Thread: Double-ended queue in Java

I managed to code it myself after all... here's my solution:

class Deque {



private Node front, rear;
private int counter;

public Deque() {
front = null;
rear = null;
counter = 0;
}

public void push(Object x) {
if (front==null) {
Node T = new Node(x, null, null);
rear = T;
front = T;
counter++;
} else {
Node T = new Node(x, front, null);
front.next=T;
front = T;
counter++;
}

}

public Object pop() {
if (counter==0) {
return null;
} else if (counter==1) {
counter=0;
Object x = front.data;
rear = null;
front = null;
return x;
}
else {
Object x = front.data;
front=front.prev;
rear.prev = front;
counter--;
return x;
}
}

public void inject (Object x) {
if (rear==null) {
Node T = new Node(x, null, null);
rear = T;
front = T;
counter++;
} else {
Node T = new Node(x, null, rear);
rear.prev=T;
rear = T;
counter++;
}
}

public Object eject() {
if (counter==0) {
rear=null;
front=null;
return null;
} else if (counter==1) {
counter=0;
Object x = rear.data;
rear=null;
front=null;
return x;
}
else {
Object x = rear.data;
rear=rear.next;
front.next = rear;
counter--;
return x;
}
}

class Node {

Node prev;
Node next;
Object data;

Node(Object d, Node p, Node n) {
next = n;
prev = p;
data = d;
}

}

}

I managed to code it so that all operations are done in constant time, O(1) complexity, but it should be possible implement it without the counter. I also think that there are more unnecessary things in my solution and I would like to know how you can make it more compact.

Why are you using Objects everywhere and not generics?

Originally Posted by roamer

Why are you using Objects everywhere and not generics?

I'm not familiar with the concept and this was an assignment I had to write from scratch. I'm still learning java. This was a task given at a course on data structures.