java programming exercises with solutions

 java programming exercises with solutions

Define a class named The message that contains an instance variable of type String named text that stores any textual content for the Message. Create a method named toString that returns the text field and also include a method to set this value.

Next, define a class for SMS that is derived from Message and includes instance variables for the recipientContactNo. Implement appropriate accessor and mutator methods. The body of the SMS message should be stored in the inherited variable text. Redefine the toString method to concatenate all text fields.

Similarly, define a class for Email that is derived from Message and includes an instance variable for the sender, receiver, and subject.  The textual contents of the file should be stored in the inherited variable text. Redefine the toString method to concatenate all text fields.

Create sample objects of type Email and SMS in your main method. Test your objects by passing them to the following subroutine that returns true if the object contains the specified keyword in the text property.

public static boolean ContainsKeyword(Message  messageObject,  String  keyword) {
        if  (messageObject.toString().indexOf(keyword,0)  >=  0)
        return  true;

        return  false;
        }

Finally, include a method to encode the final message  “This is  Java” using an encoding scheme, according to which, each character should be replaced by the character that comes after it. For example, if the message contains character B orb, it should be replaced by C or c accordingly, while Z or z should be replaced with an A  or a. If the final message is “This is Java”, then the encoded message should be “UijtjtKbwb”.

Message.java

class  Message{

    //  instance  variable  text String  text;
    String text;

    //  constructor
    public  Message(String  text)  {
        this.text  =  text;
    }

    //  setter
    public  void  setText(String  text)  {
        this.text  =  text;
    }

    //  toString  method  returns  text 
    public  String  toString() {
        return  this.text;
    }
}

SMS.java

//  class  SMS  extending  Message  class
public class SMS extends Message {
    //  instance  variable String  recipientContactNo;
    String recipientContactNo;

    //  constructor
    public  SMS(String  text,String  recipientContactNo) {
        super(text);
        this.recipientContactNo  =  recipientContactNo;
    }

    //  getter  method
    public  String  getReceiptContactNo()  {
        return  recipientContactNo;
    }

    //  setter  method
    public  void  setReceiptContactNo(String  receiptContactNo)  {
        this.recipientContactNo  =  receiptContactNo;
    }

    //  toString  method  returns  text  concatenated  with  recipientContactNo 
    public  String  toString() {
        return  super.toString()+"  "+this.recipientContactNo;
    }
}

Email.java

//  email  class  extending  Message  class 
class Email extends Message {

    // instance variables
    String sender, reciever, subject;

    // constructor
    public Email(String sender, String reciever, String subject, String text) {
        super(text);
        this.sender = sender;
        this.reciever = reciever;
        this.subject = subject;
    }

    // toString() method returns text,sender,reciever,subject
    public String toString() {
        return super.toString() + "  " + this.sender + "  " + this.reciever + "  " + this.subject;
    }
}

Main.java

// main
class public class Main {

    // containsKeywordmethod 
    public static boolean ContainsKeyword(Message messageObject, String keyword) {
        if (messageObject.toString().indexOf(keyword, 0) >= 0) return true;

        return false;
    }

    // encode method converts each character in a string to its successive character    
    public static void encode(Message messageObject)  {
        String msg = messageObject.text;
        String encoded = "";

        for (char c: msg.toCharArray()) {
            if (!(c == ' '))
                encoded += Character.toString((char)(((c - 'a' + 1) % 26) + 'a'));
        }
        System.out.println(encoded);
    }

    //main method 
    public static void main(String[] args) {

        // sample email object 
        Email email = new Email("Me", "you", "Question", "Answered");
        // sample SMS object 
        SMS sms = new SMS("Hey", "909099909");

        // testing containsKeyword method 
        System.out.println("Testing ConatinsKeyword method..\n");
        System.out.println(ContainsKeyword(email, "Me"));
        System.out.println(ContainsKeyword(sms, "Hai"));

        // testing encode method. 
        System.out.println("Testing encode method");

        encode(new Message("This is Java"));
    }
}