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Unreachable catch block

Always contruct try-catch blocks in a way that assumes catching Exceptions from more detailed to more generic.

Example

try {
    String [] tab = null;
    System.out.println(tab[3]);
} catch (Exception e) {
    System.out.println("Exception");
} catch (NullPointerException e) {
    System.out.println("NullPointerException");
}

The above presented snippet will cause compilation error:

Unreachable catch block for NullPointerException. It is already handled by the catch block

Sun Certified Java Programmer

Okay, I’ve been working with Java for a few years now, starting from academia and ending with business solutions. So yeah, I think I can say I know Java and some of those technologies like J2SE, J2EE or J2ME, with their own standards and solutions. Therefore, I’ve decided I’d take Sun Certified Java Programmer (SCJP) in a few months.

If …

What if you extend an abstract class and implement an interface when both define a method with the same name?

Imagine you need to implement a class that extends an abstract class and implements an interface when both define a method with the same name – test().

Example

interface Implementable { public void test(); }
abstract class Superclass { public abstract void test(); }

public class Test extends Superclass implements Implementable {
    /* definition of load method(s)..... */
}

The …

Exeptions and Errors in Java

In the diagram below I present the hierarchy of most common Exceptions and Errors:

Object
 |
 |_ Throwable
    |
    |_ Error
    |   |
    |   |_ AssertionError
    |   |
    |   |_ LinkageError
    |   |   |
    |   |   |_ ExceptionInInitializerError
    |   |   |
    |   |   |_ NoClassDefFoundError
    |   |   |
    |   |_ VirtualMachineError
    |       |
    |       |_ StackOverflowError
    |
    |_ Exception
        |
        

Test your Java experience for free – JavaBlackBelt

Recently I’ve come across another very interesting social service – JavaBlackBelt. Basically it gathers programmers who use Java language and related frameworks and aspects (OO programming, JSP, Struts, JSF, EJB). There are even exams on C#, Ruby, JavaScript, and AJAX but some of them are still beta versions.

Of course I’ve taken a couple of exams and this is my …