PositionalListVia2Stacks

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scranton.list
Class PositionalListVia2Stacks

java.lang.Object
  scranton.list.PositionalListVia2Stacks

All Implemented Interfaces:: PositionalList

public class PositionalListVia2Stacks
extends java.lang.Object
implements PositionalList

LinkedSList implements the PositionalList interface with a pair of stacks. A positional list may be specified as an ordered pair this = (i, L) where L is an n-tuple, L = () or L = (a₀, a₁, ..., a_n-1, and -1 <= i < #(L) Initially this = (-1, ()) The first ordinate, i, is the position indicator. It is either set to -1 to indicate the current position is undefined or 0<= i < #(L), indicating the current active location. Mapping: The list specification, (i,L) maps onto the attributes in LinkedSList as follows: If L = (), then left and current are empty. else if i != -1, left contains a₀, ..., a_i-1 with a_i-1 at the top of the stack current contains a_i, ..., a_n-1 with a_i at the top of the stack

Field Summary
`protected Stack`	`current` For i>0, `current` contains a_i, ..., a_n-1 with a_i at the top of the stack
`protected Stack`	`left` For i>0, `left` contains a₀, ..., a_i-1 with a_i-1 at the top of the stack

Constructor Summary
`PositionalListVia2Stacks()` Initialize the list as a pair of empty stacks.

Method Summary
`boolean`	`atFront()` Reports whether or not current viewing position is at front of list
`boolean`	`atRear()` Reports whether or not current viewing position is at rear of list
`PositionalList`	`factory()` Returns an empty PositionalList implementation of the type used in the method's application.
`void`	`insert(java.lang.Object obj)` Insert `obj` at the current position in the list Pre: #(L) = 0 or 0 <= i Post: L' = #(L)+1 if #(L)=0 then i'=0, L' = (obj) else if i>#(L)-1 then i' = #(L')-1, L' = (L, obj) else i' = i, L' = (a₀, ..., a_i-1, obj, a_i, ..., a_n-1) Mapping: `obj` is pushed into the stack, `current`, on top of other objects in that stack
`boolean`	`isEmpty()` Reports whether or not the list is empty (i.e., contains no items).
`void`	`next()` Moves current viewing position one object towards the rear, if possible.
`void`	`previous()` Moves current viewing position one place towards the front, if possible.
`java.lang.Object`	`remove()` Removes the current item from the list
`void`	`replace(java.lang.Object obj)` Replaces item at current position in the list with obj.
`void`	`toFront()` Moves current viewing position to front of list Pre: none Post: L'==(), R'==(L, R)
`void`	`toRear()` Moves current viewing position to rear of list Pre: none Post: L'==(L, R), R'==()
`java.lang.String`	`toString()` Return a string representation of a positonal list.
`java.lang.Object`	`view()` Returns a reference to the current item in list.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

left

protected Stack left

For i>0, left contains a₀, ..., a_i-1 with a_i-1 at the top of the stack

current

protected Stack current

For i>0, current contains a_i, ..., a_n-1 with a_i at the top of the stack

Constructor Detail

PositionalListVia2Stacks

public PositionalListVia2Stacks()

Initialize the list as a pair of empty stacks.

Method Detail

insert

public void insert(java.lang.Object obj)

Insert obj at the current position in the list Pre: #(L) = 0 or 0 <= i Post: L' = #(L)+1 if #(L)=0 then i'=0, L' = (obj) else if i>#(L)-1 then i' = #(L')-1, L' = (L, obj) else i' = i, L' = (a₀, ..., a_i-1, obj, a_i, ..., a_n-1) Mapping: obj is pushed into the stack, current, on top of other objects in that stack

Specified by:: insert in interface PositionalList

Parameters:: obj - New item inserted at the current position.