Added Queues and Priority Queues

Data_Structures/PriorityQueues.java

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+/*
+ * A priority queue adds elements into positions based on their priority.
+ * So the most important elements are placed at the front/on the top.
+ * In this example I give numbers that are bigger, a higher priority.
+ * Queues in theory have no fixed size but when using an array implementation it does.
+ */
+class PriorityQueue{
+	private int maxSize;
+	private int[] queueArray;
+	private int nItems;
+
+	public PriorityQueue(int size){ //Constructor
+		maxSize = size;
+		queueArray = new int[size];
+		nItems = 0;
+	}
+
+	public void insert(int value){ //Inserts an element in it's appropriate place
+		if(nItems == 0){
+			queueArray[0] = value;
+		}
+		else{
+			int j = nItems;
+			while(j > 0 && queueArray[j-1] > value){
+				queueArray[j] = queueArray[j-1];
+				j--;
+			}
+			queueArray[j] = value;
+		}
+		nItems++;
+	}
+
+	public int remove(){ //Remove the element from the front of the queue
+		return queueArray[--nItems];
+	}
+
+	public int peek(){ //Checks what's at the front of the queue
+		return queueArray[nItems-1];
+	}
+
+	public boolean isEmpty(){ //Returns true is the queue is empty
+		return(nItems == 0);
+	}
+
+	public boolean isFull(){ //Returns true is the queue is full
+		return(nItems == maxSize);
+	}
+
+	public int getSize(){ //Returns the number of elements in the queue
+		return nItems;
+	}
+}
+//Example
+public class PriorityQueues{
+	public static void main(String args[]){
+		PriorityQueue myQueue = new PriorityQueue(4);
+		myQueue.insert(10);
+		myQueue.insert(2);
+		myQueue.insert(5);
+		myQueue.insert(3);
+		//[2, 3, 5, 10] Here higher numbers have higher priority, so they are on the top
+
+		for(int i = 3; i>=0; i--)
+			System.out.print(myQueue.remove() + " "); //will print the queue in reverse order [10, 5, 3, 2]
+
+		//As you can see, a Priority Queue can be used as a sorting algotithm
+	}
+}