Download Basic Input

Console Input
So far…
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All the inputs for our programs have
been hard-coded in the main method or
inputted using the dialog boxes of BlueJ
It’s time to get input straight from the
user.
Our topic: Console Input
What is a console?
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Console input
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Any input that is entered in the console
window
Not typed in a dialog box
Programming for input
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Like printing out, getting input requires calls to Java packages
java.io.InputStream - stores information about the
connection between an input device and the computer or
program.
java.io.InputStreamReader - used to translate data bytes
received from InputStream objects into a stream
of characters.
java.io.BufferedReader - used to temporarily store (buffer)
the input received from a InputStreamReader object.
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Improves efficiency
Input devices are much slower than the computer's processor and
buffering the data reduces the number of times the CPU has to
interact with the device itself.
Steps for console input
1.
2.
3.
4.
5.
Use the System.in object to create an
InputStreamReader object.
Use the InputStreamReader object to
create a BufferedReader object.
Display a prompt to the user for the desired
data.
Use the BufferedReader object to read a
line of text from the user.
Do something interesting with the input
received from the user.
Sample
import java.io.*;
public class HelloAgainWithInput {
public static void main ( String args[] ) throws
Exception
{
String s;
InputStreamReader stdin =
new InputStreamReader(System.in);
BufferedReader console =
new BufferedReader(stdin);
System.out.print( "What's your name? ");
s = console.readLine();
System.out.println( "Hello, " + s );
}
}
Sample
Imports the Java packages that you need:
•InputStream
•InputStreamReader
•BufferedReader
import java.io.*;
public class HelloAgainWithInput {
public static void main ( String args[] ) throws
Exception
{
String s;
InputStreamReader stdin =
new InputStreamReader(System.in);
BufferedReader console =
new BufferedReader(stdin);
System.out.print( "What's your name? ");
s = console.readLine();
System.out.println( "Hello, " + s );
}
}
Sample
Declare the class
import java.io.*;
public class HelloAgainWithInput {
public static void main ( String args[] ) throws
Exception
{
String s;
InputStreamReader stdin =
new InputStreamReader(System.in);
BufferedReader console =
new BufferedReader(stdin);
System.out.print( "What's your name? ");
s = console.readLine();
System.out.println( "Hello, " + s );
}
}
Sample
import java.io.*;
This ignores input errors; we’ll
deal with those later.
public class HelloAgainWithInput {
public static void main ( String args[] ) throws
Exception
{
String s;
InputStreamReader stdin =
new InputStreamReader(System.in);
BufferedReader console =
new BufferedReader(stdin);
System.out.print( "What's your name? ");
s = console.readLine();
System.out.println( "Hello, " + s );
}
}
Sample
import java.io.*;
public class HelloAgainWithInput {
public static void main ( String args[] ) throws
Exception
{
Declare a string to hold the input
String s;
InputStreamReader stdin =
new InputStreamReader(System.in);
BufferedReader console =
new BufferedReader(stdin);
System.out.print( "What's your name? ");
s = console.readLine();
System.out.println( "Hello, " + s );
}
}
Sample
import java.io.*;
public class HelloAgainWithInput {
public static void main ( String args[] ) throws
Exception
Create a new InputStreamReader
{
String s;
InputStreamReader stdin =
new InputStreamReader(System.in);
BufferedReader console =
new BufferedReader(stdin);
System.out.print( "What's your name? ");
s = console.readLine();
System.out.println( "Hello, " + s );
}
}
Sample
import java.io.*;
public class HelloAgainWithInput {
public static void main ( String args[] ) throws
Exception
{
Create a new BufferedReader
String s;
InputStreamReader stdin =
new InputStreamReader(System.in);
BufferedReader console =
new BufferedReader(stdin);
System.out.print( "What's your name? ");
s = console.readLine();
System.out.println( "Hello, " + s );
}
}
Sample
import java.io.*;
public class HelloAgainWithInput {
public static void main ( String args[] ) throws
Exception
{
String s;
We use a
InputStreamReader stdin =
print, not a
new InputStreamReader(System.in);
println, so
BufferedReader console =
that there is no
new BufferedReader(stdin);
carriage return
System.out.print( "What's your name? ");
at the end of
s = console.readLine();
the line.
System.out.println( "Hello, " + s );
}
}
Prompt the user for input
Sample
import java.io.*;
public class HelloAgainWithInput {
public static void main ( String args[] ) throws
Exception
{
We use a
String s;
readLine.
InputStreamReader stdin =
There is a
new InputStreamReader(System.in);
read method
BufferedReader console =
also that reads
new BufferedReader(stdin);
a single
System.out.print( "What's your name? ");
character—not
s = console.readLine();
what we want.
System.out.println( "Hello, " + s );
}
}
Read the input
Sample
import java.io.*;
public class HelloAgainWithInput {
public static void main ( String args[] ) throws
Exception
{
String s;
InputStreamReader stdin =
new InputStreamReader(System.in);
BufferedReader console =
new BufferedReader(stdin);
System.out.print( "What's your name? ");
s = console.readLine();
System.out.println( "Hello, " + s );
}
}
Do something with the input
Sample 2: Numeric input
import java.io.*;
public class HelloWithNumbers {
public static void main ( String args[] ) throws Exception
{
String s;
int age;
int yearBorn;
InputStreamReader stdin =
new InputStreamReader(System.in);
BufferedReader console =
new BufferedReader(stdin);
System.out.print( "What's your name? ");
s = console.readLine();
System.out.println( "Hello, " + s );
System.out.print( "How old are you? ");
s = console.readLine();
age = Integer.parseInt( s );
yearBorn = 2006 - age;
System.out.println( "You were born in " + yearBorn);
}
}
Sample 2: Numeric input
import java.io.*;
public class HelloWithNumbers {
public static void main ( String args[] ) throws Exception
{
String s;
int age;
int yearBorn;
InputStreamReader stdin =
new InputStreamReader(System.in);
BufferedReader console =
new BufferedReader(stdin);
System.out.print( "What's your name? ");
s = console.readLine();
System.out.println( "Hello, " + s );
System.out.print( "How old are you? ");
Converts a
s = console.readLine();
an integer
age = Integer.parseInt( s );
yearBorn = 2006 - age;
System.out.println( "You were born in " + yearBorn);
}
}
string to
Exercise
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Write a program that will get two
integers, m and n, from the user. The
program will then display a rectangle
with m rows and n columns of made of
“*”.
A static console
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It is likely you will use console input for Java
applications with a main method
If you need to use it in other methods in the
application besides main, have a static
BufferedReader variable (called console, for
example) and then you may reuse that
variable in other methods
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Instantiate it upon declaration
private static BufferedReader console =
new BufferedReader( new InputStreamReader
( System.in ) );
Using a static console
import java.io.*;
public class HelloWithNumbers {
private static BufferedReader console =
new BufferedReader(new InputStreamReader(System.in));
public static void main ( String args[] ) throws Exception
{
String s;
int age;
int yearBorn;
System.out.print( "What's your name? ");
s = console.readLine();
System.out.println( "Hello, " + s );
System.out.print( "How old are you? ");
s = console.readLine();
age = Integer.parseInt( s );
yearBorn = 2006 - age;
System.out.println( "You were born in " + yearBorn);
}
// can use console in other methods you define here …
}