What is Marker interface? How is it used in Java?

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The marker interface is a design pattern, used with languages that provide run-time type information about objects. It provides a way to associate metadata with a class where the language does not have explicit support for such metadata. To use this pattern, a class implements a marker interface, and code that interact with instances of … Read more

Why main() in java is declared as public static void main? What if the main method is declared as private?

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Public – main method is called by JVM to run the method which is outside the scope of project therefore the access specifier has to be public to permit call from anywhere outside the application static – When the JVM makes are call to the main method there is not object existing for the class … Read more

Why there are two Date classes; one in java.util package and another in java.sql?

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A thin wrapper around a millisecond value that allows JDBC to identify this as an SQL DATE value. A milliseconds value represents the number of milliseconds that have passed since January 1, 1970 00:00:00.000 GMT. To conform with the definition of SQL DATE, the millisecond values wrapped inside a java.sql.Date instance must be ‘normalized’ by … Read more

What is the use of the finally block? Is finally block in Java guaranteed to be called? When finally block is NOT called?

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Finally is the block of code that executes always. The code in finally block will execute even if an exception is occurred. Finally block is NOT called in following conditions If the JVM exits while the try or catch code is being executed, then the finally block may not execute. This may happen due to … Read more

What is OutOfMemoryError in java? How to deal with java.lang.OutOfMemeryError error?

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This Error is thrown when the Java Virtual Machine cannot allocate an object because it is out of memory, and no more memory could be made available by the garbage collector. Note: Its an Error (extends java.lang.Error) not Exception. Two important types of OutOfMemoryError are often encountered lang.OutOfMemoryError: Java heap space The quick solution is to add … Read more