Notes

public class ArrayStackPT < mytype > implements StackPT < mytype >
{

private static int DEFAULT_CAPACITY = 100; // suppose capacity is 100.

private Object stack[ ]; // The array

private int top;
//Creates a stack with the default capacity
public ArrayStackPT () {
this(DEFAULT_CAPACITY);
}
//Creates a stack with a user-specified capacity
public ArrayStackPT (int capacity) {
if (capacity < 1)
System.out.println("Capacity must > 0 ");
stack = (mytype[]) new Object[capacity];
top = -1;
}
public int size() {
return top + 1; // return the number of elements
}

public boolean isEmpty() {
return (top == -1);
}


public boolean isFull() {
return (size() == stack.length);
}
public void push(mytype x) {
if (! isFull()){

top = top + 1; // increment the counter
stack[top] = x ; //insert the item

}else{
System.out.println("Stack is full");
}
}
public mytype pop( ) {
if ( isEmpty())
throw new IllegalStateException ("Stack is empty");
mytype topItem = (mytype)stack[top];
stack[top] = null;
top = top - 1;
return topItem;
}

public mytype peek() {
if (isEmpty())
throw new IllegalStateException ("Stack is empty");
return (mytype)stack[top];
}

} // end of ArrayStackPT. java