exceptions

Complete

Summary

Try-catch-finally

java

try {
	// do something that might throw and exception
} catch (Exception e) { // catches any subtype
	// handle exception, runs if exception is thrown in the try block
} finally {
	// clean up, runs regardless of exception or not
}

Throw

java

void func() throws Exception {
	...
	throw new Exception(); // use new to instantiate an exception
}

Concept

Checked exceptions

extends java.lang.Exception
errors that can be anticipated and recovered from
checked by compiler
handled using try-catch and must be defined using throws keyword

Unchecked exceptions(run-time exceptions)

extends java.lang.RuntimeException
errors that cannot be recovered from, caused by programmer error
no need to specify in method declaration
eg. divide by 0, only happens when running

Application

NullPointerException, runtime error

java

A a; // reference type declared but not instantiated
a.funcA(); // => Exception java.lang.NullPointerException

Custom exception

java

class OutOfStockException extends Exception {
  public OutOfStockException() {
    super("Not enough stock"); // passes error message string to super class
  }
}