CS2305-
PROGRAMMING PARADIGMS
2-MARK
Questions and Answers
UNIT
I
OBJECT-ORIENTED PROGRAMMING – FUNDAMENTALS
1) What is meant by
Object Oriented Programming?
OOP is a method of programming in which programs are
organised as cooperative collections of objects. Each object is an instance of
a class and each class belong to a hierarchy.
2) What is a Class?
Class is a template for a set of objects that share a
common structure and a common behaviour.
3) What is an Object?
Object is an instance of a class. It has state,behaviour and identity. It is
also called as an instance of a class.
4) What is an Instance?
An instance has state, behaviour and identity. The
structure and behaviour of similar classes are defined in their common class. An
instance is also called as an object.
5) What are the core
OOP’s concepts?
Abstraction, Encapsulation,Inheritance and
Polymorphism are the core OOP’s concepts.
6) What is meant by
abstraction?
Abstraction defines the essential characteristics of
an object that distinguish it from all other kinds of objects. Abstraction
provides crisply-defined conceptual boundaries relative to the perspective of
the viewer. Its the process of focussing on the essential characteristics of an
object. Abstraction is one of the fundamental elements of the object model.
7) What is meant by
Encapsulation?
Encapsulation is the process of compartmentalising the
elements of an abtraction that defines the structure and behaviour.
Encapsulation helps to separate the contractual interface of an abstraction and
implementation.
8) What are Encapsulation, Inheritance and Polymorphism? Encapsulation is the mechanism that binds together code and data it manipulates and keeps both safe from outside interference and misuse. Inheritance is the process by which one object acquires the properties of another object. Polymorphism is the feature that allows one interface to be used for general class actions.
9) What are methods and how are they defined? Methods are functions that operate on instances of classes in which they are defined. Objects can communicate with each other using methods and can call methods in other classes. Method definition has four parts. They are name of the method, type of object or primitive type the method returns, a list of parameters and the body of the method. A method’s signature is a combination of the first three parts mentioned above.
10) What are different types of access modifiers (Access specifiers)? Access specifiers are
keywords that determine the type of access to the member of a class. These
keywords are for allowing
privileges to parts of a program such as functions and variables. These are:
public: Any thing declared as public can
be accessed from anywhere. private: Any thing declared as private
can’t be seen outside of its class. protected: Any thing declared as protected
can be accessed by classes in the same package and subclasses in the other
packages. default
modifier : Can be accessed only
to classes in the same package.
11)
What is an Object and how do you
allocate memory to it? Object
is an instance of a class and it is a software unit that combines a structured
set of data with a set of operations for inspecting and manipulating that data.
When an object is created using new operator, memory is allocated to it.
12) Explain the usage of Java
packages.
This
is a way to organize files when a project consists of multiple modules. It also
helps resolve naming conflicts when different packages have classes with the
same names. Packages access level also allows you to protect data from being
used by the non-authorized classes.
13) What is method
overloading and method overriding? Method overloading: When a
method in a class having the same method name with different arguments is said
to be method overloading. Method overriding : When a method in a class having
the same method name with same arguments is said to be method overriding.
14) What gives java it’s “write once and
run anywhere” nature? All Java programs are compiled into
class files that contain bytecodes. These byte codes can be run in any platform
and hence java is said to be platform independent.
15) What is a
constructor? What is a destructor?
Constructor is an operation that creates an object
and/or initialises its state. Destructor is an operation that frees the state
of an object and/or destroys the object itself. In Java, there is no concept of
destructors. Its taken care by the JVM.
16) What is the difference between constructor and method? Constructor will be automatically invoked when an object is created whereas method has to be called explicitly
17) What is Static member classes? A static member class is a static member of a class. Like any other static method, a static member class has access to all static methods of the parent, or top-level, class.
18) What is Garbage Collection and how to call it explicitly? When an object is no longer referred to by any variable, java automatically reclaims memory used by that object. This is known as garbage collection. System. gc() method may be used to call it explicitly
19) In Java, How to make an object
completely encapsulated?
