Stack 7 January 2019 OSU CSE 1 Stack The Stack component family - - PowerPoint PPT Presentation

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Stack 7 January 2019 OSU CSE 1 Stack The Stack component family allows you to manipulate strings of entries of any (arbitrary) type in LIFO (last-in-first-out) order A kind of dual to Queue Remember, "first" and

SLIDE 1

Stack

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SLIDE 2

Stack

The Stack component family allows you

to manipulate strings of entries of any (arbitrary) type in LIFO (last-in-first-out)

rder

– A kind of “dual” to Queue – Remember, "first" and "last" here refer to the temporal order in which entries are put into the string and taken out of it, not about the

rder in the string when it is written down

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SLIDE 3

Interfaces and Classes

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Stack Stack1L Stack2 implements implements StackKernel extends Standard extends

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Interfaces and Classes

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Stack Stack1L Stack2 implements implements StackKernel extends Standard extends Standard has contracts for three methods: clear newInstance transferFrom

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Interfaces and Classes

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Stack Stack1L Stack2 implements implements StackKernel extends Standard extends StackKernel has contracts for three methods: push pop length

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Interfaces and Classes

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Stack Stack1L Stack2 implements implements StackKernel extends Standard extends Stack has a contract for three

ther methods:

top replaceTop flip

SLIDE 7

Mathematical Model

The value of a Stack variable is modeled

as a string of entries of type T

Formally:

type Stack is modeled by string of T

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No-argument Constructor

Ensures:

this = < >

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SLIDE 9

Example

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Code State

Stack<Integer> si = new Stack1L<>();

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Example

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Code State

Stack<Integer> si = new Stack1L<>(); si = < >

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push

void push(T x)

Adds x at the top (left end) of this.
Aliases: reference x
Updates: this
Ensures:

this = <x> * #this

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Example

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Code State

si = < 3, 70 > k = 49 si.push(k);

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Example

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Code State

si = < 3, 70 > k = 49 si.push(k); si = < 49, 3, 70 > k = 49

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Example

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Code State

si = < 3, 70 > k = 49 si.push(k); si = < 49, 3, 70 > k = 49 Note the alias created here, which you cannot see in the tracing table; you should be able to draw the appropriate diagram showing it.

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pop

T pop()

Removes and returns the entry at the top

(left end) of this.

Updates: this
Requires:

this /= < >

Ensures:

#this = <pop> * this

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Example

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Code State

si = < 49, 3, 70 > z = –584 z = si.pop();

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Example

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Code State

si = < 49, 3, 70 > z = –584 z = si.pop(); si = < 3, 70 > z = 49

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length

int length()

Reports the length of this.
Ensures:

length = |this|

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top

T top()

Returns the entry at the the top (left end)
f this.
Aliases: reference returned by top
Requires:

this /= < >

Ensures:

<top> is prefix of this

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Example

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Code State

si = < 49, 3, 70 > k = –58 k = si.top();

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Example

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Code State

si = < 49, 3, 70 > k = –58 k = si.top(); si = < 49, 3, 70 > k = 49

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Example

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Code State

si = < 49, 3, 70 > k = –58 k = si.top(); si = < 49, 3, 70 > k = 49 Note the alias created here, which you cannot see in the tracing table; you should be able to draw the appropriate diagram showing it.

SLIDE 23

replaceTop

T replaceTop(T x)

Replaces the top of this with x, and returns the old top.
Aliases: reference x
Updates: this
Requires:

this /= < >

Ensures:

<replaceTop> is prefix of #this and this = <x> * #this[1, |#this|)

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SLIDE 24

Example

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Code State

si = < 49, 70 > k = –58 j = 16

k = si.replaceTop(j);

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Example

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Code State

si = < 49, 70 > k = –58 j = 16

k = si.replaceTop(j);

si = < 16, 70 > k = 49 j = 16

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Example

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Code State

si = < 49, 70 > k = –58 j = 16

k = si.replaceTop(j);

si = < 16, 70 > k = 49 j = 16 Note the alias created here, which you cannot see in the tracing table; you should be able to draw the appropriate diagram showing it.

SLIDE 27

Another Example

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Code State

si = < 49, 70 > j = 16

j = si.replaceTop(j);

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Another Example

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Code State

si = < 49, 70 > j = 16

j = si.replaceTop(j);

si = < 16, 70 > j = 49

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Another Example

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Code State

si = < 49, 70 > j = 16

j = si.replaceTop(j);

si = < 16, 70 > j = 49 This use of the method avoids creating an alias: it swaps j with the entry previously at the top.

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flip

void flip()

Reverses (“flips”) this.
Updates: this
Ensures:

this = rev(#this)

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Example

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Code State

s1 = < 18, 6, 74 > s1.flip();

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Example

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Code State

s1 = < 18, 6, 74 > s1.flip(); s1 = < 74, 6, 18 >

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Resources

OSU CSE Components API: Stack

– http://cse.osu.edu/software/common/doc/

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