Why must only certain Exceptions be declared as thrown in method signature

Question

when declaring a methods with "IllegalAccessException" eclipse forces me to declare the method as throwing an exception

public void a()  throws IllegalAccessException {
 if(x == 1){
   throw new IllegalAccessException("TEST);
 }
}

and in method b that uses "IllegalStateException" i dont need to declare the method as throw an exception

public void b()  {
 if(x == 1){
   throw new IllegalStateException("TEST);
 }
}

what is the different between thous exception
that one forces me tho declare the method that throw an exception and the other is not

thank you

Answer 1

Because IllegalAccessException is not RuntimeException (i.e. is checked exception) and IllegalStateException is a RuntimeException (i.e. is unchecked exception).

Read this for more information: http://stackoverflow.com/questions/2190161/difference-between-java-lang-runtimeexception-and-java-lang-exception

And this explanation on Oracle (duh!) site: http://download.oracle.com/javase/tutorial/essential/exceptions/catchOrDeclare.html

The first kind of exception is the checked exception. These are exceptional conditions that a well-written application should anticipate and recover from. For example, suppose an application prompts a user for an input file name, then opens the file by passing the name to the constructor for java.io.FileReader. Normally, the user provides the name of an existing, readable file, so the construction of the FileReader object succeeds, and the execution of the application proceeds normally. But sometimes the user supplies the name of a nonexistent file, and the constructor throws java.io.FileNotFoundException. A well-written program will catch this exception and notify the user of the mistake, possibly prompting for a corrected file name. Checked exceptions are subject to the Catch or Specify Requirement. All exceptions are checked exceptions, except for those indicated by Error, RuntimeException, and their subclasses.

The second kind of exception is the error. These are exceptional conditions that are external to the application, and that the application usually cannot anticipate or recover from. For example, suppose that an application successfully opens a file for input, but is unable to read the file because of a hardware or system malfunction. The unsuccessful read will throw java.io.IOError. An application might choose to catch this exception, in order to notify the user of the problem — but it also might make sense for the program to print a stack trace and exit.

Errors are not subject to the Catch or Specify Requirement. Errors are those exceptions indicated by Error and its subclasses.

The third kind of exception is the runtime exception. These are exceptional conditions that are internal to the application, and that the application usually cannot anticipate or recover from. These usually indicate programming bugs, such as logic errors or improper use of an API. For example, consider the application described previously that passes a file name to the constructor for FileReader. If a logic error causes a null to be passed to the constructor, the constructor will throw NullPointerException. The application can catch this exception, but it probably makes more sense to eliminate the bug that caused the exception to occur.

Runtime exceptions are not subject to the Catch or Specify Requirement. Runtime exceptions are those indicated by RuntimeException and its subclasses.

Answer 2

As you can see in the Javadoc of the JDK, the IllegalStateException is a RuntimeException, which is not the case of the IllegalAccessException.

And as stated by this Javadoc:

RuntimeException is the superclass of those exceptions that can be thrown during the normal operation of the Java Virtual Machine.

A method is not required to declare in its throws clause any subclasses of RuntimeException that might be thrown during the execution of the method but not caught.

That explains the difference.

Answer 3

IllegalAccessException is a checked exception. Checked exceptions must be declared or handled as they are expected results of an operation.

IllegalStateException is an unchecked exception. Unchecked exception are generally considered programming errors and it is not expected to receive one as part of normal program execution. When a programming error does occur, these exceptions are printed to standard error by default with a stack trace so the developer can determine what the programming error was.

Answer 4

It's part of the Java design that some exceptions need 'throw' declarations and some don't. Those that don't are called 'run time exceptions' and descend from "RuntimException". IllegalAccessException is not a runtime exception, and IllegalStateException is.

The logic behind the difference is that general exceptions are intended for exceptional cases that might occur at any time, no matter what the programmer does, and should always be handled by the programmer if they want their code to be rebust. An IllegalAccessException, or an IO Excection, might be caused by a failure of hardware, or access permissions, which are outside the programmers control. The software needs to do something when they occur, and having a throws clause forces the programmer to think about what to do. IllegalStateException is a symptom of a programmer error of some kind, and so doesn't necessarily need to be handled.