All the instance variables should be declared as
private and public getter and setter methods should be provided for accessing
the instance variables.
20) What is static variable and static method? static variable is a class variable which value remains constant for the entire class
static method is the one which can be called with the class itself and can hold only the staic variables
21) What is finalize() method? finalize () method is used just before an object is destroyed and can be called just prior to garbage collection.
22) What is the difference between String and String
Buffer?
a) String objects are constants and immutable whereas StringBuffer objects are
not. b) String class supports constant strings whereas StringBuffer class
supports growable and modifiable strings.
23) What is the difference between Array and vector? Array is a set of related data type and static whereas vector is a growable array of objects and dynamic
24)
What is a package?
A package is a collection of classes and interfaces that provides a high-level
layer of access protection and name space management.
25)
What is the difference between this()
and super()?
this() can be used to invoke a constructor of the same class whereas super()
can be used to invoke a super class constructor.
26) Explain working of Java Virtual Machine
(JVM)? JVM is an abstract
computing machine like any other real computing machine which first converts
.java file into .class file by using Compiler (.class is nothing but byte code
file.) and Interpreter reads byte codes.
UNIT
II
OBJECT-ORIENTED
PROGRAMMING – INHERITANCE
1) What is meant by
Inheritance?
Inheritance is a relationship among classes, wherein
one class shares the structure or behaviour defined in another class. This is
called Single Inheritance. If a class shares the structure or behaviour from
multiple classes, then it is called Multiple Inheritance. Inheritance defines
“is-a” hierarchy among classes in which one subclass inherits from one or more
generalised superclasses.
2) What is meant by Inheritance and what
are its advantages? Inheritance is the
process of inheriting all the features from a class. The advantages of
inheritance are reusability of code and accessibility of variables and methods
of the super class by subclasses.
3) What
is the difference between superclass and subclass? A super class is a class
that is inherited whereas sub class is a class that does the inheriting.
4) Differentiate between a Class and an Object?
The Object class is the highest-level class in the Java class
hierarchy. The Class class is used to represent the classes and interfaces that
are loaded by a Java program. The Class class is used to obtain information
about an object's design. A Class is only a definition or prototype of real
life object. Whereas an object is an instance or living representation of real
life object. Every object belongs to a class and every class contains one or
more related objects.
5) What is meant by
Binding? Binding
denotes association of a name with a class
6) What is meant by Polymorphism?
Polymorphism literally means taking more than one
form. Polymorphism is a characteristic of being able to assign a different
behavior or value in a subclass, to something that was declared in a parent
class.
7) What
is Dynamic Binding?
Binding
refers to the linking of a procedure call to the code to be executed in
response to the call. Dynamic binding (also known as late binding) means that
the code associated with a given procedure call is not known until the time of
the call at run-time. It is associated with polymorphism and inheritance.
8) What is final modifier? The final modifier keyword makes that the programmer cannot change the value anymore. The actual meaning depends on whether it is applied to a class, a variable, or a method.
9) What is an Abstract
Class?
Abstract class is a class that has no instances. An abstract class is written
with the expectation that its concrete subclasses will add to its structure and
behaviour, typically by implementing its abstract operations.
10) What are inner class and anonymous class? Inner class: classes defined in other classes, including those defined in methods are called inner classes. An inner class can have any accessibility including private. Anonymous class: Anonymous class is a class defined inside a method without a name and is instantiated and declared in the same place and cannot have explicit constructors
11) What is an Interface?
Interface is an outside view of a class or object which emphaizes its
abstraction while hiding its structure and secrets of its behaviour.
12) What is a base class?
Base class is the most generalised class in a class structure. Most
applications have such root classes. In Java, Object is the base class for all
classes.
13)
What is reflection in java? Reflection allows Java code to
discover information about the fields, methods and constructors of loaded
classes and to dynamically invoke them.
14) Define superclass and
subclass?
Superclass is a class from which
another class inherits. Subclass
is a class that inherits from one or more classes.
