class Node{
private String value = null;
private Node next=null;
public Node(String value){
this.value= value;
}
public void setValue(String value){
this.value = value;
}
public String getValue(){
return this.value;
}
public void setNext(Node next){
this.next = next;
}
public Node getNext(){
return this.next;
}
}
class Queue{
private Node firstElement= null;
private Node lastElement = null;
private int length= 0;
public Queue(){
}
public String peek(){
if (this.length ==0){
System.out.println("The queue is empty, not value to peek.");
return null;
}
return this.firstElement.getValue();
}
public void enqueue(String value){
Node newElement = new Node(value);
if (firstElement == null){
firstElement = newElement;
}
if (lastElement == null){
lastElement = newElement;
} else {
lastElement.setNext(newElement);
lastElement= newElement;
}
this.length++;
}
public String dequeue(){
if (this.length == 0){
System.out.println("The queue is empty, no value can be dequeued.");
return null;
}
Node dequeuedElement = firstElement;
firstElement = firstElement.getNext();
this.length--;
return dequeuedElement.getValue();
}
public void printAll(){
if (this.length == 0){
System.out.println("The queue is empty, no values can be printed.");
return;
}
Node currentElement = firstElement;
while (currentElement != null){
System.out.println(currentElement.getValue());
currentElement = currentElement.getNext();
}
}
}
class Main {
public static void main(String[] args) {
Queue queue = new Queue();
queue.enqueue("1");
System.out.println("Peek: "+ queue.peek());
queue.enqueue("2");
queue.enqueue("3");
queue.printAll();
System.out.println("Peek: "+ queue.peek());
queue.dequeue();
System.out.println("Peek: "+ queue.peek());
queue.enqueue("4");
}
}
