java.lang.Throwable Maven / Gradle / Ivy

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This work corresponds to the API signatures of JSR 219: Foundation Profile 1.1. In the event of a discrepency between this work and the JSR 219 specification, which is available at http://www.jcp.org/en/jsr/detail?id=219, the latter takes precedence. */ package java.lang; import java.io.*; /** * The Throwable class is the superclass of all errors and * exceptions in the Java language. Only objects that are instances of this * class (or one of its subclasses) are thrown by the Java Virtual Machine or * can be thrown by the Java throw statement. Similarly, only * this class or one of its subclasses can be the argument type in a * catch clause. * *

Instances of two subclasses, {@link java.lang.Error} and * {@link java.lang.Exception}, are conventionally used to indicate * that exceptional situations have occurred. Typically, these instances * are freshly created in the context of the exceptional situation so * as to include relevant information (such as stack trace data). * *

A throwable contains a snapshot of the execution stack of its thread at * the time it was created. It can also contain a message string that gives * more information about the error. Finally, it can contain a cause: * another throwable that caused this throwable to get thrown. The cause * facility is new in release 1.4. It is also known as the chained * exception facility, as the cause can, itself, have a cause, and so on, * leading to a "chain" of exceptions, each caused by another. * *

One reason that a throwable may have a cause is that the class that * throws it is built atop a lower layered abstraction, and an operation on * the upper layer fails due to a failure in the lower layer. It would be bad * design to let the throwable thrown by the lower layer propagate outward, as * it is generally unrelated to the abstraction provided by the upper layer. * Further, doing so would tie the API of the upper layer to the details of * its implementation, assuming the lower layer's exception was a checked * exception. Throwing a "wrapped exception" (i.e., an exception containing a * cause) allows the upper layer to communicate the details of the failure to * its caller without incurring either of these shortcomings. It preserves * the flexibility to change the implementation of the upper layer without * changing its API (in particular, the set of exceptions thrown by its * methods). * *

A second reason that a throwable may have a cause is that the method * that throws it must conform to a general-purpose interface that does not * permit the method to throw the cause directly. For example, suppose * a persistent collection conforms to the {@link java.util.Collection * Collection} interface, and that its persistence is implemented atop * java.io. Suppose the internals of the put method * can throw an {@link java.io.IOException IOException}. The implementation * can communicate the details of the IOException to its caller * while conforming to the Collection interface by wrapping the * IOException in an appropriate unchecked exception. (The * specification for the persistent collection should indicate that it is * capable of throwing such exceptions.) * *

A cause can be associated with a throwable in two ways: via a * constructor that takes the cause as an argument, or via the * {@link #initCause(Throwable)} method. New throwable classes that * wish to allow causes to be associated with them should provide constructors * that take a cause and delegate (perhaps indirectly) to one of the * Throwable constructors that takes a cause. For example: *

 *     try {
 *         lowLevelOp();
 *     } catch (LowLevelException le) {
 *         throw new HighLevelException(le);  // Chaining-aware constructor
 *     }
 * 

 *     try {
 *         lowLevelOp();
 *     } catch (LowLevelException le) {
 *         throw (HighLevelException)
 *                 new HighLevelException().initCause(le);  // Legacy constructor
 *     }
 * 

Prior to release 1.4, there were many throwables that had their own * non-standard exception chaining mechanisms ( * {@link ExceptionInInitializerError}, {@link ClassNotFoundException}, * {@link java.lang.reflect.UndeclaredThrowableException}, * {@link java.lang.reflect.InvocationTargetException}, * {@link java.io.WriteAbortedException}, * {@link java.security.PrivilegedActionException} and * {@link java.rmi.RemoteException}). * As of release 1.4, all of these throwables have been retrofitted to * use the standard exception chaining mechanism, while continuing to * implement their "legacy" chaining mechanisms for compatibility. * NOTE: java.rmi.RemoteException is found in J2ME CDC optional * packages such as J2ME RMI Optional Package. * *