15) What is meant by
Binding,
Static binding, Dynamic
binding?
Binding: Binding denotes
association of a name with a class. Static binding: Static binding is a binding
in which the class association is made during compile time. This is also called
as Early binding. Dynamic
binding: Dynamic binding is a binding
in which the class association is not made until the object is created at
execution time. It is also called as Late
binding.
16) What
is reflection API? How are they implemented? Reflection is the process of
introspecting the features and state of a class at runtime and dynamically
manipulate at run time. This is supported using Reflection API with built-in
classes like Class, Method, Fields, Constructors etc. Example: Using Java
Reflection API we can get the class name, by using the getName method.
17) What is the difference between a static and a non-static inner class? A non-static inner class may have object instances that are associated with instances of the class's outer class. A static inner class does not have any object instances.
18) What is the difference between abstract
class and interface? a)
All the methods declared inside an interface are abstract whereas abstract
class must have at least one abstract method and others may be concrete or
abstract. b) In abstract class, key word
abstract must be used for the methods whereas interface we need not use that
keyword for the methods. c)
Abstract class must have subclasses whereas interface can’t have subclasses.
19) Can
you have an inner class inside a method and what variables can you access? Yes,
we can have an inner class inside a method and final variables can be accessed.
20) What is interface and its use? Interface is similar to a class which may contain method’s signature only but not bodies and it is a formal set of method and constant declarations that must be defined by the class that implements it. Interfaces are useful for: a) Declaring methods that one or more classes are expected to implement b) Capturing similarities between unrelated classes without forcing a class relationship. c) Determining an object’s programming interface without revealing the actual body of the class.
21)
How is polymorphism acheived in java?
Inheritance, Overloading and Overriding are used to
acheive Polymorphism in java.
22) What modifiers may be used with top-level class? public, abstract and final can be used for top-level class.
23) What is a cloneable interface and how many methods does it contain? It is not having any method because it is a TAGGED or MARKER interface.
24) What are the methods provided by the object class? The Object class provides five methods
that are critical when writing multithreaded Java programs:
·
notify
·
notifyAll
·
wait
(three versions)
25) Define: Dynamic proxy. A dynamic proxy is a class
that implements a list of interfaces, which you specify at runtime when you
create the proxy. To create a proxy, use the static method java.lang.reflect.Proxy::newProxyInstance().
This method takes three arguments:
- The class loader to define the proxy class
- An invocation handler to intercept and handle method calls
- A list of interfaces that the proxy instance implements
26) What is object cloning?
It is the process of duplicating an object so that two identical objects will
exist in the memory at the same time.
UNIT
III
EVENT-DRIVEN
PROGRAMMING
1) What is the relationship between the Canvas class and the Graphics class? A Canvas object provides access to a Graphics object via its paint() method.
2) How would you create a
button with rounded edges? There’s 2 ways. The first
thing is to know that a JButton’s edges are drawn by a Border. so you can
override the Button’s paintComponent(Graphics) method and draw a circle or
rounded rectangle (whatever), and turn off the border. Or you can create a
custom border that draws a circle or rounded rectangle around any component and
set the button’s border to it.
3) What is the difference between the ‘Font’ and
‘FontMetrics’ class? The Font Class is used to render ‘glyphs’ - the
characters you see on the screen. FontMetrics encapsulates information about a
specific font on a specific Graphics object. (width of the characters, ascent,
descent)
4) What is the difference between the paint() and repaint()
methods? The paint() method supports
painting via a Graphics object. The repaint() method is used to cause paint()
to be invoked by the AWT painting thread.
5) Which containers use a border Layout as their default layout? The window, Frame and Dialog classes use a border layout as their default layout.
6) What is the difference between applications
and applets? a)Application must be run
on local machine whereas applet needs no explicit installation on local
machine.
b)Application must be run explicitly within a java-compatible virtual machine
whereas applet loads and runs itself automatically in a java-enabled browser. c)Application
starts execution with its main method whereas applet starts execution with its
init method. d)Application can run
with or without graphical user interface whereas applet must run within a
graphical user interface.
