understanding recursive classes

UNDERSTANDING RECURSIVE CLASSES

CMSC 150

2

StringList: A Recursive Class

public class StringList

{

// instance variables

private boolean isEmpty;

private String thisString;

private StringList restOfStringList;

// constructors

public StringList() { … }

public StringList(String newString, StringList aList) { … }

public String toString() { … }

public String getLineStartingWith(String prefix) { … }

}

3

StringList: A Recursive Class

public class StringList

{

// instance variables

private boolean isEmpty;

private String thisString;

private StringList restOfStringList;

// constructors

public StringList() { ... }

public StringList(String newString, StringList aList) {...}

public String toString() {...}

public String getLineStartingWith(String prefix) {...}

}

Data

4

StringList: A Recursive Class

public class StringList

{

// instance variables

private boolean isEmpty;

private String thisString;

private StringList restOfStringList;

// constructors

public StringList() {...}

public StringList(String newString, StringList aList) {...}

public String toString() {...}

public String getLineStartingWith(String prefix) {...}

}

Methods

5

StringList: A Recursive Class

public class StringList

{

// instance variables

private boolean isEmpty;

private String thisString;

private StringList restOfStringList;

// constructors

public StringList() { … }

public StringList(String newString, StringList aList) { … }

public String toString() { … }

public String getLineStartingWith(String prefix) { … }

}

6

StringList: In Action

StringList aList = new StringList();

aList true

""

toString()

getLine()

public class StringList

{

// instance variables

private boolean isEmpty;

private String thisString;

private StringList restOfStringList;

// constructors

public StringList() { ... }

public StringList(String newString, StringList aList) { ...}

public String toString() { ... }

public String getLineStartingWith(String prefix) { ... }

}

addr: 32

32

0

7

StringList: In Action

StringList aList = new StringList();

aList true

""

toString()

getLine()

Actually a reference to a String object, but for brevity…

addr: 32

32

0

public class StringList

{

// instance variables

private boolean isEmpty;

private String thisString;

private StringList restOfStringList;

// constructors

public StringList() { ... }

public StringList(String newString, StringList aList) { ... }

public String toString() { ... }

public String getLineStartingWith(String prefix) { ...}

}

8

StringList: In Action

StringList aList = new StringList(); aList = new StringList("mandolin", aList);

aList true

""

toString()

getLine()

addr: 32

32

0

9

StringList: In Action

StringList aList = new StringList(); aList = new StringList("mandolin", aList);

aList true

""

toString()

getLine()

toString()

getLine()

false

addr: 32

32

addr: 48

0

10

StringList: In Action

StringList aList = new StringList(); aList = new StringList("mandolin", aList);

aList true

""

toString()

getLine()

toString()

getLine()

"mandolin"

false

addr: 32

32

0

addr: 48

11

StringList: In Action

StringList aList = new StringList(); aList = new StringList("mandolin", aList);

aList true

""

toString()

getLine()

toString()

getLine()

"mandolin"

false

addr: 32

32

0

addr: 48

12

StringList: In Action

StringList aList = new StringList(); aList = new StringList("mandolin", aList);

aList true

""

toString()

getLine()

toString()

getLine()

"mandolin"

false

addr: 32

32

0

addr: 48

32

13

StringList: In Action

StringList aList = new StringList(); aList = new StringList("mandolin", aList);

aList true

""

toString()

getLine()

toString()

getLine()

"mandolin"

false

addr: 32

32

0

addr: 48

32

14

StringList: In Action

StringList aList = new StringList(); aList = new StringList("mandolin", aList);

aList true

""

toString()

getLine()

toString()

getLine()

"mandolin"

false

addr: 32

32

0

addr: 48

32

15

StringList: In Action

StringList aList = new StringList(); aList = new StringList("mandolin", aList);

aList true

""

toString()

getLine()

toString()

getLine()

"mandolin"

false

addr: 32

32

0

addr: 48

32

16

StringList: In Action

StringList aList = new StringList(); aList = new StringList("mandolin", aList);

aList true

""

toString()

getLine()

toString()

getLine()

"mandolin"

false

addr: 32

48

0

addr: 48

32

17

StringList: In Action

StringList aList = new StringList(); aList = new StringList("mandolin", aList);

aList true

""

toString()

getLine()

toString()

getLine()

"mandolin"

false

addr: 32

48

0

addr: 48

32

18

StringList: In Action

StringList aList = new StringList(); aList = new StringList("mandolin", aList); aList = new StringList("Lilly", aList);

aList true

""

toString()

getLine()

toString()

getLine()

