable; a throwable cannot suppress itself. 2548N/A * Returns an array containing all of the exceptions that were 2548N/A * suppressed, typically by the automatic resource management 2548N/A * statement, in order to deliver this exception. 2548N/A * @return an array containing all of the exceptions that were 2548N/A * suppressed to deliver this exception.