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COS 9 – JAVA PROGRAMMING

MIDTERM

1st Week

Exception and Assertion

Exceptions – are a mechanism used by many programming languages to describe what to do when something unexpected happens.

Common Exceptions:

NullPointerException – this is attempt to access an attribute or method of an does not refer to an object.

FileNotFoundException – this is attempt to read from a file that does not exit.

NumberFormatException – this is attempt to parse a string into a number.

ArithmeticException – this is the result of a divided-by-zero operation for integer.

SecurityException – typically thrown in browser.

Assertion – are a way to test certain assumption about the logic of a program. It checks formula.

2 Broad Categories of Exceptions:

Checked Exceptions – are those that the programmer is expected to handle in the program, and that arise from external and conditions that can readily occur in a working programs.

Example: network failure

Unchecked exceptions – might arises from conditions that represents bugs, or situations that are considered generally too difficult for a program to handle reasonably.

a. Exception class – is the base class that represents checked and unchecked exceptions.

b. Error class – is the base class used for unchecked, serious error conditions from which your program is not expected to attempt recovery.

Error – indicates a severe problem from which recovery is difficult, if not impossible.

c. RuntimeException class – is the base class that is used for the unchecked exceptions that might arises as a result of program bugs.

- indicates a design or implementation problem.

Try-Catch Statement – can be used on smaller chunks of code.

Finally Clause – defines a block of code that always executes, regardless of whether an exception was caught.

Example:

try{

startFaucet();

waterLawn();

}catch (BrokenPipeExceptions e){

logProblem (e);

} finally {

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