What are checked and unchecked exceptions?
Java defines two kinds of exceptions :
Checked exceptions : Exceptions that inherit from the Exception class are checked exceptions. Client code has to handle the checked exceptions thrown by the API, either in a catch clause or by forwarding it outward with the throws clause. Examples - SQLException, IOxception
Unchecked exceptions : RuntimeException also extends from Exception.
However, all of the exceptions that inherit from RuntimeException get special
treatment. There is no requirement for the client code to deal with them,
and hence they are called unchecked exceptions. Example Unchecked exceptions
are NullPointerException, OutOfMemoryError, DivideByZeroException typically,
What is a user defined exception?
User-defined exceptions may be implemented by
* defining a class to respond to the exception and
* embedding a throw statement in the try block where the exception can occur or declaring that the method throws the exception (to another method where it is handled).
The throw statement is used to signal the occurance of the exception within a try block. Often, exceptions are instantiated in the same statement in which they are thrown using the syntax.
throw new MyException("I threw my own exception.")
To handle the exception within the method where it is thrown, a catch statement that handles MyException, must follow the try block. If the developer does not want to handle the exception in the method itself, the method must pass the exception using the syntax:
public myMethodName() throws MyException
What is the difference between C++ & Java?
Well as Bjarne Stroustrup says "..despite the syntactic similarities, C++ and Java are very different languages. In many ways, Java seems closer to Smalltalk than to C++..". Here are few I discovered:
* Java is multithreaded
* Java has no pointers
* Java has automatic memory management (garbage collection)
* Java is platform independent (Stroustrup may differ by saying "Java is a platform"
* Java has built-in support for comment documentation
* Java has no operator overloading
* Java doesn t provide multiple inheritance
* There are no destructors in Java
What are statements in JAVA ?
*declaration statement-Varible declaration. *control flow statements-For
and if statment.
What is JAR file?
JavaARchive files are a big glob of Java classes, images, audio, etc.,
compressed to make one simple, smaller file to ease Applet downloading.
Normally when a browser encounters an applet, it goes and downloads all
the files, images, audio, used by the Applet separately. This can lead
to slower downloads.
What is JNI?
JNI is an acronym of Java Native Interface. Using JNI we can call functions which are written in other languages from Java. Following are its advantages and disadvantages.
* You want to use your existing library which was previously written in other language.
* You want to call Windows API function.
* For the sake of execution speed.
* You want to call API function of some server product which is in c or c++ from java client.
* You can t say write once run anywhere.
* Difficult to debug runtime error in native code.
* Potential security risk.
* You can t call it from Applet.
Why there are some null interface in java ? What does it mean ? Give me some null interfaces in JAVA?
Null interfaces act as markers..they just tell the compiler that the
objects of this class need to be treated differently..some marker interfaces
are : Serializable, Remote, Cloneable
Is synchronised a modifier, indentifier? What is it?
It's a modifier. Synchronized methods are methods that are used to control access to an object. A thread only executes a synchronized method after it has acquired the lock for the method's object or class. Synchronized statements are similar to synchronized methods. A synchronized statement can only be executed after a thread has acquired the lock for the object or class referenced in the synchronized statement.
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