RiddleClass
Riddle class from Chapter 1, which is summarized in the UML diagram in Figure 2.4.1. A Riddle has two attributes, question and answer. Each of these variables stores a String. It contains three methods, the Riddle() constructor, the getQuestion() and getAnswer() methods.
Riddle class.question and answer are designated as private(Riddle(), getQuestion() and getAnswer() methods are designated as public (Riddle class:private instance variables and defines the three public methods listed in the UML diagram.Riddle class.public class Riddle {
private String question; //Instance variables
private String answer;
public Riddle(String q, String a) { // Constructor
question = q;
answer = a;
} // Riddle constructor
public String getQuestion() { // Instance method
return question;
} // getQuestion()
public String getAnswer() { // Instance method
return answer;
} //getAnswer()
} //Riddle class
private and public modifiers are known as access modifiers. They control access to an object’s elements, such as its variables or methods, by other objects — preventing access to private elements and permitting access to the public elements. Note also that the Riddle class itself is declared public, which allows access to its objects through its public variables and methods.private so that they cannot be directly accessed by other objects. This is an example of information hiding.public methods can be used by other objects to interact with the object. The public methods and variables of an object make up its interface.Riddle class defines the type of information (attributes) that each Riddle object has, but it doesn’t contain any actual values. It defines the methods (operations) that each Riddle object can perform, but it doesn’t actually perform the methods.RiddleUser Class
Riddle we need to define a main() method, which can be defined either within the Riddle class itself or in a second class.Riddle's task is just to manage simple riddles.
RiddleUser class.RiddleUser and one or more Riddles. The relationship between them, represented by a one-way “Uses” arrow,is that the RiddleUser will create a Riddle instance and use its methods to display a riddle for the user.
RiddleUser and Riddle classes. The RiddleUser class will use one or more objects of the Riddle class.RiddleUser) and the computation (Riddle). Each type of object manages its own task and they work together to solve a problem.Riddle Instances
RiddleUser class, which serves as a very simple user interface. It creates two Riddle objects, named riddle1 and riddle2. It then asks each object to request each riddle’s question and answer and displays them on the console.RiddleUser class.public class RiddleUser
{
public static void main(String argv[])
{ Riddle riddle1 = new Riddle(
"What is black and white and red all over?",
"An embarrassed zebra.");
Riddle riddle2 = new Riddle(
"What is black and white and read all over?",
"A newspaper.");
System.out.println("Here are two riddles:");
System.out.println(riddle1.getQuestion());
System.out.println(riddle2.getQuestion());
System.out.println("The answer to the first riddle is:");
System.out.println(riddle1.getAnswer());
System.out.println("The answer to the second is:");
System.out.println(riddle2.getAnswer());
} // main()
} // RiddleUser
RiddleUser’s main() method. The following statements use the Riddle() constructor to create, or instantiate, two instances of the Riddle class:Riddle riddle1 = new Riddle(
"What is black and white and red all over?",
"An embarrassed zebra.");
Riddle riddle2 = new Riddle(
"What is black and white and read all over?",
"A newspaper.");
String s that serve as the values of their two instance variables. Each object has its own question and its own answer, and each object has its own unique name, riddle1 and riddle2.Riddles
Riddle instances with values assigned to their question and answer instance variables, we can ask each riddle to tell us either of its values. The following expression is an example of a method call:riddle1.getQuestion()
String value that is stored in the question instance variable of riddle1.riddle1’s question, we can embed this method call within a println() statementSystem.out.println(riddle1.getQuestion());
System.out object to execute its println() method, which displays the string given to it by riddle1 on the console. Thus, the output produced by this statement will beWhat is black and white and red all over?
