Topic : Exception Handling in java - 12 July 2014. Topic not yet complete.

Exception Handling hierarchy:

Error :  Example are OutOfMemoryError, StackOverflowError. out of scope of application.

CheckedException : Force to handle in try catch block or propagate using throws method signature.

RuntimeException : If we are throwing any runtime exception in a method, it’s not required to specify them in the method signature throws clause. due to bad programming.

Question : How to define custom runtime exception ?

Answer :

public class EmptyStackException extends RuntimeException {

 public EmptyStackException() { super(); }

 public EmptyStackException(String s) { super(s); }

 public EmptyStackException(String s, Throwable throwable) { super(s, throwable); }

 public EmptyStackException(Throwable throwable) { super(throwable); }

}

Question: How to define custom checked exception ?

Answer : public class ValidationException extends Exception { }

Question: How to convert Checked exception into Runtime Exception ?

Answer :  

Step 1 .Define your own custom Runtime exception classes.

Step 2: catch the exception in try catch block, catch the checked exception.

Step 3: throw exception in catch block, using your custom runtime exception.

Question : Throwable class ?

Answer :

public class Throwable
              extends Object
                       implements Serializable

Constructor

S.N.	Constructor & Description
1	Throwable() This constructs a new throwable with null as its detail message.
2	Throwable(String message) This constructs a new throwable with the specified detail message.
3	Throwable(String message, Throwable cause) This constructs a new throwable with the specified detail message and cause.
4	Throwable(Throwable cause) This constructs a new throwable with the specified cause and a detail message of (cause==null ? null : cause.toString()) (which typically contains the class and detail message of cause).

Class methods

S.N.	Method & Description
1	Throwable fillInStackTrace() This method fills in the execution stack trace.
2	Throwable getCause() This method returns the cause of this throwable or null if the cause is nonexistent or unknown.
3	String getLocalizedMessage() This method creates a localized description of this throwable.
4	String getMessage() This method returns the detail message string of this throwable.
5	StackTraceElement[] getStackTrace() This method provides programmatic access to the stack trace information printed by printStackTrace().
6	Throwable initCause(Throwable cause) This method initializes the cause of this throwable to the specified value.
7	void printStackTrace() This method prints this throwable and its backtrace to the standard error stream.
8	void printStackTrace(PrintStream s) This method prints this throwable and its backtrace to the specified print stream.
9	void printStackTrace(PrintWriter s) This method prints this throwable and its backtrace to the specified print writer.
10	void setStackTrace(StackTraceElement[] stackTrace) This method sets the stack trace elements that will be returned by getStackTrace() and printed by printStackTrace() and related methods.
11	String toString() This method returns a short description of this throwable.

Question : Compile time exception ??

Answer :

For example, ClassNotFoundException, IllegalAccessException, NoSuchMethodException etc..

• JVM enforces to handle or catch it: Any exception which is must to handle or catch it, while writing the program is called compile time exception.
• If your code fails to either handle a compile time exception or declare that it is thrown, your code won't compile.