Question

/**

* Interface for a set data type that supports adding, removing and contains operations.

* @param <T> the type parameter for the elements of the set

*/

interface SetADT<T> {

/**

* Add a new element to the set.

* @param el the new element to add to the set

* @return true if the element has been added to the set, false if it was already in the set

* @throws IllegalArgumentException if the new element passed to the method is null

*/

public boolean add(T el);

/**

* Return true if the element is in the set, false otherwise.

* @param el the element to check for

* @return true if the element is in the set, false if it is not

*/

public boolean contains(T el);

/**

* Remove element from the set.

* @param el the element to remove from the set

* @return true if the element has been removed, false otherwise (if it was not in the set)

*/

public boolean remove(T el);

}

public class MyHashSet<T> implements SetADT<T>{

  
/**
* Add a new element to the set.
* @param el the new element to add to the set
* @return true if the element has been added to the set, false if it was already in the set
* @throws IllegalArgumentException if the new element passed to the method is null
*/
@Override
public boolean add(T el) {
// TODO Auto-generated method stub
return false;
}
    /**
* Return true if the element is in the set, false otherwise.
* @param el the element to check for
* @return true if the element is in the set, false if it is not
*/
@Override
public boolean contains(T el) {
// TODO Auto-generated method stub
return false;
}
  

/**
* Remove element from the set.
* @param el the element to remove from the set
* @return true if the element has been removed, false otherwise (if it was not in the set)
*/
@Override
public boolean remove(T el) {
// TODO Auto-generated method stub
return false;
}

  
public static void main (String[] args) {
  
  
}
}

1. MyHashSet must be a generic class and implement the SetADT interface and provide a constructor with no arguments. You do not have to implement a constructor yourself and can use the default one.
2. Implement all three functions of the SetADT interface using Java's java.util.Hashtable (Links to an external site.) class. Refer to the comments in the SetADT.java file for details on what the methods should do. Note that for java.util.Hashtable you will need two type parameters (and you will need to add and remove object pairs from the table). You can use the same type for both parameters (your set type parameter), and insert every element twice (as a pair) into the hash table. The class java.util.Hashtable does neither support null keys nor null values. You don't have to support those in your set implementation either (you don't have to worry about the user passing null parameters to your methods, the methods of java.util.Hashtable take care of this and will throw NullPointerExceptions in these cases).
3. For each of the methods, add a small demo to the main method of that demonstrates their functionality (the main method must call each of them at least once).

Answer 1

import java.util.LinkedHashMap;


interface setADT<T>{
        public boolean add(T el);
        public boolean contains(T el);
        public boolean remove(T el);
}
public class MyHashSet<T> implements setADT<T> {
        //I am using LinkedHashMap HashTable data structure to store the values.
        //HashTable data structure.which can be used to store the elements
        //and implements the functionalities of set.
        LinkedHashMap<T,T> hash = new LinkedHashMap();

        

        @Override
        public boolean add(T el) {
                // TODO Auto-generated method stub
                //hash.get(el) will returnss null if el not present in it otherwise value corresponding to key in HashTable.
                //if el is not in hash then we add el to set and returns true.otherwise false;
                if(hash.get(el) == null) {
                        hash.put(el,el);
                        return true;
                }
                return false;
        }

        @Override
        public boolean contains(T el) {
                // TODO Auto-generated method stub
                //if el in hash then condition is false not of false is true.so it will returns true if value present in it.
                //otherwise false.
                return !(hash.get(el) == null);
        }

        @Override
        public boolean remove(T el) {
                // TODO Auto-generated method stub
                //if el in hash it will removes from hash then returns true.other wise false.
                if(hash.get(el) != null) {
                        hash.remove(el);
                        return true;
                }
                return false;
        }
        
        
        public static void main(String[] args) {
                //test cases
                //object creation.
                setADT<Integer> o = new MyHashSet<Integer>();
                System.out.println(o.add(10));
                System.out.println(o.add(20));
                System.out.println(o.add(50));
                System.out.println(o.remove(10));
                System.out.println(o.contains(20));
                

        }

}

/*
 * output
  true
true
true
true
true

 * 
 */