Model Part 1 - ExceptionsJ8 Home « Model Part 1 - Exceptions
In this section of the case study we look at the model part of the MVC paradigm. In these four lessons we code as much of the model as we can from the information provided within the Project Proposal. The stakeholder Stocking Goods Limited have supplied us with a Stock interface that must be implemented and from this we can also derive some exception classes. In our first lesson of the section we code up the Stock interface exceptions for our model code.
Stock Interface Exceptions Top
The exception classes we need to code to honour the contract of the Stock interface are DuplicateKeyException, RecordNotFoundException and SecurityException. So to get a clean compile on the the Stock Interface we will need to code up these exceptions first. All the exception classes are similar and allow us to throw an exception alone, with a message or chained and all of these classes extend the RuntimeException class. All the exception classes can be thrown remotely and so are serialized and use a version number so that serialisation can occur without worrying about the underlying class changing between serialization and deserialization.
We also decided in the Proposal Conclusions that a situation might arise where a user tries to stock goods that have already been stocked by another user and if this happens we will need to throw a StockingException and so we will also create and compile this class.
Creating The DuplicateKeyException Class Top
The following DuplicateKeyException class will be be thrown when we try to create a record that already exists.
Create the DuplicateKeyException class in the model package and cut and paste the following code into it.
package model;
/**
* Holds any duplicate key exceptions that may occur in the StockImpl class.
*
* @author Charlie
* @version 1.0
* @see StockImpl
*
*/
public class DuplicateKeyException extends RuntimeException {
/**
* A version number for the DuplicateKeyException class so that serialisation
* can occur without worrying about the underlying class changing
* between serialisation and deserialisation.
*
*/
private static final long serialVersionUID = 2498052502L;
/**
* Create a default DuplicateKeyException instance.
*
*/
public DuplicateKeyException() {
super();
}
/**
* Create a DuplicateKeyException instance that accepts a String.
*
* @param e The string description of the exception.
*/
public DuplicateKeyException(String e) {
super(e);
}
/**
* Create a DuplicateKeyException instance and chain an exception.
*
* @param e The exception to wrap
*/
public DuplicateKeyException(Throwable e) {
super(e);
}
}
Creating The RecordNotFoundException Class Top
The following RecordNotFoundException class will be be thrown when we try to create a record that is not found which can occur when we try to read, update, delete or lock a record.
Create the RecordNotFoundException class in the model package and cut and paste the following code into it.
package model;
/**
* Holds any record not found exceptions that may occur in the StockImpl class.
*
* @author Charlie
* @version 1.0
* @see StockImpl
*
*/
public class RecordNotFoundException extends RuntimeException {
/**
* A version number for the RecordNotFoundException class so that serialisation
* can occur without worrying about the underlying class changing
* between serialisation and deserialisation.
*
*/
private static final long serialVersionUID = 2498052502L;
/**
* Create a default DuplicateKeyException instance.
*
*/
public RecordNotFoundException() {
super();
}
/**
* Create a RecordNotFoundException instance that accepts a String.
*
* @param e The string description of the exception.
*/
public RecordNotFoundException(String e) {
super(e);
}
/**
* Create a RecordNotFoundException instance and chain an exception.
*
* @param e The exception to wrap
*/
public RecordNotFoundException(Throwable e) {
super(e);
}
}
Creating The SecurityException Class Top
The following SecurityException class will be be thrown when we have a lock record mismatch which can occur when we try to update, delete or unlock a record.
Create the SecurityException class in the model package and cut and paste the following code into it.
package model;
/**
* Holds any security exceptions that may occur in the StockImpl class.
*
* @author Charlie
* @version 1.0
* @see StockImpl
*
*/
public class SecurityException extends RuntimeException {
/**
* A version number for the SecurityException class so that serialisation
* can occur without worrying about the underlying class changing
* between serialisation and deserialisation.
*
*/
private static final long serialVersionUID = 2498052502L;
/**
* Create a default SecurityException instance.
*
*/
public SecurityException() {
super();
}
/**
* Create a SecurityException instance that accepts a String.
*
* @param e The string description of the exception.
*/
public SecurityException(String e) {
super(e);
}
/**
* Create a SecurityException instance and chain an exception.
*
* @param e The exception to wrap
*/
public SecurityException(Throwable e) {
super(e);
}
}
Creating The StockingException Class Top
The following StockingException class will be be thrown when a user tries to stock goods that have already been stocked by another user.
Create the StockingException class in the model package and cut and paste the following code into it.
package model;
/**
* Holds any stocking exceptions that may occur in the StockImpl class.
*
* @author Charlie
* @version 1.0
* @see StockImpl
*
*/
public class StockingException extends Exception {
/**
* A version number for the StockingException class so that serialisation
* can occur without worrying about the underlying class changing
* between serialisation and deserialisation.
*
*/
private static final long serialVersionUID = 2498052502L;
/**
* Create a default StockingException instance.
*
*/
public StockingException() {
super();
}
/**
* Create a StockingException instance that accepts a String.
*
* @param e The string description of the exception.
*/
public StockingException(String e) {
super(e);
}
/**
* Create a StockingException instance and chain an exception.
*
* @param e The exception to wrap
*/
public StockingException(Throwable e) {
super(e);
}
}
After adding the exception classes your project structure should look similar to that in the screenshot below. Don't worry about the javadoc errors as it will disappear when we create the Stock Interface implementation class StockImpl in a later lesson.
Lesson 3 Complete
In this lesson we coded the exception classes for the Stock Interface.
Related Java Tutorials
Objects & Classes - Class Structure and Syntax
Objects & Classes - Methods
Objects & Classes - Constructors
Objects & Classes - Static Members
OO Concepts - Inheritance Concepts - Using the super keyword
Exceptions - Declaring Exceptions
Exceptions - Creating Our Own Exceptions
API Contents - Inheritance - Using the package keyword
What's Next?
In the next lesson we create the Stock Interface.