Section 7.2. Checked/Unchecked Exceptions and Errors

7.2. Checked/Unchecked Exceptions and Errors

Exceptions and errors fall into three categories: checked exceptions, unchecked exceptions, and errors.

7.2.1. Checked Exceptions

• Checked exceptions are checked by the compiler at compile time.

• Methods that throw a checked exception must indicate so in the method declaration using the throws clause. This must continue all the way up the calling stack until the exception is handled.

• All checked exceptions must be explicitly caught with a catch block.

• Checked exceptions include exceptions of the type Exception, and all classes that are subtypes of Exception, except for RuntimeException and the subtypes of RuntimeException.

The following is an example of a method that throws a checked exception:

	// Method declaration that throws
	// an IOException
	void readFile(String filename)
	  throws IOException {
	  ...
	}

7.2.2. Unchecked Exceptions

• The compiler does not check unchecked exceptions at compile time.

• Unchecked exceptions occur during runtime due to programmer error (out-of-bounds index, divide by zero, and null pointer exception) or system resource exhaustion.

• Unchecked exceptions do not have to be caught.

• Methods that may throw an unchecked exception do not have to (but can) indicate this in the method declaration.

• Unchecked exceptions include exceptions of the type RuntimeException and all subtypes of RuntimeException.

7.2.3. Errors

• Errors are typically unrecoverable and present serious conditions.

• Errors are not checked at compile time and do not have to be (but can be) caught/handled.

Any checked exceptions, unchecked exceptions, or errors can be caught.