2.1 Exceptions

Types of Exceptions

Compile Time Exception

Exceptions are checked during compile time

To be compiled successfully, the code must handle exception

• Try Catch
• Throw Exception

Otherwise, it will throw an exception during compile.

Runtime Exception

Runtime exceptions are not checked during compile.

Therefore, the developer must be able to except exceptions and be able to handle them

Most common exceptions are NullPointerException

NullPointerException happens when trying to access a null object

Throwing an Exception

see example below

throw new Exception();
throw new NullPointerException();

You can include message too.

throw new Exception("some message 1");
throw new NullPointerException("some message 2");

Handling Exceptions

Try, Catch, finally

There can be multiple catch block for try catch.

It is usual to go from specific exception to general exception. (see example below)

try{
    //code
}
catch(NullPointerException e) {
    //handle error
}
catch(Exception e) {
    //handle error
}

finally block runs even if the exception is not handled.

Thus, it can be used for cleanup process.

Postponding Exceptions

See the example below

public void someFunction() throws NullPointerException {
    // code
}

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Note for CS2114 students

You should test exception if you have exception handling code in your test.