Java Queue.This program result is empty.

Question

I am learning the Queue Data structure.I want to create Queue with linked list.I want to program ouput : 10 20 Program output: Queue empty -1 Queue empty -1

Where am I making mistakes?

The code is as given below:

class Node {
  int x;
  Node next;

  Node (int x){
    this.x=x;
    next=null;

}

}

public class QueQueLinked {
 static Node root=null;
 static Node latest=null;

 public static void enque(int x){
    if(root==null){
        Node root=new Node(x);
        root.x=x;
        root.next=null;
        latest=root;
    }

    else{
        latest.next=new Node(x);
        latest=latest.next;
        latest.next=null;


    }

}

public static int deque(){
    if(root==null){
        System.out.println("Queque empty");
        return -1;

    }
    int value=root.x;
    root=root.next;

    return value;
}

public static void main(String[] args) {
   enque(10);
   enque(20);

    System.out.println(deque());
    System.out.println(deque());
}

}

BlackHatSamurai · Accepted Answer · 2016-12-07 19:55:44Z

2

You are overwriting your root variable. You need to do:

public static void enque(int x){
    if(root==null){
        root=new Node(x);
        root.x=x;
        root.next=null;
        latest=root;
    }

answered Dec 7, 2016 at 19:55

BlackHatSamurai

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Comments

D. Schmidt · Accepted Answer · 2016-12-07 20:01:38Z

2

Your error is in this line:

Node root=new Node(x);

You are creating a new local variable named root that hides the the static field root. Instead you should write:

root=new Node(x);

If you have a local variable root that hides the static field root you could also access the static field by prepending it with your class name:

QueQueLinked.root = new Node(x)

In this case, however, you should rethink your variable names.

answered Dec 7, 2016 at 20:01

D. Schmidt

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