7) Difference between
Swing and Awt? AWT are heavy-weight componenets.
Swings are light-weight components. Hence swing works faster than AWT.
8) What
is a layout manager and what are different types of layout managers available
in java AWT?
A layout manager is an object that is used to organize components in a
container. The different layouts are available are FlowLayout, BorderLayout,
CardLayout, GridLayout and GridBagLayout.
9) How are the elements
of different layouts organized? FlowLayout: The elements of a FlowLayout are organized in a top to bottom,
left to right fashion. BorderLayout:
The elements of a BorderLayout are organized at the borders (North, South,
East and West) and the center of a container. CardLayout:
The elements of a CardLayout are stacked, on top of the other, like a deck of
cards. GridLayout:
The elements of a GridLayout are of equal size and are laid out using the
square of a grid. GridBagLayout:
The elements of a GridBagLayout are organized according to a grid. However, the
elements are of different size and may occupy more than one row or column of
the grid. In addition, the rows and columns may have different sizes. The default
Layout Manager of Panel and Panel sub classes is FlowLayout.
10) Why would you use
SwingUtilities.invokeAndWait or SwingUtilities.invokeLater?
I want to update a Swing component but I’m not
in a callback. If I want the update to happen immediately (perhaps for a
progress bar component) then I’d use invokeAndWait. If I don’t care when the
update occurs, I’d use invokeLater.
11)
What is an event and what are the
models available for event handling? An event is an event
object that describes a state of change in a source. In other words, event
occurs when an action is generated, like pressing button, clicking mouse,
selecting a list, etc. There are two types of models for handling events and
they are: a) event-inheritance model and b) event-delegation model
12) What
is the difference between scrollbar and scrollpane? A Scrollbar is a Component, but not
a Container whereas Scrollpane is a Conatiner and handles its own events and
perform its own scrolling.
13) Why won’t the JVM
terminate when I close all the application windows? The AWT event dispatcher thread is not a daemon thread. You must
explicitly call System.exit to terminate the JVM.
14) What
is meant by controls and what are different types of controls in AWT? Controls are components that allow a user to interact with your
application and the AWT supports the following types of controls: Labels, Push
Buttons, Check Boxes, Choice Lists, Lists, Scrollbars, and Text Components.
These controls are subclasses of Component.
15)
What is the difference between a Choice and a List?
A Choice is
displayed in a compact form that requires you to pull it down to see the list
of available choices. Only one item may be selected from a Choice. A List may
be displayed in such a way that several List items are visible. A List supports
the selection of one or more List items.
16) What is the purpose of the enableEvents()
method?
The enableEvents() method is used to enable an event
for a particular object. Normally,an event is enabled when a listener is added
to an object for a particular event. The enableEvents() method is used by
objects that handle events by overriding their eventdispatch methods.
17)
What is the difference between the File and RandomAccessFile classes?
The File class encapsulates the files and directories
of the local file system. The RandomAccessFile class provides the methods
needed to directly access data contained in any part of a file.
18)
What is the lifecycle of an applet? init() method - Can be
called when an applet is first loaded start() method - Can be called each time
an applet is started. paint() method - Can be called when the applet is
minimized or maximized. stop() method - Can be used when the browser moves off
the applet’s page. destroy() method - Can be called when the browser is
finished with the applet.
19) What is the difference between a MenuItem and a CheckboxMenuItem? The CheckboxMenuItem class extends the MenuItem class to support a menu item that may be checked or unchecked.
20) What class is the top of the AWT event hierarchy?
The java.awt.AWTEvent class
is the highest-level class in the AWT event-class hierarchy.
21) What
is source and listener? source
: A source is an object that generates an event. This occurs when the
internal state of that object changes in some way.
listener : A listener is an object
that is notified when an event occurs. It has two major requirements. First, it
must have been registered with one or more sources to receive notifications
about specific types of events. Second, it must implement methods to receive
and process these notifications.
