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Introduction to Programming 1 1
5 Getting Input fromKeyboard
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Introduction to Programming 1 2
Objectives
At the end of the lesson, the student should be able to:
Create an interactive Java program that gets input from the
keyboard Use the BufferedReader class to get input from the
keyboard using a console
Use the JOptionane class to get input from the keyboard
using a graphical user interface
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Introduction to Programming 1 3
Getting Input from the
Keyboard !"o methods of getting input:
BufferedReader class
JOptionane class
graphical user interface
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Introduction to Programming 1 4
Using BufferedReader Class
BufferedReader class
#ound in the $ava%io package
Used to get input
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Introduction to Programming 1 5
teps to get Input&% Add this at the top of your code:
import java.io.*;
'% Add this statement:
BufferedReader dataIn = new BufferedReader( newInputStreamReader( System.in) );
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Introduction to Programming 1 6
teps to get Input(% )eclare a temporary *tring variable to get the input, and
invoke the read+ine- method to get input from thekeyboard% .ou have to type it inside a try/catch block%
try{
String temp = dataIn.readLine();
}catch( IOException e ){System.out.println(Error in getting input);
}
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Introduction to Programming 1 7
ample !rogram1 import java.io.BufferedReader;
2 import java.io.InputStreamReader;
3 import java.io.IOException;
4
5 public class GetInputFromKeyboard {
6
7 public static void main( String[] args ){
8 BufferedReader dataIn = new BufferedReader(new9 InputStreamReader( System.in) );
10
11 String name = "";
12 System.out.print("Please Enter Your Name:");
13 try{
14 name = dataIn.readLine();
15 }catch( IOException e ){16 System.out.println("Error!");
17 }
18 System.out.println("Hello " + name +"!");
19 }
20 }
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Introduction to Programming 1 8
ample !rogram
import java.io.BufferedReader;import java.io.InputStreamReader;
import java.io.IOException;
!he lines,
indicate that "e "ant to use the classes BufferedReader,0nput*treamReaderand 0O12ception"hich are inside the$ava%iopackage%
!hese statements can also be "ritten as,
import java.io.*;
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Introduction to Programming 1 9
ample !rogram
!he Java Application rogramming 0nterface A0- containshundreds of predefined classes that you can use in yourprograms% !hese classes are organi3ed into "hat "e callpackages%
ackagescontain classes that have related purpose%
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Introduction to Programming 1 10
ample !rogram
public class GetInputFromKeyboard {
public static void main( String[] args ){
!he statement,
means "e declare a class named 4et0nput#rom5eyboard
!he ne2t statement declares the main method%
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Introduction to Programming 1 11
ample !rogram
BufferedReader dataIn = new BufferedReader(new InputStreamReader
( System.in) );
!he statement,
declares a variable named dataIn, "ith the class typeBufferedReader%
)on6t "orry about "hat the synta2 means for no"% 7e "ill cover more aboutclasses and declaring classes later in the course%
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Introduction to Programming 1 12
ample !rogram
String name = "";
System.out.print("Please Enter Your Name:");
!he statement,
declares a Stringvariable "ith identifier name.
!he ne2t statement,
outputs a *tring on the screen asking for the user6s name
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Introduction to Programming 1 13
ample !rogram
try{
name = dataIn.readLine();
}catch( IOException e ){
System.out.println("Error!");
}
!he given block defines a try/catch block%
!his assures that the possible e2ceptions that could occur inthe statement
name = dataIn.readLine();
"ill be catched%
7e "ill cover more about e2ception handling in the latter part of thiscourse%
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Introduction to Programming 1 14
ample !rogram
8o" going back to the statement,
the method call, data0n%read+ine-, gets input from the user
and "ill return a *tring value%
!his value "ill then be saved to our namevariable, "hich "e"ill use in our final statement to greet the user,
name = dataIn.readLine();
System.out.println("Hello " + name + "!");
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Introduction to Programming 1 15
Using "option!ane Class
Another "ay to get input from the user is by using theJOptionane class "hich is found in the $ava2%s"ingpackage%
JOptionane makes it easy to pop up a standard dialog bo2that prompts users for a value or informs them of something%
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Introduction to Programming 1 16
ample !rogram1 import javax.swing.JOptionPane;
2
3 public class GetInputFromKeyboard {
4
5 public static void main( String[] args ){
6 String name = "";
7 name=JoptionPane.showInputDialog(Please enter your name");
8 String msg = "Hello " + name + "!";9 JOptionPane.showMessageDialog(null, msg);
10 }
11}
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ample !rogram Output
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ample !rogram
import javax.swing.JOptionPane;
!he statement,
indicates that "e "ant to import the class JOptionane fromthe $ava2%s"ing package%
!his can also "ritten as,import javax.swing.*;
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Introduction to Programming 1 19
ample !rogram
name=JoptionPane.showInputDialog(Please enter your name");
!he statement,
creates a JOptionane input dialog, "hich "ill display adialog "ith a message, a te2tfield and an O5 button as
sho"n in the figure% !his returns a *tring "hich "e "ill save in the name
variable%
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Introduction to Programming 1 20
ample !rogram
String msg = "Hello " + name + "!";
!he statement,
creates the "elcome message, "hich "e "ill store in the
msgvariable%
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Introduction to Programming 1 21
ample !rogram
JOptionPane.showMessageDialog(null, msg);
!he statement,
displays a dialog "hich contains a message and an O5
button%
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ummary
)iscussed t"o "ays of getting input from the user by usingthe classes:
BufferedReader
JOptionane
Brief overvie" of packages
4roups related classes in Java
Classes inside packages can be used by importing the package
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