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118 lines (93 loc) · 3.31 KB
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/*
*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
}
}
/* This is ArrayList Implementation of stack , Where size is not
a problem we can extend the stack as much as we want*/
class Stack2{
ArrayList<Integer> stackList;
Stack2(){ //constructor
stackList=new ArrayList<>();
}
void push(int value){ //adds value to the end of list which is the top for stack
stackList.add(value);
}
int pop(){ //pops last element of list which is indeed the top for Stack
if(!isEmpty()){ // checks for an empty Stack
int popValue=stackList.get(stackList.size()-1);
stackList.remove(stackList.size()-1); //removes the poped element from the list
return popValue;
}
else{
System.out.print("The stack is already empty ");
return -1;
}
}
boolean isEmpty(){ //checks for empty Stack
if(stackList.isEmpty())
return true;
else return false;
}
int peek(){ //top element of stack
return stackList.get(stackList.size()-1);
}
}
//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("*********************Stack Array Implementation*********************");
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
Stack2 myStack2 = new Stack2(); //Declare a stack of maximum size 4
//Populate the stack
myStack2.push(5);
myStack2.push(8);
myStack2.push(2);
myStack2.push(9);
System.out.println("*********************Stack List Implementation*********************");
System.out.println(myStack2.isEmpty()); //will print false
System.out.println(myStack2.peek()); //will print 9
System.out.println(myStack2.pop()); //will print 9
System.out.println(myStack2.peek()); // will print 2
System.out.println(myStack2.pop()); //will print 2
}
}