Prints this throwable and its backtrace to the
standard error stream. This method prints a stack trace for this
Throwable
object on the error output stream that is
the value of the field
System.err
. The first line of
output contains the result of the
Throwable.toString()
method for
this object. Remaining lines represent data previously recorded by
the method
Throwable.fillInStackTrace()
. The format of this
information depends on the implementation, but the following
example may be regarded as typical:
java.lang.NullPointerException
at MyClass.mash(MyClass.java:9)
at MyClass.crunch(MyClass.java:6)
at MyClass.main(MyClass.java:3)
This example was produced by running the program:
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]);
}
}
The backtrace for a throwable with an initialized, non-null cause
should generally include the backtrace for the cause. The format
of this information depends on the implementation, but the following
example may be regarded as typical:
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
Note the presence of lines containing the characters
"...".
These lines indicate that the remainder of the stack trace for this
exception matches the indicated number of frames from the bottom of the
stack trace of the exception that was caused by this exception (the
"enclosing" exception). This shorthand can greatly reduce the length
of the output in the common case where a wrapped exception is thrown
from same method as the "causative exception" is caught. The above
example was produced by running the program:
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 {
}