Question

The purpose of this problem is to practice using a generic Jar class.

write in drjava

Create a generic class, called Jar, with a type parameter that simulates drawing an item at random out of a Jar. For example the Jar might contain Strings representing names written on a slip of paper, or the Jar might contain integers representing a random drawing for a lottery. Include the following methods in your generic class, along with any other methods you’d like:

• an add( ) method that allows the user to add one object of the specified type
• an isEmpty( ) method (returns true if the Jar is empty, otherwise returns false)
• a drawItem( ) method that randomly selects an object from the Jar and returns it. Return null if the Jar is empty. Do not delete the selected item. (see Note below)
• a toString( ) method (returns a String containing the Jar’s contents)

Your Jar class with need an array of size 10 to hold the objects in the Jar, and a count variable to maintain a count of how many objects are actually in the Jar.

In the driver file that tests your class create 2 Jars, one with the names of 6 of your friends, the other with numbers between 2 and 8 inclusive representing the number of hours you will spend partying tonight with 3 of your friends.

Use the add( ) method to populate the 2 Jars, and the drawItem( ) method for each Jar to determine    i) which 3 friends you will invite out to party with   and   ii) how many hours of partying you and your friends will do.

Test the isEmpty and toString methods as well for the 2 Jars.

Note:

public int nextInt(int bound) in java.util.Random returns a random int value between 0 (included) and the specified value, bound, (excluded).

Answer 1

// Jar.java
import java.util.Random;

public class Jar<T> {
  
   private T items[];
   private int count;
  
   // constructor to create an empty jar of maximum 10 items
   public Jar()
   {
       items = (T[]) new Object[10];
       count = 0;
   }

   // method to add an item in the jar
   public void add(T value)
   {
       // check if jar has room, then add
       if(count < items.length)
       {
           items[count] = value;
           count++;
       }
   }
  
   // method that returns if the jar is empty or not
   public boolean isEmpty()
   {
       return(count == 0);
   }
  
   // method to return a randomly selected item from the jar (doesn't remove the selected item)
   public T drawItem()
   {
       if(isEmpty())
           return null;
      
       Random ran = new Random();
       int idx = ran.nextInt(count);
       return items[idx];
   }
  
   // returns string representation of the jar items
   public String toString()
   {
      
       if(isEmpty())
           return "Empty Jar";
          
       String jarStr = "";
       for(int i=0;i<count;i++)
           jarStr += items[i].toString()+"\n";
       return jarStr;
   }
}
//end of Jar.java

//JarDriver.java

public class JarDriver {
      
   public static void main(String[] args) {
      
       // create 2 jars
       Jar<String> friendsJar = new Jar<String>();
       Jar<Integer> hoursJar = new Jar<Integer>();
       // add elements to both jar
       friendsJar.add("John");
       friendsJar.add("Kelly");
       friendsJar.add("Michelle");
       friendsJar.add("Sheldon");
       friendsJar.add("Mike");
       friendsJar.add("Shaun");
      
       hoursJar.add(2);
       hoursJar.add(4);
      
       // draw 3 items from friendsJar
       System.out.println("The 3 friends invited to party : ");
       System.out.println(friendsJar.drawItem());
       System.out.println(friendsJar.drawItem());
       System.out.println(friendsJar.drawItem());
       // draw one item from hoursJar
       System.out.println("Number of hours of partying : "+hoursJar.drawItem());
      
       // display the items in friendsJar and hoursJar
       System.out.println("\nFriends : \n"+friendsJar);
       System.out.println("Hours : \n"+hoursJar);
      

   }

}
//end of JarDriver.java

Output:

The 3 friends invited to party Shaun John Mike Number of hours of partying 2 Friends John Kelly Michelle Sheldon Mike Shaun Hours 2 4.