implement the Stack ADT,Queue ADT using a singly linked list

stack ADT
import java.io.*;
class Stack
{
Stack top,next,prev;
int data;
Stack()
{
data=0;
next=prev=null;
}
Stack(int d)
{
data=d;
next=prev=null;
}
void push(int n)
{
Stack nn;
nn=new Stack(n);
if(top==null)
top=nn;
else
{
nn.next=top;
top.prev=nn;
top=nn;
}
}
int pop()
{
int k=top.data;
if(top.next==null){
top=null;
return k;}
else{
top=top.next;
top.prev=null;
return k;
}
}
boolean isEmpty()
{
if(top==null)
return true;
else
return false;
}
void display()
{
Stack ptr;
for(ptr=top;ptr!=null;ptr=ptr.next)
System.out.print(ptr.data+" ");
}
public static void main(String args[ ])throws Exception
{
int x;
int ch;
BufferedReader b=new BufferedReader(new InputStreamReader(System.in));
Stack a=new Stack();
do{
System.out.println("enter 1 for pushing");
System.out.println("enter 2 for poping");
System.out.println("enter 3 for isEmpty");
System.out.println("enter 4 for display");
System.out.println("Enter 0 for exit");
System.out.println("enter ur choice ");
ch=Integer.parseInt(b.readLine());
switch(ch)
{
case 1:System.out.println("enter element to insert");
int e=Integer.parseInt(b.readLine());
a.push(e);
break;
case 2:if(!a.isEmpty())
{
int p=a.pop();
System.out.println("deleted element is "+p);
}
else
{
System.out.println("stack is empty");
}
break;
case 3:System.out.println(a.isEmpty());
break;
case 4:if(!a.isEmpty())
{
a.display();
}
else
{
System.out.println("list is empty");
}
}
}while(ch!=0);
}
}
OUTPUT:

b. queue ADT
import java.io.*;
class Qlnk
{
Qlnk front,rear,next;
int data;
Qlnk()
{
data=0;
next=null;
}
Qlnk(int d)
{
data=d;
next=null;
}
Qlnk getFront()
{
return front;
}
Qlnk getRear()
{
return rear;
}
void insertelm(int item)
{
Qlnk nn;
nn=new Qlnk(item);
if(isEmpty())
{
front=rear=nn;
}
else
{
rear.next=nn;
rear=nn;
}
}
int delelm()
{
if(isEmpty())
{
System.out.println("deletion failed");
return -1;
}
else
{
int k=front.data;
if(front!=rear)
front=front.next;
else
rear=front=null;
return k;
}
}
boolean isEmpty()
{
if(rear==null)
return true;
else
return false;
}
int size()
{
Qlnk ptr;
int cnt=0;
for(ptr=front;ptr!=null;ptr=ptr.next)
cnt++;
return cnt;
}
void display()
{
Qlnk ptr;
if(!isEmpty())
{
for(ptr=front;ptr!=null;ptr=ptr.next)
System.out.print(ptr.data+" ");
}
else
System.out.println("q is empty");
}
public static void main(String arr[])throws Exception
{
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
Qlnk m=new Qlnk();
int ch;
do
{
System.out.println("enter 1 for insert");
System.out.println("enter 2 for deletion");
System.out.println("enter 3 for getFront");
System.out.println("enter 4 for getRear");
System.out.println("enter 5 for size");
System.out.println("enter 6 for display");
System.out.println("enter 0 for exit");
System.out.println("enter ur choice");
ch=Integer.parseInt(br.readLine());
switch(ch)
{
case 1:System.out.println("enter ele to insert");
int item=Integer.parseInt(br.readLine());
m.insertelm(item);break;
case 2:int k=m.delelm();
System.out.println("deleted ele is "+k);break;
case 3:System.out.println("front index is"+(m.getFront()).data);break;
case 4:System.out.println("rear index is"+(m.getRear()).data);break;
case 5:System.out.println("size is"+m.size());break;
case 6:m.display();break;
}
}while(ch!=0);
}
}