113 lines
2.6 KiB
Java
113 lines
2.6 KiB
Java
package DataStructures.Stacks;
|
|
|
|
import java.util.ArrayList;
|
|
import java.util.EmptyStackException;
|
|
|
|
/**
|
|
* This class implements a Stack using an ArrayList.
|
|
* <p>
|
|
* 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.
|
|
* <p>
|
|
* This is an ArrayList Implementation of a stack, where size is not
|
|
* a problem we can extend the stack as much as we want.
|
|
*/
|
|
public class StackArrayList {
|
|
|
|
/**
|
|
* Driver Code
|
|
*/
|
|
public static void main(String[] args) {
|
|
StackArrayList stack = new StackArrayList();
|
|
assert stack.isEmpty();
|
|
|
|
for (int i = 1; i <= 5; ++i) {
|
|
stack.push(i);
|
|
assert stack.size() == i;
|
|
}
|
|
|
|
assert stack.size() == 5;
|
|
assert stack.peek() == 5 && stack.pop() == 5 && stack.peek() == 4;
|
|
|
|
/* pop elements at the top of this stack one by one */
|
|
while (!stack.isEmpty()) {
|
|
stack.pop();
|
|
}
|
|
assert stack.isEmpty();
|
|
|
|
try {
|
|
stack.pop();
|
|
assert false; /* this should not happen */
|
|
} catch (EmptyStackException e) {
|
|
assert true; /* this should happen */
|
|
}
|
|
|
|
}
|
|
|
|
/**
|
|
* ArrayList representation of the stack
|
|
*/
|
|
private ArrayList<Integer> stack;
|
|
|
|
/**
|
|
* Constructor
|
|
*/
|
|
public StackArrayList() {
|
|
stack = new ArrayList<>();
|
|
}
|
|
|
|
/**
|
|
* Adds value to the end of list which
|
|
* is the top for stack
|
|
*
|
|
* @param value value to be added
|
|
*/
|
|
public void push(int value) {
|
|
stack.add(value);
|
|
}
|
|
|
|
/**
|
|
* Removes the element at the top of this stack and returns
|
|
*
|
|
* @return Element popped
|
|
* @throws EmptyStackException if the stack is empty.
|
|
*/
|
|
public int pop() {
|
|
if (isEmpty()) {
|
|
throw new EmptyStackException();
|
|
}
|
|
|
|
/* remove the element on the top of the stack */
|
|
return stack.remove(stack.size() - 1);
|
|
}
|
|
|
|
/**
|
|
* Test if the stack is empty.
|
|
*
|
|
* @return {@code true} if this stack is empty, {@code false} otherwise.
|
|
*/
|
|
public boolean isEmpty() {
|
|
return stack.isEmpty();
|
|
}
|
|
|
|
/**
|
|
* Return the element at the top of this stack without removing it from the stack.
|
|
*
|
|
* @return the element at the top of this stack.
|
|
*/
|
|
public int peek() {
|
|
if (isEmpty()) {
|
|
throw new EmptyStackException();
|
|
}
|
|
return stack.get(stack.size() - 1);
|
|
}
|
|
|
|
/**
|
|
* Return size of this stack.
|
|
*
|
|
* @return size of this stack.
|
|
*/
|
|
public int size() {
|
|
return stack.size();
|
|
}
|
|
} |