"mandolin"

false

addr: 32

48

0

addr: 48

32

19

StringList: In Action

StringList aList = new StringList(); aList = new StringList("mandolin", aList); aList = new StringList("Lilly", aList);

aList true

""

toString()

getLine()

toString()

getLine()

"mandolin"

false

addr: 32

48

0

addr: 48

32

toString()

getLine()

false

addr: 77

"Lilly"

48

20

StringList: In Action

StringList aList = new StringList(); aList = new StringList("mandolin", aList); aList = new StringList("Lilly", aList);

aList true

""

toString()

getLine()

toString()

getLine()

"mandolin"

false

addr: 32

48

0

addr: 48

32

toString()

getLine()

false

addr: 77

"Lilly"

48

21

StringList: In Action

StringList aList = new StringList(); aList = new StringList("mandolin", aList); aList = new StringList("Lilly", aList);

aList true

""

toString()

getLine()

toString()

getLine()

"mandolin"

false

addr: 32

77

0

addr: 48

32

toString()

getLine()

false

addr: 77

"Lilly"

48

22

HistoryList: A Recursive Class

public class HistoryList

{

// instance variables

private boolean isEmpty;

private String firstWebSite;

private HistoryList restOfWebSites;

// constructors

public HistoryList() { ... }

public HistoryList(String newSite, HistoryList aList) { ... }

public boolean contains(String site) { ... }

public String toString() { ... }

public HistoryList getMatches(String prefix) { ... }

public boolean isEmpty() { ... }

}

23

HistoryList: In Action

HistoryList aList = new HistoryList(); aList = new HistoryList("cnn.com", aList); aList = new HistoryList("mlb.com", aList);

aList true

""

contains()toString()getMatches()isEmpty()

"cnn.com"

false

addr: 42

87

0

addr: 58

42

false

addr: 87

"mlb.com"

58

contains()toString()getMatches()isEmpty()

contains()toString()getMatches()isEmpty()

24

HistoryList: contains() method

public boolean contains(String site)

{

if (empty)

{

return false;

}

else if (firstWebSite.equals(site))

{

return true;

}

return restOfWebSites.contains(site);

}

25

HistoryList: contains()

boolean inList = aList.contains("cnn.com");

aList true

""

contains()toString()getMatches()isEmpty()

"cnn.com"

false

addr: 42

87

0

addr: 58

42

false

addr: 87

"mlb.com"

58

contains()toString()getMatches()isEmpty()

contains()toString()getMatches()isEmpty()

26

HistoryList: contains()

boolean inList = aList.contains("cnn.com");

aList true

""

contains()toString()getMatches()isEmpty()

"cnn.com"

false

addr: 42

87

0

addr: 58

42

false

addr: 87

"mlb.com"

58

contains()toString()getMatches()isEmpty()

contains()toString()getMatches()isEmpty()

27

HistoryList: contains()

boolean inList = aList.contains("cnn.com");

aList true

""

contains()toString()getMatches()isEmpty()

"cnn.com"

false

addr: 42

87

0

addr: 58

42

false

addr: 87

"mlb.com"

58

contains()toString()getMatches()isEmpty()

contains()toString()getMatches()isEmpty()

28

HistoryList: contains()

boolean inList = aList.contains("cnn.com");

aList true

""

contains()toString()getMatches()isEmpty()

"cnn.com"

false

addr: 42

87

0

addr: 58

42

false

addr: 87

"mlb.com"

58

contains()toString()getMatches()isEmpty()

contains()toString()getMatches()isEmpty()

29

HistoryList: contains()

boolean inList = aList.contains("cnn.com");

aList true

""

contains()toString()getMatches()isEmpty()

"cnn.com"

false

addr: 42

87

0

addr: 58

42

false

addr: 87

"mlb.com"

58

contains()toString()getMatches()isEmpty()

contains()toString()getMatches()isEmpty()

30

true

""

contains()toString()getMatches()isEmpty()

"cnn.com"

false

addr: 42

87

0

addr: 58

42

false

addr: 87

"mlb.com"

58

contains()toString()getMatches()isEmpty()

if (empty){

return false;

} else if (firstWebSite.equals(site)) {

return true;

}

return restOfWebSites.contains(site);

contains()toString()getMatches()isEmpty()

aList

31

true

""

contains()toString()getMatches()isEmpty()

"cnn.com"

false

addr: 42

87

0

addr: 58

42

false

addr: 87

"mlb.com"