Further, as of release 1.4, many general purpose Throwable * classes (for example {@link Exception}, {@link RuntimeException}, * {@link Error}) have been retrofitted with constructors that take * a cause. This was not strictly necessary, due to the existence of the * initCause method, but it is more convenient and expressive to * delegate to a constructor that takes a cause. * *

By convention, class Throwable and its subclasses have two * constructors, one that takes no arguments and one that takes a * String argument that can be used to produce a detail message. * Further, those subclasses that might likely have a cause associated with * them should have two more constructors, one that takes a * Throwable (the cause), and one that takes a * String (the detail message) and a Throwable (the * cause). * *

Also introduced in release 1.4 is the {@link #getStackTrace()} method, * which allows programmatic access to the stack trace information that was * previously available only in text form, via the various forms of the * {@link #printStackTrace()} method. This information has been added to the * serialized representation of this class so getStackTrace * and printStackTrace will operate properly on a throwable that * was obtained by deserialization. * * @author unascribed * @author Josh Bloch (Added exception chaining and programmatic access to * stack trace in 1.4.) * @version 1.51, 03/12/05 * @since JDK1.0 */ public class Throwable implements Serializable { /** use serialVersionUID from JDK 1.0.2 for interoperability */ private static final long serialVersionUID = -3042686055658047285L; /** * Specific details about the Throwable. For example, for * FileNotFoundException, this contains the name of * the file that could not be found. * * @serial */ private java.lang.String detailMessage; /** * The throwable that caused this throwable to get thrown, or null if this * throwable was not caused by another throwable, or if the causative * throwable is unknown. If this field is equal to this throwable itself, * it indicates that the cause of this throwable has not yet been * initialized. * * @serial * @since 1.4 */ private java.lang.Throwable cause; /** * The stack trace, as returned by {@link #getStackTrace()}. * * @serial * @since 1.4 */ private java.lang.StackTraceElement[] stackTrace; /** * Constructs a new throwable with null as its detail message. * The cause is not initialized, and may subsequently be initialized by a * call to {@link #initCause}. * *

The {@link #fillInStackTrace()} method is called to initialize * the stack trace data in the newly created throwable. */ public Throwable() { } /** * Constructs a new throwable with the specified detail message. The * cause is not initialized, and may subsequently be initialized by * a call to {@link #initCause}. * *

The {@link #fillInStackTrace()} method is called to initialize * the stack trace data in the newly created throwable. * * @param message the detail message. The detail message is saved for * later retrieval by the {@link #getMessage()} method. */ public Throwable(java.lang.String message) { } /** * Constructs a new throwable with the specified detail message and * cause.

Note that the detail message associated with * cause is not automatically incorporated in * this throwable's detail message. * *

The {@link #fillInStackTrace()} method is called to initialize * the stack trace data in the newly created throwable. * * @param message the detail message (which is saved for later retrieval * by the {@link #getMessage()} method). * @param cause the cause (which is saved for later retrieval by the * {@link #getCause()} method). (A null value is * permitted, and indicates that the cause is nonexistent or * unknown.) * @since 1.4 */ public Throwable(java.lang.String message, java.lang.Throwable cause) { } /** * Constructs a new throwable with the specified cause and a detail * message of (cause==null ? null : cause.toString()) (which * typically contains the class and detail message of cause). * This constructor is useful for throwables that are little more than * wrappers for other throwables (for example, {@link * java.security.PrivilegedActionException}). * *

The {@link #fillInStackTrace()} method is called to initialize * the stack trace data in the newly created throwable. * * @param cause the cause (which is saved for later retrieval by the * {@link #getCause()} method). (A null value is * permitted, and indicates that the cause is nonexistent or * unknown.) * @since 1.4 */ public Throwable(java.lang.Throwable cause) { } /** * Returns the detail message string of this throwable. * * @return the detail message string of this Throwable instance * (which may be null). */ public java.lang.String getMessage() { return null; } /** * Creates a localized description of this throwable. * Subclasses may override this method in order to produce a * locale-specific message. For subclasses that do not override this * method, the default implementation returns the same result as * getMessage(). * * @return The localized description of this throwable. * @since JDK1.1 */ public java.lang.String getLocalizedMessage() { return null; } /** * Returns the cause of this throwable or null if the * cause is nonexistent or unknown. (The cause is the throwable that * caused this throwable to get thrown.) * *

