Today’s topics
Java
Information Retrieval
Upcoming
Database Programs
Reading
Great Ideas, Chapter 4
CompSci 001
12.1
Information Retrieval
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Often want to use program for information storage and
retrieval
On line phone book is good example
Using “Parallel” or “Corresponding Arrays”
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Array (of Strings) for Names
Array (of Strings) for Phone Numbers
Name
Number
“J.Able”
“613-1978”
“D.Ramm”
“660-6532”
“D.Ramm”
“732-7616”
“R.Odom”
“681-6326”
“M.Salter”
“684-8111”
“W.Tars”
“613-1978”
CompSci 001
12.2
Phone Lookup Program
public class LookUp extends java.applet.Applet implements
ActionListener
{ TextField gName, gNum, mInstruct;
String Name[]={"J.Able", "D.Ramm", "D.Ramm", "R.Odom",
"M.Salter", "W.Tars"};
String Num[]= {"613-1978","660-6532","732-7616",
"681-6326","684-8111","613-1978"};
Button bByName, bByNum;
TextArea mResults;
String name, num;
int size;
public void init() {
mInstruct = new TextField(60);
mInstruct.setText(
"Enter search info; push related button");
CompSci 001
12.3
Phone Lookup Program.2
gName = new TextField(25);
gNum = new TextField(25);
bByName = new Button("ByName");
bByNum = new Button("ByNum");
mResults = new TextArea(10, 60);
bByName.addActionListener(this);
bByNum.addActionListener(this);
add(mInstruct); add(gName); add(bByName); add(gNum);
add(bByNum); add(mResults);
size = 6;
// could also use: size = Name.length;
}
public void actionPerformed(ActionEvent event) {
Object cause = event.getSource();
int k=0;
CompSci 001
12.4
Phone Lookup Program.3
if (cause == bByName) {
name = gName.getText();
while (k < size) {
if (name.equals(Name[k]))
mResults.append("Name: " + name + " shows number: "
+ Num[k] + "\n");
k = k + 1;
}
}
if (cause == bByNum) {
num = gNum.getText();
while (k < size) {
if (num.equals(Num[k]))
mResults.append("Number: " + num + " shows name: "
+ Name[k] + "\n");
k = k + 1;
}
}
}
}
CompSci 001
12.5
Shortcomings?
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Must enter exact match to one of the entries
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Typing “Ramm” gets no answers
Can’t enter partial number either
Imagine Law Enforcement Application
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Partial entries desirable
Solving the “phone list” problems solve it here too
How about license plate with “holes”
o E.g., A_C-12_45
(where underscore denotes possible missing data)
Require regular expression search
This goes beyond what we can easily do
CompSci 001
12.6
Search Using a Single Array
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Can solve most of the previous problems easily
Put all relevant info about one phone in one string
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Need additional String method
indexOf method (shown briefly earlier)
int indexOf(String key)
 Searches for first occurrence of key with object string
 Returns starting position of key:
must be greater than or equal to 0
(>=0)
 What if it doesn’t find the string (key) sought?
 Needs to return something that can’t be mistaken for location of
string
 ?

Resulting program is much more flexible
CompSci 001
12.7
Search Program
public class Search extends java.applet.Applet implements
ActionListener
{ TextField gKey, mInstruct;
String Info[]={"J.Able, 613-1978", "D.Ramm, 660-6532",
"D.Ramm, 732-7616", "R.Odom, 681-6326",
"M.Salter, 684-8111", "W.Tars, 613-1978"};
Button bSearch;
TextArea mResults;
String key;
int size = 6; // or Info.length
public void init() {
mInstruct = new TextField(60);
mInstruct.setText(
"Enter search info; push button");
gKey = new TextField(35);
bSearch = new Button("Search");
CompSci 001
12.8
Search Program.2
mResults = new TextArea(10, 60);
bSearch.addActionListener(this);
add(mInstruct); add(gKey); add(bSearch); add(mResults);
}
public void actionPerformed(ActionEvent event) {
Object cause = event.getSource();
int k=0;
if (cause == bSearch) {
key = gKey.getText();
while (k < size) {
if (Info[k].indexOf(key) >= 0)
mResults.append(Info[k]+"\n");
k = k + 1;
}
}
}
}
CompSci 001
12.9
Database
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Extend ideas used in phone program
Can have many “parallel” arrays
Design Used Car Database
Make
Style
Color
Owner
Year
“Mercedes”
“4 door”
“white”
“M.Ramm”
1987
“Mercedes”
“4 door”
“ivory”
“D.Ramm”
1987
“Ford”
“truck”
“blue”
“M.Ramm”
1972
“Mercedes”
“4 door”
“green”
“D.Ramm”
1971
“Datsun”
“2 door”
“red”
“K.Ramm”
1978
“Ford”
“4 door”
“blue”
“D.Ramm”
1978
CompSci 001
12.10