JAVA LAB VIVA Questions with Answers :-
1. What is Java?
Java is a high-level programming language originally developed by Sun Microsystems and released in 1995. Java runs on a variety of platforms, such as Windows, Mac OS, and the various versions of UNIX.
2. What is the most important feature of Java?
Java is a platform independent language.
3. What do you mean by platform independence?
Platform independence means that we can write and compile the java code in one platform (eg Windows) and can execute the class in any other supported platform eg (Linux,Solaris,etc).
4. What are the supported platforms by Java Programming Language?
Java runs on a variety of platforms, such as Windows, Mac OS, and the various versions of UNIX/Linux like HP-Unix, Sun Solaris, Redhat Linux, Ubuntu, CentOS, etc.
5. What is the difference between a JDK and a JVM?
JDK is Java Development Kit which is for development purpose and it includes execution environment also. But JVM is purely a run time environment and hence you will not be able to compile your source files using a JVM.
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6. What are the access modifiers in Java?
There are 3 access modifiers. Public, protected and private, and the default one if no identifier is specified is called friendly, but programmer cannot specify the friendly identifier explicitly.
7. What is are packages?
A package is a collection of related classes and interfaces providing access protection and namespace management.
8. 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 sub classes.
9. 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.
10. What is an abstract class?
An abstract class is a class designed with implementation gaps for sub classes to fill in and is deliberately incomplete.
11. What are the states associated in the thread?
Thread contains ready, running, waiting and dead states.
12. What is synchronization?
Synchronization is the mechanism that ensures that only one thread is accessed the resources at a time.
13. What is deadlock?
When two threads are waiting each other and can’t precede the program is said to be deadlock.
14. What is an applet?
Applet is a dynamic and interactive program that runs inside a web page displayed by a java capable browser
15. 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.
16. How do you set security in applets?
using setSecurity Manager() method
17. 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
18. What is JDBC?
JDBC is a set of Java API for executing SQL statements. This API consists of a set of classes and interfaces to enable programs to write pure Java Database applications.
19. What are drivers available?
a) JDBC-ODBC Bridge driver b) Native API Partly-Java driver
c) JDBC-Net Pure Java driver d) Native-Protocol Pure Java driver
20. What is stored procedure?
Stored procedure is a group of SQL statements that forms a logical unit and performs a particular task. Stored Procedures are used to encapsulate a set of operations or queries to execute on database. Stored procedures can be compiled and executed with different parameters and results and may have any combination of input/output parameters.
21. What is the Java API?
The Java API is a large collection of ready-made software components that provide many useful capabilities, such as graphical user interface (GUI) widgets.
22. Why there are no global variables in Java?
Global variables are globally accessible. Java does not support globally accessible variables due to following reasons:
- The global variables breaks the referential transparency
- Global variables creates collisions in namespace.
23. 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.
24. What is the use of bin and lib in JDK?
Bin contains all tools such as javac, appletviewer, awt tool, etc., whereas lib contains API and all packages.
25. 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.
26. 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.
27. What is Domain Naming Service(DNS)?
It is very difficult to remember a set of numbers(IP address) to connect to the Internet. The Domain Naming Service(DNS) is used to overcome this problem. It maps one particular IP address to a string of characters. For example, www. mascom. com implies com is the domain name reserved for US commercial sites, moscom is the name of the company and www is the name of the specific computer, which is mascom’s server.
28. What is URL?
URL stands for Uniform Resource Locator and it points to resource files on the Internet. URL has four components: http://www. address. com:80/index.html, where http – protocol name, address – IP address or host name, 80 – port number and index.html – file path.
29. What is RMI and steps involved in developing an RMI object?
Remote Method Invocation (RMI) allows java object that executes on one machine and to invoke the method of a Java object to execute on another machine. The steps involved in developing an RMI object are:
- Define the interfaces
- Implementing these interfaces
- Compile the interfaces and their implementations with the java compiler
- Compile the server implementation with RMI compiler
- Run the RMI registry
- Run the application.
30. What is RMI architecture?
RMI architecture consists of four layers and each layer performs specific functions: a) Application layer – contains the actual object definition. b) Proxy layer – consists of stub and skeleton. c) Remote Reference layer – gets the stream of bytes from the transport layer and sends it to the proxy layer. d) Transportation layer – responsible for handling the actual machine-to-machine communication.
31. Why Java?
The programs that we are writing are very similar to their counterparts in several other languages, so our choice of language is not crucial. We use Java because it is widely available, embraces a full set of modern abstractions, and has a variety of automatic checks for mistakes in programs, so it is suitable for learning to program. There is no
perfect language, and you certainly will be programming in other languages in the future.
