THE PACKAGE JAVA.UTIL

java.util.Stack

21.12

21.12 The Class

java.util.Stack

. . . and from the stack a thin blue wreath of smoke

Curled through the air across the ripening oats . . .

 Oscar Wilde,

Charmides

 (1881)

The class

Stack

 extends

Vector

 with five operations that allow a vector to be

treated as a stack. The usual

push

 and

pop

 operations are provided, as well as a

method to

peek

 at the top item on the stack, a method to test for whether the stack

is

empty

, and a method to

search

 the stack for an item and discover how far it is

from the top.

public class Stack extends Vector {

public Object push(Object item);

public Object pop() throws EmptyStackException;

public Object peek() throws EmptyStackException;

public boolean empty();

public int search(Object o);

}

When a stack is first created, it contains no items.

21.12.1

public Object push(Object item)

The

item

 is pushed onto the top of this stack. This has exactly the same effect as:

addElement(item)

See method

addElement

 of

Vector

 ( 21.11.13).

21.12.2

public Object pop() throws EmptyStackException

If the stack is empty, an

EmptyStackException

 is thrown. Otherwise, the top 

most item (last item of the

Vector

) is removed and returned.

21.12.3

public Object peek() throws EmptyStackException

If the stack is empty, an

EmptyStackException

 is thrown. Otherwise, the top 

most item (last item of the

Vector

) is returned but not removed.

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