Effective Java 57 Use exceptions only for exceptional conditions

Principle

1. Exceptions are, as their name implies, to be used only for exceptional conditions; they should never be used for ordinary control flow.

   // Horrible abuse of exceptions. Don't ever do this!

   try {

   int i = 0;

   while(true)

   range[i++].climb();

   } catch(ArrayIndexOutOfBoundsException e) {

   }  

2. A well-designed API must not force its clients to use exceptions for ordinary control flow.

   for (Iterator<Foo> i = collection.iterator(); i.hasNext(); ) {

   Foo foo = i.next();

   ...

   }

   If Iterator lacked the hasNext method, clients would be forced to do this instead:

   // Do not use this hideous code for iteration over a collection!

   try {

   Iterator<Foo> i = collection.iterator();

   while(true) {

   Foo foo = i.next();

   ...

   }

   } catch (NoSuchElementException e) {

   }

3. An alternative to providing a separate state-testing method is to have the state dependent method return a distinguished value such as null if it is invoked with the object in an inappropriate state. This technique would not be appropriate for Iterator, as null is a legitimate return value for the next method.
4. Guidelines to choose between a state-testing method and a distinguished return value.

Different concerns	State-testing method	Distinguished value
Concurrent Object Accessing without external synchronization/externally induced state transitions	N	Y
Performance concerns	N	Y
Other situations except the conditions above	Y	N
Readability	Y	N
Incorrect use detectable	Y	N

Summary

Exceptions are designed for use in exceptional conditions. Don't use them for ordinary control flow, and don't write APIs that force others to do so.