Exceptions with method overriding in java

In java methods can throw the different checked/unchecked exceptions, this seems to be simple as long as we are talking about the single methods in java but when we deal with method overriding in java the concept of exception which can be thrown by overriding or overridden method are bit tricky. The overriding method cannot throw the new/broader exception than the overridden method is throwing but this case is only true for checked exception and not true for unchecked/runtime exception.

If overriding method is throwing a checked exception which is new/broader than your overridden method exception then your code will not compile.

The combination of base class overridden method and derived class overriding method with respect to exceptions can be categorized into the below five cases as:

1.    Base class method throwing no exception and derived class method is throwing exception.
       •    In case of checked exception code will not compile
       •    In case of runtimeException code will work fine.

2.    Base class method throwing less newer/broader exception than derived class method is throwing.   
       Suppose base class overridden method is throwing ArithmeticException and derived class overriding
       method is throwing general Exception so then code will not compile.
      •    In case of checked exception code will not compile
      •    In case of runtimeException code will work fine.

3.    Both base and derived class overridden method throw same exception
       •    Code will compile and run perfectly in both cases of checked and unchecked exception.

4.    Base class overridden method throwing newer/broader exception than derived class overriding method.
       Suppose base class overridden method is throwing general Exception and derived class overriding
       method is throwing ArithmeticException so then code will compile and work fine.
       •     Code will compile and run perfectly in both cases of checked and unchecked exception.

5.    Base class overridden method is throwing exception but Derived class overriding method is not 
       throwing  exception.
      •    Code will compile and run perfectly in both cases of checked and unchecked exception.

What is the difference between Checked and Unchecked Exception in Java?

Checked Exception: - All the exceptions which required to be catches and handled at the compile time otherwise a compilation error will be given are known as the checked exception. All checked exception is direct sub Class of Exception but not inherit RuntimeException.

Checked Exception are helpful in ensuring that programmer provide recovery strategy or at least handle the scenario gracefully which can fail the program execution.

Type of checked Exception:-
Following are some Examples of Checked Exception:

1.       IOException

2.       SQLException

3.       DataAccessException

4.       ClassNotFoundException

5.       InvocationTargetException

Advantages and Disadvantages of Checked Exception:-

1.       They help to execute the program by handling some known failure situations.

2.       In long programs, we can location and type of error by handling the proper exceptions.

3.       They are useful in writing the log files for a program.

4.       They make the code complex and less readable

Unchecked Exception:-

All the exceptions whose handling cannot be handled at compile time are known as the Unchecked Exceptions. They mostly arise due to programming errors like accessing method of a null object, accessing element outside an array boundary.  Unchecked Exceptions are direct sub Class of RuntimeException.

Types of Unchecked Exception:-

Here are few examples of Unchecked Exception:

1.       NullPointerException

2.       ArrayIndexOutOfBound

3.       IllegalArgumentException

4.       IllegalStateException

Some Important points:

1. Both Checked and Unchecked Exception are handled using keyword try, catch and finally.

2. In terms of Functionality Checked and Unchecked Exception are same.

3. Checked Exception handling verified during compile time.

4. Unchecked Exception are mostly programming errors

5. JDK7 provides improved Exception handling code with catching multiple Exception in one catch block and reduce amount of boiler plate code required for exception handling in Java.