This implementation returns the cause that was supplied via one of * the constructors requiring a Throwable, or that was set after * creation with the {@link #initCause(Throwable)} method. While it is * typically unnecessary to override this method, a subclass can override * it to return a cause set by some other means. This is appropriate for * a "legacy chained throwable" that predates the addition of chained * exceptions to Throwable. Note that it is not * necessary to override any of the PrintStackTrace methods, * all of which invoke the getCause method to determine the * cause of a throwable. * * @return the cause of this throwable or null if the * cause is nonexistent or unknown. * @since 1.4 */ public java.lang.Throwable getCause() { return null; } /** * Initializes the cause of this throwable to the specified value. * (The cause is the throwable that caused this throwable to get thrown.) * *

This method can be called at most once. It is generally called from * within the constructor, or immediately after creating the * throwable. If this throwable was created * with {@link #Throwable(Throwable)} or * {@link #Throwable(String,Throwable)}, this method cannot be called * even once. * * @param cause the cause (which is saved for later retrieval by the * {@link #getCause()} method). (A null value is * permitted, and indicates that the cause is nonexistent or * unknown.) * @return a reference to this Throwable instance. * @throws IllegalArgumentException if cause is this * throwable. (A throwable cannot be its own cause.) * @throws IllegalStateException if this throwable was * created with {@link #Throwable(Throwable)} or * {@link #Throwable(String,Throwable)}, or this method has already * been called on this throwable. * @since 1.4 */ public synchronized java.lang.Throwable initCause(java.lang.Throwable cause) { return null; } /** * Returns a short description of this throwable. * If this Throwable object was created with a non-null detail * message string, then the result is the concatenation of three strings: *

*
• The name of the actual class of this object *
• ": " (a colon and a space) *
• The result of the {@link #getMessage} method for this object *

     * java.lang.NullPointerException
     *         at MyClass.mash(MyClass.java:9)
     *         at MyClass.crunch(MyClass.java:6)
     *         at MyClass.main(MyClass.java:3)
     * 

     * class MyClass {
     *     public static void main(String[] args) {
     *         crunch(null);
     *     }
     *     static void crunch(int[] a) {
     *         mash(a);
     *     }
     *     static void mash(int[] b) {
     *         System.out.println(b[0]);
     *     }
     * }
     * 

     * HighLevelException: MidLevelException: LowLevelException
     *         at Junk.a(Junk.java:13)
     *         at Junk.main(Junk.java:4)
     * Caused by: MidLevelException: LowLevelException
     *         at Junk.c(Junk.java:23)
     *         at Junk.b(Junk.java:17)
     *         at Junk.a(Junk.java:11)
     *         ... 1 more
     * Caused by: LowLevelException
     *         at Junk.e(Junk.java:30)
     *         at Junk.d(Junk.java:27)
     *         at Junk.c(Junk.java:21)
     *         ... 3 more
     * 

     * public class Junk {
     *     public static void main(String args[]) { 
     *         try {
     *             a();
     *         } catch(HighLevelException e) {
     *             e.printStackTrace();
     *         }
     *     }
     *     static void a() throws HighLevelException {
     *         try {
     *             b();
     *         } catch(MidLevelException e) {
     *             throw new HighLevelException(e);
     *         }
     *     }
     *     static void b() throws MidLevelException {
     *         c();
     *     }   
     *     static void c() throws MidLevelException {
     *         try {
     *             d();
     *         } catch(LowLevelException e) {
     *             throw new MidLevelException(e);
     *         }
     *     }
     *     static void d() throws LowLevelException { 
     *        e();
     *     }
     *     static void e() throws LowLevelException {
     *         throw new LowLevelException();
     *     }
     * }
     *
     * class HighLevelException extends Exception {
     *     HighLevelException(Throwable cause) { super(cause); }
     * }
     *
     * class MidLevelException extends Exception {
     *     MidLevelException(Throwable cause)  { super(cause); }
     * }
     * 
     * class LowLevelException extends Exception {
     * }
     *