32. Do I really have to type in the programs in the book to try them out?
Everyone should type in HelloWorld.java, but you can find all of the code in this book (and much more) on this booksite.
33. What are Java’s rules regarding tabs, spaces and newline characters?
There are not many. Java compilers treat them all to be equivalent. For example, we could also write HelloWorld as follows:
public class HelloWorld { public static void main (
String [] args) { System.out.println(“Hello World”) ; } }
But we do normally adhere to spacing and indenting conventions when we write Java programs, just as we always indent paragraphs and lines consistently when we write prose or poetry.
34. What are the rules regarding quotation marks?
Material inside quotation marks is an exception to the rule of the previous question:
things within quotes are taken literally so that you can precisely specify what gets printed. If you put any number of successive spaces within the quotes, you get that number of spaces in the output. If you accidentally omit a quotation mark, the compiler may get very confused, because it needs that mark to distinguish between characters in the string and other parts of the program. To print a quotation mark, a newline, or a tab, use \”, \n, or \t, respectively, within the quotation marks.
35. What is the meaning of the words public, static and void?
These keywords specify certain properties of main() that you will learn about later in the book. For the moment, we just include these keywords in the code (because they are required) but do not refer to them in the text.
36. What happens when you omit a brace or misspell one of the words, like public or
static or main?
It depends upon precisely what you do. Such errors are called syntax errors. Try it out and see.
37. Can a program use more than one command-line argument?
Yes, you can put several, though we normally use only a few. You refer to the second one as args[1], the third one as args[2], and so forth. Note that we start counting from 0 in Java.
38. What Java systems libraries and methods are available for me to use?
There are thousands of them, but we introduce them to you in a deliberate fashion in this book to avoid overwhelming you with choices.
39. How should I format my code? How should I comment my code?
Programmers use coding guidelines to make programs easier to read, understand, and maintain. As you gain experience, you will develop a coding style, just as you develop style when writing prose. Appendix B provides some guidelines for formatting and commenting your code. We recommend returning to this appendix after you’ve written a few programs.
40. What exactly is a .class file?
It’s a binary file (sequence of 0s and 1s). If you are using Unix or OS X, you can examine its contents by typing od -x HelloWorld.class at the command prompt. This displays the results in hexadecimal (base 16). In deference to Java’s name, the first word of every .class file is cafe.
41. How do I get the | symbol on my keyboard?
It’s there. Often it’s above the \ symbol.
42. Java prints out a ton of digits when I System.out.println() a double. How can I format it so it displays only 3 digits after the decimal place?
Use the method System.out.printf() described in Section 1.5.
43. Why does the integer quotient -0/3 yield 0, but the double quotient -0.0/3.0 yields – 0.0?
Java represent integers using something called two’s complement notation, and there is only one representation of 0. (You’ll learn about this in Section 5.1.) Java represents doubles using IEEE specifications, and there are two distinct representations of the number zero, 0 and -0. (You’ll learn about this in Section 9.1.)
44. What happens when I use / and % with a negative numerator?
Try it and see. -47 / 5 = -9 and -47 % 5 = -2. The quotient is always rounded toward zero. To ensure the Euclidean property b * (a / b) + (a % b) = a, the result of the remainder operator can be negative. This convention was inherited from ancestral
languages like FORTRAN and C. Some languages (but not Java) include both remainder and modulo operators because it is often convenient to have a version that returns only nonnegative integers.
45. Can I use % with real numbers?
Yes. If angle is nonnegative, then angle % (2 * Math.PI) converts the angle to be
between 0 and 2 π.
46. How do I print a “?
Since ” is a special character when dealing with strings, you must escape the convention rules by using \”. For example, System.out.println(“The pig said \”Oink Oink\” afterwards”);.
47. OK, so then how do I print a \?
Use “\\”.
48. Why do I need to declare the type of a variable in Java?
By specifying the type, the compiler can alert you of potential errors, say if you try to multiply an integer with a string. For the same reason, when doing physics calculations, it is always a good idea to keep track of the units and make sure they “type check.” For small programs, this may not seem important; for large programs it is crucial. The Ariane 5 rocket exploded 40 seconds after takeoff because of a bug in its software that incorrectly converted a 64 bit real number into a 16 bit integer.
49. Why is the type for real numbers called double?
Historically, the type for floating point numbers was float, but they had limited
accuracy. The type double was introduced as a floating point type with twice as much
accuracy.
50. Is it correct to say that using parentheses can only change
Almost, with one surprising exception. The literal value 2147483648 (2^31) is only permitted as an operand of the unary minus operator, i.e., -2147483648. Enclosing it in parentheses, i.e., -(2147483648), leads to a compile-time error.
51.What is JVM?
