Chettinad College of Engineering & Technology Department of Information Technology Internal Examination II (Answer Key)

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1 Chettinad College of Engineering & Technology Department of Information Technology Internal Examination II (Answer Key) Branch & Section : B.Tech-IT / III Date: Semester : III Year V Sem Max. Marks: 50 Subject Code & Title : IT2301 Java Programming Staff In-charge: Mrs P.Susila Part A (5 x 2 = 10 marks) Answer all the Questions 1. Differentiate a vector and array in Java. A vector is a dynamic array, whose size can be increased, where as an array size cannot be changed. Reserve space can be given for vector, whereas for arrays cannot. A vector is a class where as an array is not. Vectors can store any type of objects, where as an array can store only homogeneous values. 2. What is a package? How to import a single package? A package is a group of similar types of classes, interfaces and sub-packages. The grouping is usually done according to functionality. In fact, packages act as containers for classes. Package can be categorized in two form, built-in package and user-defined package. There are many built-in packages such as java, lang, awt, javax, swing, net, io, util, sql etc. 3. What is the difference between String and StringBuffer? String is immutable (once created cannot be changed) object. The object created as a String is stored in the Constant String Pool. String once assigned cannot be changed. StringBuffer is mutable means one can change the value of the object. The object created through StringBuffer is stored in the heap. StringBuffer is faster when performing concatenations. This is because when you concatenate a String, you are creating a new object (internally) every time since String is immutable. String Buffer can be converted to the string by using tostring() method. 4. What is object cloning? When a copy of a variable is made, the original and the copy objects have references to the same object. This means a change to either variable also affects the other. 1

2 Cloning is about creating the copy of original object. By default, java cloning is field by field copy. So, JVM when called for cloning, do following things: 1) If the class has only primitive data type members then a completely new copy of the object will be created and the reference to the new object copy will be returned. 2) If the class contains members of any class type then only the object references to those members are copied and hence the member references in both the original object as well as the cloned object refer to the same object. Types of Cloning: 1. Shallow Cloning Default Cloning method 2. Deep Cloning To do cloning a class must 1. Implement the Cloneable interface, and 2. Redefine the Clone method with the public access modifier. 5. How does the declaration of a local inner class differ from the declaration of an anonymous inner class? Local Inner Class: A class that is created inside a method is known as local inner class. If you want to invoke the methods of local inner class, you must instantiate this class inside the method. Their scope is always restricted to the block in which they are declared. Anonymous Inner Class: When using local inner classes, we can create any number of Objects for the Inner Class. If to make only a single object of a class, no need to give the class name. Such a class is called an Anonymous Inner Class. Here, Interface can be used, the inner class implements that interface. Outer Class s methods define the implementation of the inner class within its own member function. Part B (40 marks) Answer All the Questions 6. a. Write a java program to maintain the books details like BookId, accession number; book name, author, publication in books package and keep the journal details such as journal id; journal name; in journal package in main class use these two packages details for staff and student classes and display the books and journals information as requested by the user. (16) Packages Packages are java s way of grouping a variety of classes and / or interfaces together. The grouping is usually done according to functionality. In fact, packages act as containers for classes. Benefits of Packages The classes contained in the packages can be easily reused. In packages, classes can be unique compared with classes in other packages. That is, two classes in two different packages can have the same name. They 2

3 may be referred by their fully qualified name, comprising the package name and class name. Package provide a way to hide classes thus preventing other programs or package from accessing classes that are meant for internal use only. Packages also provide a way for separating design from coding. First we can design classes and decide their relationships, and then we can implement the java code needed for the methods. It is possible to change the implementation of any method without affecting the rest of the design. Types of Packages Java packages are therefore classified into two types. Pre defined packages (Java API Packages) User defined packages Sample Example Program package PackageBook; import java.io.*; public class Book int book_no, book_id, book_pages; public Book(int a, int b, int c) book_no=a; book_id=b; book_pages=c; public void BookInfo() System.out.println("The Book No "+book_no); System.out.println("The Book Id "+book_id); System.out.println("The Book Pages "+book_pages); import java.io.*; import PackageBook.Book; public class BookReader public static void main(string[] args) Book b=new Book(10, 15, 90); b.bookinfo(); 3

