diff --git a/DataStructures/Stacks/StackArray.java b/DataStructures/Stacks/StackArray.java new file mode 100644 index 000000000..795958e8a --- /dev/null +++ b/DataStructures/Stacks/StackArray.java @@ -0,0 +1,146 @@ +/** + * This class implements a Stack using a regular array. + * + * A stack is exactly what it sounds like. An element gets added to the 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 stack have no fixed size, but with an + * array implementation it does. + * + * @author Unknown + * + */ +public class StackArray{ + + /** + * Main method + * + * @param args Command line arguments + */ + public static void main(String[] args) { + StackArray myStackArray = new StackArray(4); //Declare a stack of maximum size 4 + //Populate the stack + myStackArray.push(5); + myStackArray.push(8); + myStackArray.push(2); + myStackArray.push(9); + + System.out.println("*********************Stack Array Implementation*********************"); + System.out.println(myStackArray.isEmpty()); //will print false + System.out.println(myStackArray.isFull()); //will print true + System.out.println(myStackArray.peek()); //will print 9 + System.out.println(myStackArray.pop()); //will print 9 + System.out.println(myStackArray.peek()); // will print 2 + } + + /** The max size of the Stack */ + private int maxSize; + + /** The array representation of the Stack */ + private int[] stackArray; + + /** The top of the stack */ + private int top; + + /** + * Constructor + * + * @param size Size of the Stack + */ + public StackArray(int size){ + maxSize = size; + stackArray = new int[maxSize]; + top = -1; + } + + /** + * Adds an element to the top of the stack + * + * @param value The element added + */ + public void push(int value){ + if(!isFull()){ //Checks for a full stack + top++; + stackArray[top] = value; + }else{ + resize(maxSize*2); + push(value);// don't forget push after resizing + } + } + + /** + * Removes the top element of the stack and returns the value you've removed + * + * @return value popped off the Stack + */ + public int pop(){ + if(!isEmpty()){ //Checks for an empty stack + return stackArray[top--]; + } + + if(top < maxSize/4){ + resize(maxSize/2); + return pop();// don't forget pop after resizing + } + else{ + System.out.println("The stack is already empty"); + return -1; + } + } + + /** + * Returns the element at the top of the stack + * + * @return element at the top of the stack + */ + public int peek(){ + if(!isEmpty()){ //Checks for an empty stack + return stackArray[top]; + }else{ + System.out.println("The stack is empty, cant peek"); + return -1; + } + } + + private void resize(int newSize){ + //private int[] transferArray = new int[newSize]; we can't put modifires here ! + int[] transferArray = new int[newSize]; + + //for(int i = 0; i < stackArray.length(); i++){ the length isn't a method . + for(int i = 0; i < stackArray.length; i++){ + transferArray[i] = stackArray[i]; + stackArray = transferArray; + } + maxSize = newSize; + } + + /** + * Returns true if the stack is empty + * + * @return true if the stack is empty + */ + public boolean isEmpty(){ + return(top == -1); + } + + /** + * Returns true if the stack is full + * + * @return true if the stack is full + */ + public boolean isFull(){ + return(top+1 == maxSize); + } + + /** + * Deletes everything in the Stack + * + * Doesn't delete elements in the array + * but if you call push method after calling + * makeEmpty it will overwrite previous + * values + */ + 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 + } +} \ No newline at end of file