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package Implementations;

public class Queue<T> {

private QueueItem<T> first;

private QueueItem<T> last;

private int size = 0;

public void enqueue(T value){

if(first == null && last == null)

first = last = new QueueItem<>(value, null);

else {

QueueItem<T> newItem = new QueueItem<>(value, null);

last.nextItem = newItem;

last = newItem;

}

size++;

}

public T dequeue(){

if(first == null)

return null;

T out = first.value;

if(first.nextItem == null)

first = last = null;

else

first = first.nextItem;

size--;

return out;

}

public T peek(){

if(first == null)

return null;

return first.value;

}

public int getSize(){

return size;

}

@Override

public String toString() {

StringBuilder sb = new StringBuilder("[ ");

QueueItem item = first;

while (item != null){

sb.append(item.value.toString());

if(item.nextItem != null)

sb.append(", ");

item = item.nextItem;

}

sb.append(" ]");

return sb.toString();

}

}

class QueueItem<T>{

T value;

QueueItem nextItem;

QueueItem(T value, QueueItem nextItem){

this.value = value;

this.nextItem = nextItem;

}

}