58

contains()toString()getMatches()isEmpty()

contains()toString()getMatches()isEmpty()

aList

if (empty){

return false;

} else if (firstWebSite.equals(site)) {

return true;

}

return restOfWebSites.contains(site);

32

true

""

contains()toString()getMatches()isEmpty()

"cnn.com"

false

addr: 42

87

0

addr: 58

42

false

addr: 87

"mlb.com"

58

contains()toString()getMatches()isEmpty()

contains()toString()getMatches()isEmpty()

aList

if (empty){

return false;

} else if (firstWebSite.equals(site)) {

return true;

}

return restOfWebSites.contains(site);

33

true

""

contains()toString()getMatches()isEmpty()

"cnn.com"

false

addr: 42

87

0

addr: 58

42

false

addr: 87

"mlb.com"

58

contains()toString()getMatches()isEmpty()

contains()toString()getMatches()isEmpty()

aList

if (empty){

return false;

} else if (firstWebSite.equals(site)) {

return true;

}

return restOfWebSites.contains(site);

34

true

""

contains()toString()getMatches()isEmpty()

"cnn.com"

false

addr: 42

87

0

addr: 58

42

false

addr: 87

"mlb.com"

58

contains()toString()getMatches()isEmpty()

contains()toString()getMatches()isEmpty()

aList

if (empty){

return false;

} else if (firstWebSite.equals(site)) {

return true;

}

return restOfWebSites.contains(site);

35

true

""

contains()toString()getMatches()isEmpty()

"cnn.com"

false

addr: 42

87

0

addr: 58

42

false

addr: 87

"mlb.com"

58

contains()toString()getMatches()isEmpty()

contains()toString()getMatches()isEmpty()

aList

if (empty){

return false;

} else if (firstWebSite.equals(site)) {

return true;

}

return restOfWebSites.contains(site);

36

true

""

contains()toString()getMatches()isEmpty()

"cnn.com"

false

addr: 42

87

0

addr: 58

42

false

addr: 87

"mlb.com"

58

contains()toString()getMatches()isEmpty()

contains()toString()getMatches()isEmpty()

aList

if (empty){

return false;

} else if (firstWebSite.equals(site)) {

return true;

}

return restOfWebSites.contains(site);

37

true

""

contains()toString()getMatches()isEmpty()

"cnn.com"

false

addr: 42

87

0

addr: 58

42

false

addr: 87

"mlb.com"

58

contains()toString()getMatches()isEmpty()

contains()toString()getMatches()isEmpty()

aList

if (empty){

return false;

} else if (firstWebSite.equals(site)) {

return true;

}

return restOfWebSites.contains(site);

38

true

""

contains()toString()getMatches()isEmpty()

"cnn.com"

false

addr: 42

87

0

addr: 58

42

false

addr: 87

"mlb.com"

58

contains()toString()getMatches()isEmpty()

contains()toString()getMatches()isEmpty()

aList

if (empty){

return false;

} else if (firstWebSite.equals(site)) {

return true;

}

return restOfWebSites.contains(site);

true

39

true

""

contains()toString()getMatches()isEmpty()

"cnn.com"

false

addr: 42

87

0

addr: 58

42

false

addr: 87

"mlb.com"

58

contains()toString()getMatches()isEmpty()

contains()toString()getMatches()isEmpty()

aList

if (empty){

return false;

} else if (firstWebSite.equals(site)) {

return true;

}

return restOfWebSites.contains(site);

true

true

40

true

""

contains()toString()getMatches()isEmpty()

"cnn.com"

false

addr: 42

87

0

addr: 58

42

false

addr: 87

"mlb.com"

58

contains()toString()getMatches()isEmpty()

contains()toString()getMatches()isEmpty()

aList

if (empty){

return false;

} else if (firstWebSite.equals(site)) {

return true;

}

return restOfWebSites.contains(site);

true

true

true

41

HistoryList: contains()

boolean inList = aList.contains("cnn.com");

true

""

contains()toString()getMatches()isEmpty()

"cnn.com"

false

addr: 42

87

0

addr: 58

42

false

addr: 87

"mlb.com"

58

contains()toString()getMatches()isEmpty()

contains()toString()getMatches()isEmpty()

aList

true

true

true

42

HistoryList: contains()

boolean inList = aList.contains("cnn.com");

true

""

contains()toString()getMatches()isEmpty()

"cnn.com"

false

addr: 42

87

0

addr: 58

42

false

addr: 87

"mlb.com"

58

contains()toString()getMatches()isEmpty()

contains()toString()getMatches()isEmpty()

aList

true

true

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