The Java interpreter along with the run time environment required to run the Java application in called as Java virtual machine(JVM)
52. What is the base class of all classes?
java.lang.Object
53. Explain Set Interface?
It is a collection of element which cannot contain duplicate elements. The Set interface contains only methods inherited from Collection and adds the restriction that duplicate elements are prohibited.
54. Explain TreeSet?
It is a Set implemented when we want elements in a sorted order.
55. What is Comparable Interface?
It is used to sort collections and arrays of objects using the collections.sort() and java.utils. The objects of the class implementing the Comparable interface can be ordered.
56. Difference between throw and throws?
It includes: Throw is used to trigger an exception where as throws is used in declaration of exception. Without throws, Checked exception cannot be handled where as checked exception can be propagated with throws.
57. Explain the following line used under Java Program: public static void main (String args[ ])
The following shows the explanation individually:
public: it is the access specifier.
static: it allows main() to be called without instantiating a particular instance of a class.
void: it affirns the compiler that no value is returned by main().
main(): this method is called at the beginning of a Java program.
String args[ ]: args parameter is an instance array of class String
58. Define JRE i.e. Java Runtime Environment?
Java Runtime Environment is an implementation of the Java Virtual Machine which executes Java programs. It provides the minimum requirements for executing a Java application;
59. What is JAR file?
JAR files is Java Archive fles and it aggregates many files into one. It holds Java classes in a library. JAR files are built on ZIP file format and have .jar file extension.
60. What is a WAR file?
This is Web Archive File and used to store XML, java classes, and JavaServer pages. which is used to distribute a collection of JavaServer Pages, Java Servlets, Java classes, XML files, static Web pages etc.
61. Define JIT compiler?
It improves the runtime performance of computer programs based on bytecode.
62. What is the difference between object oriented programming language and object based programming language?
Object based programming languages follow all the features of OOPs except Inheritance. JavaScript is an example of object based programming languages
63. What is the purpose of default constructor?
The java compiler creates a default constructor only if there is no constructor in the class.
64. Can a constructor be made final?
No, this is not possible.
65. What is static block?
It is used to initialize the static data member, It is excuted before main method at the time of classloading.
66. Define composition?
Holding the reference of the other class within some other class is known as composition.
67. What is function overloading?
If a class has multiple functions by same name but different parameters, it is known as Method Overloading.
68. What is function overriding?
If a subclass provides a specific implementation of a method that is already provided by its parent class, it is known as Method Overriding.
69. Difference between Overloading and Overriding?
Method overloading increases the readability of the program. Method overriding provides the specific implementation of the method that is already provided by its super class parameter must be different in case of overloading, parameter must be same in case of overriding.
70. What is final class?
Final classes are created so the methods implemented by that class cannot be overridden. It can’t be inherited.
71. What is NullPointerException?
A NullPointerException is thrown when calling the instance method of a null object, accessing or modifying the field of a null object etc.
72. What are the 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 IO, 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.
73. How does multi-threading 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.
74. What invokes a thread’s run() method?
After a thread is started, via its start() method of the Thread class, the JVM invokes the thread’s run() method when the thread is initially executed.
75. Does it matter in what order catch statements for FileNotFoundException and IOException are written?
Yes, it does. The FileNoFoundException is inherited from the IOException. Exception’s subclasses have to be caught first.
76. 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.
77. Why Vector class is used?
The Vector class provides the capability to implement a growable array of objects. Vector proves to be very useful if you don’t know the size of the array in advance, or you just need one that can change sizes over the lifetime of a program.
78. How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8 characters?
Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character set uses only 7 bits, it is usually represented as 8 bits. UTF-8 represents characters using 8, 16, and 18 bit patterns. UTF-16 uses 16-bit and larger bit patterns.
79. What are Wrapper classes?
These are classes that allow primitive types to be accessed as objects. Example: Integer, Character, Double, Boolean etc.
80. What is the difference between a Window and a Frame?
The Frame class extends Window to define a main application window that can have a menu bar.
81. Which package has light weight components?
javax.Swing package. All components in Swing, except JApplet, JDialog, JFrame and JWindow are lightweight components.
82. 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.
83. What is the purpose of File class?
It is used to create objects that provide access to the files and directories of a local file system.
84. What is the difference between the Reader/Writer class hierarchy and the InputStream/OutputStream class hierarchy?
The Reader/Writer class hierarchy is character-oriented, and the InputStream/OutputStream class hierarchy is byte-oriented.
85. Which class should you use to obtain design information about an object?
The Class class is used to obtain information about an object’s design and java.lang.Class class instance represent classes, interfaces in a running Java application.
86. What is the difference between static and non-static variables?
A static variable is associated with the class as a whole rather than with specific instances of a class. Non-static variables take on unique values with each object instance.
