Java Stack Class
Stack is a subclass of Vector that implements a standard last-in, first-out stack.
The Stack class only defines the default constructor, which is used to create an empty stack. In addition to all the methods defined by Vector, Stack also defines some of its own methods.
Stack()
In addition to all the methods defined by Vector, it also defines some of its own methods:
| No. | Method Description |
|---|---|
| 1 | boolean empty() <br>Tests if the stack is empty. |
| 2 | Object peek() <br>Looks at the object at the top of the stack without removing it from the stack. |
| 3 | Object pop() <br>Removes the object at the top of the stack and returns that object as the value of this function. |
| 4 | Object push(Object element) <br>Pushes an item onto the top of the stack. |
| 5 | int search(Object element) <br>Returns the position of the object in the stack, with the base index as 1. |
Example
The following program demonstrates several methods supported by this collection:
import java.util.*;
public class StackDemo {
static void showpush(Stack<Integer> st, int a) {
st.push(new Integer(a));
System.out.println("push(" + a + ")");
System.out.println("stack: " + st);
}
static void showpop(Stack<Integer> st) {
System.out.print("pop -> ");
Integer a = (Integer) st.pop();
System.out.println(a);
System.out.println("stack: " + st);
}
public static void main(String args[]) {
Stack<Integer> st = new Stack<Integer>();
System.out.println("stack: " + st);
showpush(st, 42);
showpush(st, 66);
showpush(st, 99);
showpop(st);
showpop(st);
showpop(st);
try {
showpop(st);
} catch (EmptyStackException e) {
System.out.println("empty stack");
}
}
}
The above example compiles and runs with the following result:
stack: [ ]
push(42)
stack: [42]
push(66)
stack: [42, 66]
push(99)
stack: [42, 66, 99]
pop -> 99
stack: [42, 66]
pop -> 66
stack: [42]
pop -> 42
stack: [ ]
pop -> empty stack