22) Explain how to render
an HTML page using only Swing. Use a JEditorPane or
JTextPane and set it with an HTMLEditorKit, then load the text into the pane.
23) How would you
detect a keypress in a JComboBox? This
is a trick. most people would say ‘add a KeyListener to the JComboBox’ - but
the right answer is ‘add a KeyListener to the JComboBox’s editor component.’
24) What an I/O filter? An I/O filter is an object that reads
from one stream and writes to another, usually altering the data in some way as
it is passed from one stream to another.
25) How can I create my own
GUI components? Custom
graphical components can be created by producing a class that inherits from
java.awt.Canvas. Your component should override the paint method, just like an
applet does, to provide the graphical features of the component.
UNIT
IV
GENERIC
PROGRAMMING
1) What is an
exception? An exception is an event, which
occurs during the execution of a program, that disrupts the normal flow of the
program's instructions.
2) What is error? An Error indicates that a
non-recoverable condition has occurred that should not be caught. Error, a
subclass of Throwable, is intended for drastic problems, such as
OutOfMemoryError, which would be reported by the JVM itself.
3) Which is superclass of Exception? "Throwable", the parent class of all exception
related classes.
4) What are the advantages of using exception handling?
Exception handling provides the following advantages over
"traditional" error management techniques:
5)
What are the types
of Exceptions in Java
There are
two types of exceptions in Java, unchecked exceptions and checked exceptions.
Checked
exceptions: A checked exception is some subclass of Exception (or
Exception itself), excluding class RuntimeException and its subclasses. Each method
must either handle all checked exceptions by supplying a catch clause or list
each unhandled checked exception as a thrown exception.
Unchecked
exceptions: All Exceptions that extend the RuntimeException class are
unchecked exceptions. Class Error and its subclasses also are unchecked.
6) Why Errors are Not Checked? A
unchecked exception classes which are the error classes (Error and its
subclasses) are exempted from compile-time checking because they can occur at
many points in the program and recovery from them is difficult or impossible. A
program declaring such exceptions would be pointlessly.
7)
How does a try statement determine which catch clause should be used to handle
an exception?
When an exception is thrown within the body of a try
statement, the catch clauses of the try statement are examined in the order in
which they appear. The first catch clause that is capable of handling the
exception is executed. The remaining catch clauses are ignored.
8)
What is the purpose of the finally clause of a try-catch-finally statement?
The finally
clause is used to provide the capability to execute code no matter whether or
not an exception is thrown or caught.
9) What is the difference between checked and Unchecked Exceptions
in Java? All
predefined exceptions in Java are either a checked exception or an unchecked
exception. Checked exceptions must be caught using try.. catch () block or we
should throw the exception using throws clause. If you dont, compilation of
program will fail.
10) What is the difference between
exception and error? The exception class defines mild error conditions that
your program encounters. Exceptions can occur when trying to open the file,
which does not exist, the network connection is disrupted, operands being
manipulated are out of prescribed ranges, the class file you are interested in
loading is missing. The error class defines serious error conditions that you
should not attempt to recover from. In most cases it is advisable to let the
program terminate when such an error is encountered.
11) What is the catch or declare rule for method declarations? If a checked exception may be thrown within the body of a method, the method must either catch the exception or declare it in its throws clause.
12) When is the finally
clause of a try-catch-finally statement executed? The finally clause of the
try-catch-finally statement is always executed unless the thread of execution
terminates or an exception occurs within the execution of the finally clause.
13)
What if there is a
break or return statement in try block followed by finally block?
If there is a return statement in
the try block, the finally block executes right after the return statement
encountered, and before the return executes.
14)
What are the
different ways to handle exceptions?
There are two ways to handle
exceptions:
15) How to create custom exceptions? By extending the Exception class or one of its
subclasses.
Example:
class MyException extends Exception { public MyException() { super(); } public MyException(String s) { super(s); } }
16) Can we have the try block without catch block?
Yes, we can have the try block without
catch block, but finally block should follow the try block.
Note: It is not valid to use a try clause without either a catch clause or a finally clause.
