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

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 "last" here refer to the temporal order in which entries are put into the string and taken out of it, not about the order in the string when it is written down 7 January 2019 OSU CSE 2

Interfaces and Classes Standard extends StackKernel extends Stack implements implements Stack1L Stack2 7 January 2019 OSU CSE 3

Interfaces and Classes Standard extends Standard has contracts StackKernel for three methods: clear newInstance extends transferFrom Stack implements implements Stack1L Stack2 7 January 2019 OSU CSE 4

Interfaces and Classes Standard extends StackKernel extends StackKernel has contracts for three Stack methods: implements implements push pop Stack1L Stack2 length 7 January 2019 OSU CSE 5

Interfaces and Classes Stack Standard has a contract for three other methods: top extends replaceTop StackKernel flip extends Stack implements implements Stack1L Stack2 7 January 2019 OSU CSE 6

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 7 January 2019 OSU CSE 7

No-argument Constructor • Ensures: this = < > 7 January 2019 OSU CSE 8

Example Code State Stack<Integer> si = new Stack1L<>(); 7 January 2019 OSU CSE 9

Example Code State Stack<Integer> si = new Stack1L<>(); si = < > 7 January 2019 OSU CSE 10

push void push(T x) • Adds x at the top (left end) of this . • Aliases: reference x • Updates: this • Ensures: this = <x> * # this 7 January 2019 OSU CSE 11

Example Code State si = < 3, 70 > k = 49 si.push(k); 7 January 2019 OSU CSE 12

Example Code State si = < 3, 70 > k = 49 si.push(k); si = < 49, 3, 70 > k = 49 7 January 2019 OSU CSE 13

Example Note the alias created Code State here, which you cannot see in the tracing table; si = < 3, 70 > you should be able to k = 49 draw the appropriate diagram showing it. si.push(k); si = < 49, 3, 70 > k = 49 7 January 2019 OSU CSE 14

pop T pop() • Removes and returns the entry at the top (left end) of this . • Updates: this • Requires: this /= < > • Ensures: # this = <pop> * this 7 January 2019 OSU CSE 15

Example Code State si = < 49, 3, 70 > z = –584 z = si.pop(); 7 January 2019 OSU CSE 16

Example Code State si = < 49, 3, 70 > z = –584 z = si.pop(); si = < 3, 70 > z = 49 7 January 2019 OSU CSE 17

length int length() • Reports the length of this . • Ensures: length = | this | 7 January 2019 OSU CSE 18

top T top() • Returns the entry at the the top (left end) of this . • Aliases: reference returned by top • Requires: this /= < > • Ensures: <top> is prefix of this 7 January 2019 OSU CSE 19

Example Code State si = < 49, 3, 70 > k = –58 k = si.top(); 7 January 2019 OSU CSE 20

Example Code State si = < 49, 3, 70 > k = –58 k = si.top(); si = < 49, 3, 70 > k = 49 7 January 2019 OSU CSE 21

Example Note the alias created Code State here, which you cannot see in the tracing table; si = < 49, 3, 70 > you should be able to k = –58 draw the appropriate diagram showing it. k = si.top(); si = < 49, 3, 70 > k = 49 7 January 2019 OSU CSE 22

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 |) 7 January 2019 OSU CSE 23

Example Code State si = < 49, 70 > k = –58 j = 16 k = si.replaceTop(j); 7 January 2019 OSU CSE 24

Example Code State si = < 49, 70 > k = –58 j = 16 k = si.replaceTop(j); si = < 16, 70 > k = 49 j = 16 7 January 2019 OSU CSE 25

Example Note the alias created Code State here, which you cannot see in the tracing table; si = < 49, 70 > you should be able to k = –58 draw the appropriate j = 16 diagram showing it. k = si.replaceTop(j); si = < 16, 70 > k = 49 j = 16 7 January 2019 OSU CSE 26

Another Example Code State si = < 49, 70 > j = 16 j = si.replaceTop(j); 7 January 2019 OSU CSE 27

Another Example Code State si = < 49, 70 > j = 16 j = si.replaceTop(j); si = < 16, 70 > j = 49 7 January 2019 OSU CSE 28

Another Example This use of the method Code State avoids creating an alias: it swaps j with the entry si = < 49, 70 > previously at the top. j = 16 j = si.replaceTop(j); si = < 16, 70 > j = 49 7 January 2019 OSU CSE 29

flip void flip() • Reverses (“flips”) this . • Updates: this • Ensures: this = rev (# this ) 7 January 2019 OSU CSE 30

Example Code State s1 = < 18, 6, 74 > s1.flip(); 7 January 2019 OSU CSE 31

Example Code State s1 = < 18, 6, 74 > s1.flip(); s1 = < 74, 6, 18 > 7 January 2019 OSU CSE 32

Resources • OSU CSE Components API: Stack – http://cse.osu.edu/software/common/doc/ 7 January 2019 OSU CSE 33