Merge pull request #3 from RianGallagher/master

Added an array implementation of a stack

data_structures/Stacks.java

@@ -0,0 +1,57 @@
+/*
+ *A stack is exactly what it sounds like. An element gets added to top of the stack and only the element on the top may be removed.
+ *This is an example of an array implementation of a Stack. So an element can only be added/removed from the end of the array.
+ *In theory stacks have no fixed size, but with an array implementation it does.
+*/
+class Stack{
+	private int maxSize;
+	private int[] stackArray;
+	private int top;
+
+	public Stack(int size){ //Constructor
+		maxSize = size;
+		stackArray = new int[maxSize];
+		top = -1;
+	}
+
+	public void push(int value){ //Adds an element to the top of the stack
+		top++;
+		stackArray[top] = value;
+	}
+
+	public int pop(){ //Removes the top element of the stack and returns the value you've removed
+		return stackArray[top--];
+	}
+
+	public int peek(){ //Returns the element at the top of the stack
+		return stackArray[top];
+	}
+
+	public boolean isEmpty(){ //Returns true if the stack is empty
+		return(top == -1);
+	}
+
+	public boolean isFull(){ //Returns true if the stack is full
+		return(top+1 == maxSize);
+	}
+	public void makeEmpty(){ //Doesn't delete elements in the array but if you call
+		top = -1;			 //push method after calling makeEmpty it will overwrite previous values
+	}
+}
+//Example
+public class Stacks{
+	public static void main(String args[]){
+		Stack myStack = new Stack(4); //Declare a stack of maximum size 4
+		//Populate the stack
+		myStack.push(5);
+		myStack.push(8);
+		myStack.push(2);
+		myStack.push(9);
+
+		System.out.println(myStack.isEmpty()); //will print false
+		System.out.println(myStack.isFull()); //will print true
+		System.out.println(myStack.peek()); //will print 9
+		System.out.println(myStack.pop()); //will print 9
+		System.out.println(myStack.peek()); // will print 2
+	}
+}