Transcript AP06-Exceptions.ppt: uploaded 1 April 2016 at 4:01 pm

Exceptions
common exceptions
throwing standard
unchecked exceptions
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A Story…
You plan a trip to HersheyPark, with the
primary purpose of riding the roller
coasters. Just after you pay for
admission and pull out the map to look
for the first roller coaster, the sky turns
dark, and you see lightning and hear
thunder. An announcement on the loudspeaker says that the park is closing.
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A Story…CCJ AP CS Study Guide (Chapter 12)
An exceptional situation causes abrupt
termination of the normal processing (the
park visit). Note that throwing an
exception doesn't tell you how to recover
from the exceptional situation. An
example of recovery would be if the
management issued rain-checks. In Java,
a catch clause is responsible for
recovering from an exceptional condition.
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An exception is:
an "exceptional event"
an event that occurs during program
execution that disrupts normal flow
not necessarily "an error."
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Some exceptions/errors
division by zero
accessing out-of-bounds array element
attempting to open non-existent file
attempting to read beyond eof marker
invalid class casting
specifying negative array sizes
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Java Exception Hierarchy
Throwable
Error
Linkage Error
Exception
(unchecked)
Runtime Exception
(checked)
IOException
ArrayOutOfBoundsException
ClassCastException
NullPointerException
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NumberFormatException
InterruptedException
FileNotFoundException
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Java Exception Hierarchy
Checked exceptions are compiler-enforced
exceptions. This means that when you call
a method that throws a checked
exception, you must tell the compiler what
you are going to do about the exception if
it is thrown. Checked exceptions are due
to external circumstances that the
programmer cannot prevent.
(NOT part of AP Subset)
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AP CS A Subset
common exceptions
throwing standard UNCHECKED exceptions

unchecked exceptions can be ignored by the
programmer; no need to use try/catch to handle
the exception
not tested:

try/catch
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Java Exception Hierarchy
Throwable
Error
Linkage Error
Exception
(unchecked)
Runtime Exception
(checked)
IOException
ArrayOutOfBoundsException
ClassCastException
NullPointerException
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NumberFormatException
InterruptedException
FileNotFOundException
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AP CS A Subset
Students are expected to understand




NullPointerException
ArrayIndexOutOfBoundsException
ArithmeticException
ClassCastException
Students are expected to be able to throw

IllegalStateException
 signals that a method has been invoked at an illegal or
inappropriate time.

NoSuchElementException
 if no more elements exist (useful with iterators)
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A look ahead…
public void add(Locatable obj){
Location loc = obj.location();
if (!isEmpty(loc)){
throw new IllegalArgumentException("Location “
+ loc + " is not a valid empty location");
}
//Add object to the environment.
theGrid[loc.row()][loc.col()]= obj;
objectCount++;
}
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