Question

In Java, write an equals method suitable for the DoubleLinkedSequence class.

The method takes a single argument, a DoubleLinkedSequence (or an Object) and returns true if both collections contain the same values in the same order (in sequences, order matters).  

Make sure your equals method is efficient and exits as soon as they are determined to be not equal.  

Note:  The data structure contains doubles, this is not about doubly?linked lists.

Answer 1

Please find the equals() method in Java below:-

 /*
 * Returns true if linked lists a and b are identical, otherwise false
 */
public boolean equals(ValidateLinkedList listb) {
   Node a = this.head, b = listb.head;
   while (a != null && b != null) {
      if (a.getElement() != b.getElement())
         return false;

      /*
       * If we reach here, then a and b are not null and their data is
       * same, so move to next nodes in both lists
       */
      a = a.getNext();
      b = b.getNext();
   }

   // If linked lists are identical, then 'a' and 'b' must
   // be null at this point.
   return (a == null && b == null);
}

Please find the entire Java program where equals() is implemented:-

1. Node.java

public class Node {

private double element;

private Node next;

public Node(double element, Node next) {

super();

this.element = element;

this.next = next;

}

public Node(double element) {

super();

this.element = element;

}

public double getElement() {

return element;

}

public Node getNext() {

return next;

}

public void setNext(Node next) {

this.next = next;

}

}

2. DoubleLinkedSequence.java

public class DoubleLinkedSequence {

Node head; // head of list

/*

* Returns true if linked lists a and b are identical, otherwise false

*/

public boolean equals(DoubleLinkedSequence listb) {

Node a = this.head, b = listb.head;

while (a != null && b != null) {

if (a.getElement() != b.getElement())

return false;

/*

* If we reach here, then a and b are not null and their data is

* same, so move to next nodes in both lists

*/

a = a.getNext();

b = b.getNext();

}

// If linked lists are identical, then 'a' and 'b' must

// be null at this point.

return (a == null && b == null);

}

/* UTILITY FUNCTIONS TO TEST fun1() and fun2() */

/*

* Given a reference (pointer to pointer) to the head of a list and an int,

* push a new node on the front of the list.

*/

void push(double new_data) {

/*

* 1 & 2: Allocate the Node & Put in the data

*/

Node new_node = new Node(new_data);

/* 3. Make next of new Node as head */

new_node.setNext(head);

/* 4. Move the head to point to new Node */

head = new_node;

}

/* Drier program to test above functions */

public static void main(String args[]) {

DoubleLinkedSequence llist1 = new DoubleLinkedSequence();

DoubleLinkedSequence llist2 = new DoubleLinkedSequence();

DoubleLinkedSequence llist3 = new DoubleLinkedSequence();

/*

* The constructed linked lists are : llist1: 3->2->1 llist2: 3->2->1

*/

llist1.push(1.90);

llist1.push(2.89);

llist1.push(3.76);

llist2.push(1.90);

llist2.push(2.89);

llist2.push(3.76);

llist3.push(1.90);

llist3.push(3.76);

llist3.push(2.89);

if (llist1.equals(llist2))

System.out.println("LinkedList1 and LinkedList2 are Identical ");

else

System.out.println("LinkedList1 and LinkedList2 are Different ");

if (llist1.equals(llist3))

System.out.println("LinkedList1 and LinkedList3 are Identical ");

else

System.out.println("LinkedList1 and LinkedList3 are Different ");

}

}

The output is attached below:-

Please let me know in case of any clarifications required. Thanks!