java - What exception to throw when pre-requisite method was not called? -

i have method getuser retrieves user database. method demands verify user exists (via userexists(string username) method.

if getuser method invoked , user not exist, want throw unchecked exception, exception appropriate here? thought illegalargumentexception, doesn't feel right, inputs may okay in cases, not others - not strictly "illegal". suggestions?

to me illegalargumentexception means argument illegal , illegal. th exception use illegalstateexception state of object check user not valid.

however may have exception specific enough create own.

public class usernamenotcheckedexception extends illegalstateexception {     public usernamenotcheckedexception(string message) {         super(message);     } } 

this may make debugging things easier.

a numberformatexception subclass of illegalargumentexception. ifyou try parse number 12qw4 give numberformatexception , there nothing can make valid argument later. i.e. has nothing state of anything.

the javadoc illegalstateexception states.

signals method has been invoked @ illegal or inappropriate time. in other words, java environment or java application not in appropriate state requested operation.