Note: It is not valid to use a try clause without either a catch clause or a finally clause.
17) What is the
difference between swing and applet? Swing is a light weight component
whereas Applet is a heavy weight Component. Applet does not require main method,
instead it needs init method.
18)
What is the use of assert keyword?
Assert
keyword validates certain expressions. It replaces the if block effectively and
throws an AssertionError on failure. The assert keyword should be used only for
critical arguments (means without that the method does nothing).
19) How does finally block
differ from finalize() method?
Finally
block will be executed whether or not an exception is thrown. So it is used to
free resoources. finalize() is a protected method in the Object class which is
called by the JVM just before an object is garbage collected.
20)
What is the difference between throw and throws clause?
throw is used to throw an exception manually, where as throws is used in the
case of checked exceptions, to tell the compiler that we haven't handled
the exception, so that the exception will be handled by the calling function.
21)
What are the different ways to generate and Exception?
There are two different ways to generate an Exception.
- Exceptions can be generated by the Java run-time system.
Exceptions
thrown by Java relate to fundamental errors that violate the rules of the Java
language or the constraints of the Java execution environment.
- Exceptions can be manually generated by your code.
Manually
generated exceptions are typically used to report some error condition to the
caller of a method.
22)
Where does Exception stand in the Java tree hierarchy?
- java.lang.Object
- java.lang.Throwable
- java.lang.Exception
- java.lang.Error
23) What is
StackOverflowError? The StackOverFlowError is an Error
Object thorwn by the Runtime System when it Encounters that your
application/code has ran out of the memory. It may occur in case of recursive
methods or a large amount of data is fetched from the server and stored in some
object. This error is generated by JVM.
e.g.
void swap(){
swap();
}
24) Explain the
exception hierarchy in java. The hierarchy is as follows: 
Throwable is a parent class off
all Exception classes. They are two types of Exceptions: Checked exceptions and
UncheckedExceptions. Both type of exceptions extends Exception class
Throwable is a parent class off
all Exception classes. They are two types of Exceptions: Checked exceptions and
UncheckedExceptions. Both type of exceptions extends Exception class
25) How do you get the descriptive information
about the Exception occurred during the program execution? All the exceptions inherit a method
printStackTrace() from the Throwable class. This method prints the stack trace
from where the exception occurred. It prints the most recently entered method
first and continues down, printing the name of each method as it works its way
down the call stack from the top.
UNIT
V
CONCURRENT
PROGRAMMING
1) Explain
different way of using thread? The
thread could be implemented by using runnable interface or by inheriting from
the Thread class. The former is more advantageous, 'cause when you are going
for multiple inheritance..the only interface can help.
2)
What are the different states of a thread ? The different thread states are ready, running, waiting and
dead.
3)
Why are there
separate wait and sleep
methods? The
static Thread.sleep(long) method
maintains control of thread execution but delays the next action until the
sleep time expires. The wait
method gives up control over thread execution indefinitely so that other
threads can run.
4) What is multithreading and what are the
methods for inter-thread communication and what is the class in
which these methods are defined? Multithreading is the
mechanism in which more than one thread run independent of each other within
the process. wait (), notify () and notifyAll() methods can be used for
inter-thread communication and these methods are in Object class. wait() : When
a thread executes a call to wait() method, it surrenders the object lock and
enters into a waiting state. notify() or notifyAll() : To remove a thread from
the waiting state, some other thread must make a call to notify() or
notifyAll() method on the same object.
5) What is synchronization and why is it important?
With
respect to multithreading, synchronization is the capability to control the
access of multiple threads to shared resources. Without synchronization, it is
possible for one thread to modify a shared object while another thread is in
the process of using or updating that object's value. This often leads to
significant errors.
6) How does
multithreading take place on a computer with a single CPU? The operating system's task
scheduler allocates execution time to multiple tasks. By quickly switching
between executing tasks, it creates the impression that tasks execute
sequentially.
7)
What is the difference between
process and thread? Process is a program in execution whereas
thread is a separate path of execution in a program.
