Question

I need help this Lab

Look at the linked articles and video to learn about linked lists.

Assignment

The code consists of three files that implement and use a simple linked list. The code was written in early Java style using the Object class in order to allow the linked list to be a list of objects of any type. While the code works, it is not type safe. Refactor the code to use Java Generics. You will need to change the Main class to create a linked list of Strings in the list1() method and a linked list of Integers in the list2() method.

You’ll then need to make appropriate modifications to the other two Java files so that they use Java Generics.

Do NOT use the built-in Java LinkedList class.

Additional Information

After you have completed and thoroughly tested your changes, zip the entire project and submit the zipped project file via

Coding:

package home;

public class Main {

    public static void main(String[] args) {
        list1();
        list2();
    }

    // Use linked list with Strings
    public static void list1() {
        LinkedList llist = new LinkedList();
        llist.addFirst("one");
        llist.addLast("two");
        llist.addLast("three");
        llist.addFirst("zero");
        llist.addLast("xxxx");
        llist.addFirst("yyyyy");
        llist.deleateLast();
        llist.deleteFirst();
        System.out.println(llist);
        llist.deleteFirst();
        llist.deleateLast();
        llist.deleteFirst();
        llist.deleateLast();
        System.out.println(llist);
    }

    // Use linked list with Integers
    public static void list2() {
        LinkedList llist = new LinkedList();
        llist.addFirst(1);
        llist.addLast(2);
        llist.addLast(3);
        llist.addFirst(0);
        llist.addLast(142);
        llist.addFirst(-97);
        llist.deleateLast();
        llist.deleteFirst();
        System.out.println(llist);
        llist.deleteFirst();
        llist.deleateLast();
        llist.deleteFirst();
        llist.deleateLast();
        System.out.println(llist);
    }
}

package home;

public class LinkedList {
    private Node head;

    public LinkedList() {
        head = null;
    }

    public void addFirst(Object content) {
        Node ptr = head;
        head = new Node(content,ptr);
    }

    public void addLast(Object content) {
        Node last = new Node(content,null);
        if (head == null) {
            head = last;
        } else {
            Node ptr = head;
            while(ptr.getNext() != null) {
                ptr = ptr.getNext();
            }
            ptr.setNext(last);
        }
    }

    public boolean deleteFirst() {
        if (head == null) {
            return false;
        } else {
            head = head.getNext();
            return true;
        }
    }

    public boolean deleateLast() {
        if (head == null) {
            return false;
        }
        else if (head.getNext() == null) {
            head = null;
            return true;
        } else {
            Node ptr = head;
            while (ptr.getNext().getNext() != null) {
                ptr = ptr.getNext();
            }
            ptr.setNext(null);
            return true;
        }
    }

    public Node getHead() {
        return head;
    }

    public String toString() {
        String str;
        if (head == null) {
            str = "<empty>";
        } else {
            Node ptr = head;
            str = "("+ptr.getContent().toString()+")";
            while(ptr.getNext() != null) {
                str = str + "->";
                ptr = ptr.getNext();
                str = str + "(" + ptr.getContent().toString() + ")";
            }
        }
        return str;
    }
}

package home;

public class Node {
    private Object content;
    private Node next;

    public Node(Object content, Node next) {
        this.content = content;
        this.next = next;
    }

    public Object getContent() {
        return content;
    }

    public void setContent(Object content) {
        this.content = content;
    }

    public Node getNext() {
        return next;
    }

    public void setNext(Node next) {
        this.next = next;
    }
}

Answer 1

Main.java

public class Main {

    public static void main(String[] args) {
        list1();
        list2();
    }

    // Use linked list with Strings
    public static void list1() {
        LinkedList <String> llist = new LinkedList <>();
        llist.addFirst("one");
        llist.addLast("two");
        llist.addLast("three");
        llist.addFirst("zero");
        llist.addLast("xxxx");
        llist.addFirst("yyyyy");
        llist.deleateLast();
        llist.deleteFirst();
        System.out.println(llist);
        llist.deleteFirst();
        llist.deleateLast();
        llist.deleteFirst();
        llist.deleateLast();
        System.out.println(llist);
    }

    // Use linked list with Integers
    public static void list2() {
        LinkedList <Integer> llist = new LinkedList <>();
        llist.addFirst(1);
        llist.addLast(2);
        llist.addLast(3);
        llist.addFirst(0);
        llist.addLast(142);
        llist.addFirst(-97);
        llist.deleateLast();
        llist.deleteFirst();
        System.out.println(llist);
        llist.deleteFirst();
        llist.deleateLast();
        llist.deleteFirst();
        llist.deleateLast();
        System.out.println(llist);
    }
}

LinkedList.java

//package edu.cscc;

public class LinkedList <T>{
    private Node head;

    public LinkedList() {
        head = null;
    }

    public void addFirst(T content) {
        Node ptr = head;
        head = new Node(content,ptr);
    }

    public void addLast(T content) {
        Node last = new Node(content,null);
        if (head == null) {
            head = last;
        } else {
            Node ptr = head;
            while(ptr.getNext() != null) {
                ptr = ptr.getNext();
            }
            ptr.setNext(last);
        }
    }

    public boolean deleteFirst() {
        if (head == null) {
            return false;
        } else {
            head = head.getNext();
            return true;
        }
    }

    public boolean deleateLast() {
        if (head == null) {
            return false;
        }
        else if (head.getNext() == null) {
            head = null;
            return true;
        } else {
            Node ptr = head;
            while (ptr.getNext().getNext() != null) {
                ptr = ptr.getNext();
            }
            ptr.setNext(null);
            return true;
        }
    }

    public Node getHead() {
        return head;
    }

    public String toString() {
        String str;
        if (head == null) {
            str = "<empty>";
        } else {
            Node ptr = head;
            str = "("+ptr.getContent().toString()+")";
            while(ptr.getNext() != null) {
                str = str + "->";
                ptr = ptr.getNext();
                str = str + "(" + ptr.getContent().toString() + ")";
            }
        }
        return str;
    }
}

Node.java

public class Node <T>{
    private T content;
    private Node next;

    public Node(T content, Node next) {
        this.content = content;
        this.next = next;
    }

    public T getContent() {
        return content;
    }

    public void setContent(T content) {
        this.content = content;
    }

    public Node getNext() {
        return next;
    }

    public void setNext(Node next) {
        this.next = next;
    }
}