JAVA PROGRAMMING
2-MARK Questions and Answers
UNIT I
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
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.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
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 aplet?
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); }
}
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
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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