understanding recursive classes cmsc 150: lecture 22

UNDERSTANDING RECURSIVE CLASSES

CMSC 150: Lecture 22

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) { … }

}

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

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

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) { … }

}

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

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StringList: In Action

StringList aList = new StringList();

aList true

""

toString()

getLine()

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

addr: 32

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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) { … }

}

StringList: In Action

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

aList true

""

toString()

getLine()

addr: 32

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StringList: In Action

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

aList true

""

toString()

getLine()

toString()

getLine()

false

addr: 32

32

addr: 48

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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

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

StringList: In Action

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

aList true

""

toString()

getLine()

toString()

getLine()

"mandolin"

false

addr: 32

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0

addr: 48

32

StringList: In Action

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

aList true

""

toString()

getLine()

toString()

getLine()

"mandolin"

false

addr: 32

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0

addr: 48

32

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

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

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

StringList: In Action

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

aList true

""

toString()

getLine()

toString()

getLine()

"mandolin"

false

addr: 32

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0

addr: 48

32

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

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0

addr: 48

32

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

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0

addr: 48

32

toString()

getLine()

false

addr: 77

"Lilly"

48

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

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

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() { … }

}

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()

HistoryList: contains() method

public boolean contains(String site)

{

if (empty)

{

return false;

}

else if (firstWebSite.equals(site))

{

return true;

}

return restOfWebSites.contains(site);

}

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()

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()

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()

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()

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()

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

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

""

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

""

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

""

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

""

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

""

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

""

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

""

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

""

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

""

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

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

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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