8) What happens
when you invoke a thread's interrupt method while it is sleeping or
waiting? When
a task's interrupt() method is executed, the task enters the ready state. The
next time the task enters the running state, an InterruptedException is thrown.
9) How can we create a
thread?
A thread can be created by extending Thread class or by implementing Runnable interface.
Then we need to override the method public void run().
10) What are three ways
in which a thread can enter the waiting state?
A thread can enter the waiting
state by invoking its sleep() method, by blocking on I/O, by unsuccessfully
attempting to acquire an object's lock, or by invoking an object's wait()
method. It can also enter the waiting state by invoking its (deprecated)
suspend() method.
11) How can i tell what state a thread is in ? Prior
to Java 5, isAlive() was commonly used to test a threads state. If isAlive()
returned false the thread was either new or terminated but there was simply no
way to differentiate between the two.
12) What is synchronized keyword? In what situations you will Use
it? Synchronization is the act of
serializing access to critical sections of code. We will use this keyword when
we expect multiple threads to access/modify the same data. To understand
synchronization we need to look into thread execution manner.
13) What is serialization?
Serialization
is the process of writing complete state of java object into output stream,
that stream can be file or byte array or stream associated with TCP/IP socket.
14) What does the Serializable interface do? Serializable
is a tagging interface; it prescribes no methods. It serves to assign the
Serializable data type to the tagged class and to identify the class as one
which the developer
has designed for persistence. ObjectOutputStream serializes only those objects
which implement this interface.
15) When you will
synchronize a piece of your code? When you expect your code will be accessed by different
threads and these threads may change a particular data causing data corruption.
16) What
is daemon thread and which method is used to create the daemon thread? Daemon
thread is a low priority thread which runs intermittently in the back ground
doing the garbage collection operation for the java runtime system. setDaemon
method is used to create a daemon thread.
17) What is the difference between yielding and sleeping? When a task invokes its yield() method, it returns to the ready state. When a task invokes its sleep() method, it returns to the waiting state.
18) What is casting? There are two types of casting,
casting between primitive numeric types and casting between object references.
Casting between numeric types is used to convert larger values, such as double
values, to smaller values, such as byte values. Casting between object
references is used to refer to an object by a compatible class, interface, or
array type reference.
19) What classes of
exceptions may be thrown by a throw statement? A throw statement may throw any
expression that may be assigned to the Throwable type.
20) A Thread is runnable, how
does that work? The
Thread class' run
method normally invokes the run
method of the Runnable type it is
passed in its constructor. However, it is possible to override the thread's run
method with your own.
21) Can I
implement my own start() method?
The
Thread start()
method is not marked final, but should not be
overridden. This method contains the code that creates a new executable thread
and is very specialised. Your threaded application should either pass a Runnable
type to a new Thread, or extend Thread
and override the run() method.
22) Do
I need to use synchronized on setValue(int)? It
depends whether the method affects method local variables, class static or
instance variables. If only method local variables are changed, the value is
said to be confined
by the method and is not prone to threading issues.
23) What
is thread priority? Thread
Priority is an integer value that identifies the relative order in which it
should be executed with respect to others. The thread priority values ranging
from 1- 10 and the default value is 5. But if a thread have higher priority
doesn't means that it will execute first. The thread scheduling depends on the
OS.
24) What are the different ways in which a thread can enter into
waiting state? There are three ways for a thread to enter
into waiting state. By invoking its sleep() method, by blocking on I/O, by
unsuccessfully attempting to acquire an object's lock, or by invoking an
object's wait() method.
25) How would you implement a thread pool? The
ThreadPool class is a generic implementation of a thread pool, which takes the
following input Size of the pool to be constructed and name of the
class which implements Runnable (which has a visible default constructor) and
constructs a thread pool with active threads that are waiting for activation.
once the threads have finished processing they come back and wait once again in
the pool.
26) What is a thread group? A
thread group is a data structure that controls the state of collection of
thread as a whole managed by the particular runtime environment.
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