4 (Or) b. How to declare and initialize a string in java and also explain the different string handling functions with suitable examples. (16) String: Java s String type called String, is not a Simple Type, nor is it simply an array of characters. Rather String defines an Object. The String type is used to declare string variable. Java Strings are sequences of Unicode Characters. Use an object of type string as an argument to println(); String str = Welcome to JAVA ; System.out.println(str); Java has methods to compare two strings, search for a substring, concatenate two strings, and change the case of letters within a String. String object has been created, you cannot change the characters that comprise that string. String Constructors: The String class supports several constructors. To create an empty string call the default constructor. String str = new String(); Initialize the values through array of characters. char ch[] = a, b, c ; String str = new String(ch); o/p: abc 1. Subrange: String(char ch[], int start,int numchar); char ch[] = a, b, c, d, e,f ; String s = new String(ch,2,3); o/p: cde 2. String copy: String(String strobj); char ch[] = J, A, V, A ; String s1 = new String(ch); String s2 = new String(s1); System.out.println(s1); O/P: JAVA System.out.println(s2); O/P: JAVA 3. ASCII char: String (byte asciichars[]); String(byte asciichars[], int start, int numchars); byte ascii[] =65,66,67,68,69,70; String s1 = new String(ascii); System.out.println(s1); O/P: ABCDEF String s2 = new String(ascii,2,3); O/P: CDE 4

5 SPECIAL STRING OPERATIONS 1. Automatic creation of new String instances from string literals. 2. Concatenation of multiple String object by used of the + operators 3. Conversion of other data types to a string representation. Write some example programs for String class using methods like length(), concat(), charat(), getchars(), msg.getbytes(), tochararray(), equals() and equalsignorecase(), startswith() and endswith(),equals() Versus ==, compareto(), modifying a string like substring(), replace(), trim(), touppercase() and tolowercase(), etc., and StringBuffer methods. 7. a. i) Explain about JavaDoc comments. (8) JavaDoc Comments: Javadoc is a tool which comes with JDK and it is used for generating Java code documentation in HTML format from Java source code which has required documentation in a predefined format. The Java language supports three types of comments: /* text */ - The compiler ignores everything from /* to */. // text - The compiler ignores everything from // to the end of the line. /** documentation */ - This is a documentation comment and in general its called doc comment. The JDK javadoc tool uses doc comments when preparing automatically generated documentation. Types of Comments Class Comments - /*.*/ and /* * */ Method @throws Field Comments Data Members - /* * */ General @since. /** * The HelloWorld program implements an application that * simply displays "Hello World!" to the standard output. * John */ public class HelloWorld public static void main(string[] args) /* Prints Hello, World! on standard output. */ System.out.println("Hello World!"); 5

6 The JavaDoc Tags: Give explanation and syntax for the @since, ii) Consider a class Student with attributes name and subject. Write a java program to create and clone instances of Student class. (8) Object Cloning in Java: When a copy of a variable is made, the original and the copy objects have references to the same object. This means a change to either variable also affects the other. Student original = new Student(1001, CCET ); Student copy = original; // taking copy copy.dept_change( CSE ); // Original Objects also changed In order to copy an old object into another new object which should not refer to the old object but the values has to copied to a new reference then use the clone method. The object cloning is a way to create exact copy of another object without affecting one another. Student copy = original.clone(); copy.dept_change( CSE ); //Original unchanged The java.lang.cloneable interface must be implemented by the class whose object clone we want to create. If we don't implement Cloneable interface, clone() method generatesclonenotsupportedexception. The clone() method is a protected method defined in the Object class. Syntax of the clone() method is as follows: Syntax: protected Object clone() throws CloneNotSupportedException Types of Cloning: 1. Shallow Cloning Default Cloning method 2. Deep Cloning To do cloning a class must Implement the Cloneable interface, and Redefine the Clone method with the public access modifier. Program for Shallow Copy class Subject String name; String getname() 6

7 return name; void setname(string s) name = s; Subject(String s) name = s; class Student implements Cloneable //Contained object Subject subj; String name; Student(String s, String sub) name = s; subj = new Subject(sub); String getname() return name; void setname(string s) name = s; Subject getsubj() return subj; public Object clone() //shallow copy try return super.clone(); catch (CloneNotSupportedException e) 7

8 return null; public class ShallowCopy public static void main(string[] args) //Original Object Student stud = new Student("John", "Algebra"); System.out.println("Original Object: " + stud.getname() + " - " + stud.getsubj().getname()); //Clone Object Student clonedstud = (Student)stud.clone(); System.out.println("Cloned Object: " + clonedstud.getname() + " - " + clonedstud.getsubj().getname()); stud.setname("dan"); stud.getsubj().setname("physics"); System.out.println("Original Object after it is updated: " + stud.getname() + " - " + stud.getsubj().getname()); System.out.println("Cloned Object after updating original object: " + clonedstud.getname() + " - " + clonedstud.getsubj().getname()); (Or) b. What is exception handling in java? Why it is used? Write a java code to simulate the way a stack mechanism works with exception handling, throwing and dealing with exceptions such as stack is full(if you want to add more elements into the stack) or stack is empty (if you want to pop elements from the stack). (16) Exception An Exception is a condition that is caused by a run time error in the program. Exception Handling If the exception object is not caught and handled properly, the compiler will display an error message and will terminate the program. If we want the program to continue with the execution of the remaining appropriate message for taking corrective actions. This task is known as exception handling. 8

