this.queue.add(0, element);

Week 7: Enum, Generic Type, Streams, write to file, class diagram/05. Generic Queue Class

@@ -0,0 +1,128 @@
+In the tutorial, a generic class Stack was introduced.
+
+Queue is a data structure similar to a stack. 
+The difference is that while in a stack, elements are added and removed from the same end, => LIFO
+in a queue, 'elements are added to the end but removed from the beginning' (just like how a queue works in real life). => FIFO
+
+
+Write a generic class Queue<T> with the following properties:
+A constructor that does not take any parameters.
+A method void add(T element) that adds an element to the front of the queue. => counterintuitive; add to the front
+A method T remove(), which removes and returns the last element of the queue. => counterintuitive; but remove from the back
+A method boolean hasElements(), which returns true if there is at least one element in the queue.
+
+
+
+
+import java.util.Random;
+import java.util.ArrayList;
+
+public class Test {
+    public static void main(String[] args) {
+        final Random r = new Random();
+        
+        System.out.println("Testing the Queue class...");
+
+        System.out.println("Testing with integer type...");
+        Queue<Integer> queue = new Queue<>();
+        int[] numbers = {2, 4, 6, 3, 5};
+
+        for (int number : numbers) {
+            System.out.println("Adding element " + number);
+            queue.add(number);
+        }
+
+        System.out.println("Removing elements until hasElements == false");
+        while (queue.hasElements()) {
+            System.out.println(queue.remove());
+        }
+        System.out.println("");
+
+        System.out.println("Testing with string type...");
+        Queue<String> queue2 = new Queue<>();
+        String[] elements = {"rabbit", "fox", "bear", "elk"};
+
+        for (String element : elements) {
+            System.out.println("Adding element " + element);
+            queue2.add(element);
+        }
+
+        System.out.println("Removing elements until hasElements == false");
+        while (queue2.hasElements()) {
+            System.out.println(queue2.remove());
+        }
+        
+    }
+}
+
+
+
+//ADD
+class Queue<T> {
+    // attributes
+    private ArrayList<T> queue;
+
+    // constructor with no params
+    public Queue(){
+        this.queue = new ArrayList<>();
+    }
+
+    // normal ArrayList
+    // https://stackoverflow.com/questions/12949690/java-arraylist-how-to-add-elements-at-the-beginning
+    // do not use LinkedList
+    // LinkedList example from Oracle
+    // https://docs.oracle.com/javase/7/docs/api/java/util/Deque.html#addFirst(E)
+    // add element to the front
+    public void add(T element) {
+        // for LinkedList
+        // this.queue.addFirst(element);
+        // for ArrayList
+        this.queue.add(0, element); 
+    }
+
+    // remove and return last element
+    public T remove() {
+        return this.queue.remove(this.queue.size() - 1);
+    }
+
+    public boolean hasElements() {
+        return this.queue.size() > 0;
+    }
+}
+
+
+
+
+
+Testing the Queue class...
+Testing with integer type...
+Adding element 2
+Adding element 4
+Adding element 6
+Adding element 3
+Adding element 5
+Removing elements until hasElements == false
+2
+4
+6
+3
+5
+
+
+
+Testing with string type...
+Adding element rabbit
+Adding element fox
+Adding element bear
+Adding element elk
+Removing elements until hasElements == false
+rabbit
+fox
+bear
+elk
+
+
+
+
+
+