Package and Exception Handling Flashcards
What is the purpose of package in Java?
A package is used to encapsulate a group of classes, interfaces and
sub-packages. Often, it is a hierarchical structure of storing information. It is easier to organize the related classes and subpackages in this manner.
A Package also provides access protection for classes and interfaces. A package also helps in removing naming collision.
What is java.lang package?
In Java, java.lang package contains the classes that are fundamental to the design of Java programming language. The most important class in this package is Object class.
It also contains wrapper classes like- Integer, Boolean, Character etc. It provides Math class for mathematical operations
What is a static import in Java?
Static import is similar to normal import declaration. Normal import allows us to import classes from packages without using package qualifier. Static import allows us to import static members from a class without using class qualifier.
What is Exception Handling in Java?
Java provides Exception Handling mechanism to handle Runtime errors that occur in JVM. There are checked exceptions in a program that we expect to occur in certain situations.
Exception handling mechanism catches these checked exceptions and takes relevant actions.
In Java, what are the differences between a Checked and Unchecked?
Checked Exceptions extend Throwable class, but they do not extend RuntimeException or Error classes. UncheckedException extend
RuntimeException class.
Checked Exceptions are checked at compile time in Java. Unchecked Exceptions happen at Runtime, so they are not checked
at compile time.
IOException, SQLException etc. are examples of Checked Exceptions.
NullPointerException, ArithmeticException etc. are examples of Unchecked Exceptions.
What is the base class for Error and Exception classes in Java?
Error as well as Exception class is derived from Throwable class in Java.
Can we create a finally block without creating a catch block?
Yes. A finally block can follow a try block or catch block. So we can defined a finally block just after a try block.
In what scenarios, a finally block will not be executed?
Program exits by calling system.exit() call.
A fatal error causes JVM to crash.
What is the difference between
throw and throws in Java?
We use throws to suppress an error(lazy manner and not handling error) class Express throws Exception
We use throw to explicitly throw an exception
Java provides throw keyword to throw an exception from a method or a static block. Java provides throws keyword to mention the probable exception thrown by a method in its declaration. We use throw to explicitly throw an exception. We used
throws to declare an exception in method definition.
We cannot propagate checked exceptions with throw only. But checked exceptions can be propagated with throws keyword.
A throw call is followed by an instance. Class or Exception follows a throws keyword.
Call to throw occurs within a method. throws is just used with method signature.
We can throw only one exception at a time. But we can mention as many exceptions in throws clause.
What is the concept of Exception Propagation?
In Exception Propagation, uncaught exceptions are propagated in the call stack until stack becomes empty. This propagation is called
Exception Propagation.
Let say an exception propagates from one method to another method. A() calls B(), which calls C(), which calls D(). And if D() throws
an exception, the exception will propagate from D to C to B to A, unless one of the methods catches the exception.
When we override a method in
a Child class, can we throw an
additional Exception that is not
thrown by the Parent class method?
Yes, Java allows us to throw additional Exception in a child class,
but the additional exception should be an unchecked exception
(RuntimeException).