9 All Exception types are subclasses of the built in class Throwable. Throwable is at the top of the exception class hierarchy Exception Handling Mechanism The purpose of the exception handling mechanism is to provide means to detect and report an exceptional circumstance, so that appropriate action can be taken. The Error Handling code that performs the following tasks: 1. Find the problem (Hit the Exception) 2. Inform that an error has occurred (Throw the exception) 3. Receive the error information (Catch the exception) 4. Take corrective actions (Handle the exception) Program import java.util.linkedlist; class Stackimp implements Mystack int stack[]=new int[n]; int top=-1; public void push() try DataInputStream dis=new DataInputStream(System.in); if(top==(n-1)) System.out.println("overflow"); return; else System.out.println("enter element"); int ele=integer.parseint(dis.readline()); stack[++top]=ele; catch(exception e) System.out.println(e); public void pop() 9

10 class stackadt if(top<0) System.out.println("underflow"); return; else int popper=stack[top]; top--; System.out.println("popped element "+popper); public void peek() if(top<0) System.out.println("underflow"); return; else int popper=stack[top]; System.out.println("popped element "+popper); public void display() if(top<0) System.out.println("empty"); return; else String str=""; for(int i=0;i<=top;i++) str=str+" "+stack[i]; System.out.println("elements are "+str); 10

11 public static void main(string arg[])throws IOException DataInputStream dis=new DataInputStream(System.in); int ch1=0; do System.out.println("Enter your choice for 1.Stack in Array 2.Stack in linkedlist 3.Exit"); ch1=integer.parseint(dis.readline()); switch(ch1) case 1: int ch2=0; Stackimp stk=new Stackimp(); do System.out.println("Stack in Array"); System.out.println("Enter your choice for 1.push 2.pop 3.peek 4.display 5.exit"); ch2=integer.parseint(dis.readline()); switch(ch2) case 1:stk.push(); case 2:stk.pop(); case 3:stk.peek(); case 4:stk.display(); case 5: while(ch2<5); case 2: int ch3=0; stacklist st=new stacklist(); do System.out.println("Stack in LinkedList"); System.out.println("enter your choice for 1.push 2.pop 3.peek 4.display 5.exit"); ch3=integer.parseint(dis.readline()); 11

12 switch(ch3) case 1:st.push(); case 2:st.pop(); case 3:st.peek(); case 4:st.display(); case 5: while(ch3<5); case 3:System.exit(0); while(ch1<=3); 8. What is meant by stream? What are the types of streams and classes? Explain in detail. (8) Stream A Stream is a sequence of data. It is composed of bytes. It is basically a channel on which the data flow from sender to receiver. The Java I/O means Java Input/Output. It is provided by the java.io package. This package has an InputStream and OutputStream. Java InputStream is defined for reading the stream, byte stream and array of byte stream. An input object that reads the stream of data from a file is called input stream and the output object that writes the stream of data to a file is called output stream. Java implements streams within the classes that are defined in java.io package. Types of streams Character Stream Byte Stream Character Stream The two super classes in character stream are Reader and Writer. Byte Stream The two super clasess in byte stream are InputStream and OutputStream from which most of the other classes are derived. 12

13 Some important Character Stream classes: Reader, Writer, BufferedReader, BufferedWriter, FileReader, FileWriter, InputStreamReader, OutputStreamReader, PrintWriter. Some important Byte Stream classes: InputStream, OutputStream, BufferedInputStream, BufferedOutputStream, DataInputStream, DataOutputStream, FileInputStream, FileOutputStream, PrintStream. Write example program using some of the above classes Sample Program import java.io.*; public class BRReadLines public static void main(string args[]) throws IOException BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); String str; System.out.println("Enter lines of text."); System.out.println("Enter 'end' to quit."); do str = br.readline(); System.out.println(str); while(!str.equals("end")); Faculty In-charge HOD/IT 13

copy.dept_change( CSE ); // Original Objects also changed

copy.dept_change( CSE ); // Original Objects also changed UNIT - III Topics Covered The Object class Reflection Interfaces Object cloning Inner classes Proxies I/O Streams Graphics programming Frame Components Working with 2D shapes. Object Clone Object Cloning