CORE JAVA Interview Questions Part3

7. Question: How to define an Abstract class?

Answer: A class containing abstract method is called Abstract class. An Abstract class can't be instantiated.

Example of Abstract class:

abstract class testAbstractClass {

protected String myString;

public String getMyString() {

return myString; }

public abstract string anyAbstractFunction();

}



8. Question: How to define an Interface?

Answer: In Java Interface defines the methods but does not implement them. Interface can include constants. A class that implements the interfaces is bound to implement all the methods defined in Interface.

Emaple of Interface:



public interface sampleInterface {

public void functionOne();

public long CONSTANT_ONE = 1000; }



9. Question: Explain the user defined Exceptions?

Answer: User defined Exceptions are the separate Exception classes defined by the user for specific purposed. An user defined can created by simply sub-classing it to the Exception class. This allows custom exceptions to be generated (using throw) and caught in the same way as normal exceptions.

Example:

class myCustomException extends Exception {

// The class simply has to exist to be an exception }



10. Question: Explain the new Features of JDBC 2.0 Core API?

Answer: The JDBC 2.0 API includes the complete JDBC API, which includes both core and Optional Package API, and provides inductrial-strength database computing capabilities.

New Features in JDBC 2.0 Core API:

• Scrollable result sets- using new methods in the ResultSet interface allows programmatically move the to particular row or to a position relative to its current position

• JDBC 2.0 Core API provides the Batch Updates functionality to the java applications.

• Java applications can now use the ResultSet.updateXXX methods.

• New data types - interfaces mapping the SQL3 data types

• Custom mapping of user-defined types (UTDs)

• Miscellaneous features, including performance hints, the use of character streams, full precision for java.math.BigDecimal values, additional security, and support for time zones in date, time, and timestamp values.

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