87. What is Serialization and deserialization?
Serialization is the process of writing the state of an object to a byte stream. Deserialization is the process of restoring these objects.
88. Can you write a Java class that could be used both as an applet as well as an application?
Yes, just add a main() method to the applet.
89. What is the difference between Swing and AWT components?
AWT components are heavy-weight, whereas Swing components are lightweight. Heavy weight components depend on the local windowing toolkit. For example, java.awt.Button is a heavy weight component, when it is running on the Java platform for Unix platform, it maps to a real Motif button.
90. What’s the difference between constructors and other methods?
Constructors must have the same name as the class and can not return a value. They are only called once while regular methods could be called many times.
91. Is there any limitation of using Inheritance?
Yes, since inheritance inherits everything from the super class and interface, it may make the subclass too clustering and sometimes error-prone when dynamic overriding or dynamic overloading in some situation.
92. What’s the difference between the methods sleep() and wait()?
The code sleep(2000); puts thread aside for exactly two seconds. The code wait(2000), causes a wait of up to two second. A thread could stop waiting earlier if it receives the notify() or notifyAll() call. The method wait() is defined in the class Object and the method sleep() is defined in the class Thread.
93. When ArithmeticException is thrown?
The ArithmeticException is thrown when integer is divided by zero or taking the remainder of a number by zero. It is never thrown in floating-point operations.
94. What is the Collections API?
The Collections API is a set of classes and interfaces that support operations on collections of objects.
95. Does garbage collection guarantee that a program will not run out of memory?
Garbage collection does not guarantee that a program will not run out of memory. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection.
96. What is the difference between a break statement and a continue statement?
A break statement results in the termination of the statement to which it applies (switch, for, do, or while). A continue statement is used to end the current loop iteration and return control to the loop statement.
97. If a variable is declared as private, where may the variable be accessed?
A private variable may only be accessed within the class in which it is declared.
98. What is JVM ? Why is Java called the “Platform Independent Programming Language” ?
A Java virtual machine (JVM) is a process virtual machine that can execute Java bytecode. Each Java source file is compiled into a bytecode file, which is executed by the JVM. Java was designed to allow application programs to be built that could be run on any platform, without having to be rewritten or recompiled by the programmer for each separate platform. A Java virtual machine makes this possible, because it is aware of the specific instruction lengths and other particularities of the underlying hardware platform.
99. What is the Difference between JDK and JRE ?
The Java Runtime Environment (JRE) is basically the Java Virtual Machine (JVM) where your Java programs are being executed. It also includes browser plugins for applet execution. The Java Development Kit (JDK) is the full featured Software Development Kit for Java, including the JRE, the compilers and tools (like JavaDoc, and Java Debugger), in order for a user to develop, compile and execute Java applications.
100. Explain the available thread states in a high-level.
During its execution, a thread can reside in one of the following states:
Runnable: A thread becomes ready to run, but does not necessarily start running immediately.
Running: The processor is actively executing the thread code.
Waiting: A thread is in a blocked state waiting for some external processing to finish.
Sleeping: The thread is forced to sleep.
Blocked on I/O: Waiting for an I/O operation to complete. Blocked on Synchronization: Waiting to acquire a lock.
Dead: The thread has finished its execution.
101. What is the primary benefit of Encapsulation?
The main benefit of encapsulation is the ability to modify our implemented code without breaking the code of others who use our code. With this Encapsulation gives maintainability, flexibility and extensibility to our code.
102. What is an Interface?
An interface is a collection of abstract methods. A class implements an interface, thereby inheriting the abstract methods of the interface.
103. Give some features of Interface?
It includes: Interface cannot be instantiated An interface does not contain any constructors. All of the methods in an interface are abstract.
104. Define Packages in Java?
A Package can be defined as a grouping of related types(classes, interfaces, enumerations and annotations ) providing access protection and name space management.
105. Why Packages are used?
Packages are used in Java in-order to prevent naming conflicts, to control access, to make searching/locating and usage of classes, interfaces, enumerations and annotations, etc., easier.
106. What do you mean by Multithreaded program?
A multithreaded program contains two or more parts that can run concurrently. Each part of such a program is called a thread, and each thread defines a separate path of execution.
107. What are the two ways in which Thread can be created?
Thread can be created by: implementing Runnable interface, extending the Thread class.
108. What is an applet?
An applet is a Java program that runs in a Web browser. An applet can be a fully functional Java application because it has the entire Java API at its disposal.
109. An applet extend which class?
An applet extends java.applet.Applet class.
110. Explain garbage collection in Java?
It uses garbage collection to free the memory. By cleaning those objects that is no longer reference by any of the program.