07-Basic-Input-Output.ppt

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Basic Input and Output

Display output
System.out.println("I'm a string" + " again");
System.out.print("apple");
System.out.print("bananan");
System.out.print("grape");
I'm a string again
applebanana
grape

Input
int c = System.in.read( ); // read 1 byte
byte[] b;
System.in.read( b ); // array of bytes
Scanner console = new Scanner(System.in);
String word = console.next();
String line = console.nextLine();
int number = console.nextInt();
double x = console.nextDouble();
Use a Scanner to read input as int, double, String, etc.
System.in can only read bytes. Not very useful.

Console Output: print
System.out is a PrintStream object.
It has a "print" method to output (display) :
 any primitive data type
 a String
 any Object
int a = 100;
System.out.print("a = "); // print a string
System.out.print(a); // print an int
System.out.print('t'); // print a TAB char
System.out.print("Square Root of 2 = ");
System.out.print(Math.sqrt(2)); // print double
a = 100 Square Root of 2 = 1.4142135623730951

Console Output: println
println is like print, but after printing a value it also
outputs a newline character to move to start of next line.
println can output:
 any primitive type
 a String
 any Object: it automatically calls object.toString()
System.out.println(a); // print an int
System.out.println(); // empty line
System.out.println(1.0/3.0); // print double
a = 100
0.333333333333333

More on print and println
To print several values at once, if the first value is a
String, you can "join" the other values using +
System.out.println("a = " + a);
a = 100
System.out.println(a); // print an int
Is the same as:

Printing an Object
Date now = new Date( );
System.out.println( now );
// invokes now.toString()
If the argument is an object, Java will call the object's
toString() method and print the result.

Common Error
ERROR:
double angle = Math.toRadians(45);
double x = Math.sin(angle);
System.out.println("sin(" , angle ,") = " , x);
mus use + not comma

Formatted Output: printf
Creating nice output using println can be difficult.
public class SalesTax {
public static final double VAT = 0.07; // 7% tax
public static void showTotal( double amount) {
double total = amount * ( 1.0 + VAT );
System.out.println("The total including VAT is "
+total+" Baht");
}
public static void main( String [] args ) {
showTotal(10000);
showTotal(95);
}
}
The total including VAT is 10700.0 Baht

printf
Java 1.5 added a "printf" statement similar to C:
public static void showTotal( double amount) {
double total = amount * ( 1.0 + VAT );
System.out.printf(
"The total including VAT is %8.2f Baht", total);
}
public static void main( String [] args ) {
showTotal(10000);
showTotal(95);
}
Format: output a float (%f) using 8
characters with 2 decimal digits

printf Syntax
The syntax of printf is:
System.out.printf(Format_String, arg1, arg2, ...);
or (no arguments):
System.our.printf(Format_String);
The Format_String can contain text and format codes. Values of
arg1, arg2, are substituted for the format codes.
int x = 100, y = 225;
System.out.printf("The sum of %d and %d is %6dn",
x, y, x+y );
%d is the format code to output
an "int" or "long" value.
%6d means output an integer
using exactly 6 digit/spaces

printf Syntax
Example: print the average
int x = 100, y = 90;
System.out.printf("The average of %d and %d is %6.2fn",
x, y, (x+y)/2.0 );
%6.2f means output a floating point using a
width of 6 and 2 decimal digits.
The average of 100 and 90 is 95.00
%6.2f
%d

Common printf Formats
Format Meaning Examples
%d decimal integers %d %6d
%f fixed pt. floating-point %f %10.4f
%e scientific notation %10e (1.2345e-02)
%g general floating point %10g
(use %e or %f, whichever is more compact)
%s String %s %10s %-10s
%c Character %c
String owner = "Taksin Shinawat";
int acctNumber = 12345;
double balance = 4000000000;
System.out.printf("Account %6d Owner %-18s has %10.2fn",
acctNumber, owner, balance );
Account 12345 Owner Taksin Shinawat has 4000000000.00

More details on printf
 printf is an instance of the Formatter class.
 It is predefined for System.out.
 System.out.printf(...) is same as System.out.format(...).
 For complete details see Java API for "Format".
 For tutorial, examples, etc. see:
 Sun's Java Tutorial
 Core Java, page 61.

String.format
A useful method that creates a String using a format.
/** describe a bank acount */
String name = "John Doe";
long accountId = 12345;
double balance = 123.456;
String result = String.format(
"Acct: %09d Owner: %s Balance: %.2f",
accountId, name, balance );
return result;
Acct: 000012345 Owner: John Doe Balance: 123.46

Input byte-by-byte
System.in is an InputStream object.
It reads data one byte at a time, or an array of bytes.
Use System.in.read( ) to get "raw" data, such as an
image:
int a = System.in.read( );
if (a < 0) /* end of input */;
else {
byte b = (byte)a;
handleInput( b );
}
Boring, isn't it?

Input Line-by-Line
To get a line of input as a String, you can create a
BufferedReader object that "wraps" System.in.
BufferedReader reader = new BufferedReader(
new InputStreamReader( System.in ) );
String s = reader.readLine( ); // read one line
The readLine( ) method removes the NEWLINE (n)
from the input, so you won't see it as part of the string.

Check for end of data
If there is no more data in the input stream, readLine( )
returns a null String.
For console input, readLine( ) will wait (block) until user
inputs something.
Here is how to test for end of data:
String s = reader.readLine( ); // read one line
if ( s == null ) return; // end of data

Handling I/O Errors
When you use System.in.read or a BufferedReader an
input error can occur -- called an IOException.
Java requires that your program either "catch" this
exception to declare that it might "throw" this exception.
To be lazy and "throw" the exception use:
public static void main(String [] args)
throws IOException {
// read a line of input
String inline = reader.readLine( );

Catching I/O Errors
To "catch" the exception and do something, use:
// read a line of input.
// display message and return if error
String line = null;
try {
line = bin.readLine( );
buf.append( line );
}
catch( IOException ioe ) {
System.err.println( ioe.getMessage() );
return;
}

Flexible Input: Scanner class
The Scanner class allow much more flexible input.
A Scanner can:
 read entire line or one word at a time
 test for more data
 test if the next input (word) is an int, long, double, etc.
 read input and convert to int, long, float, double
 skip unwanted data
 report errors (Exceptions) that occur

Import Scanner
Scanner is a "utility" so it is package java.util.
You should import this class to use it:
package myapp;
import java.util.Scanner;
...
public class InputDemo {

Create a Scanner Object
Scanner "wraps" an InputStream.
You give the InputStream object as parameter when you
create a Scanner object...
// create a Scanner to read from System.in
Scanner console = new Scanner( System.in );

Where to Create Scanner object?
1) You can create a Scanner as a local variable
public void myMethod( ) { // no IOException !
// create a Scanner as a local variable
Scanner in = new Scanner( System.in );
// read some different types of data
int count = in.nextInt( );
public class InputDemo {
// create a Scanner as static attribute
static Scanner console =
new Scanner( System.in );
// can use console in any method.
2) or create as an attribute.
Typically a static attribute since System.in is static.

Using Scanner
Look at some simple examples
public void myMethod( ) { // no IOException !
// create a Scanner to process System.in
Scanner in = new Scanner( System.in );
// read some different types of data
int count = in.nextInt( );
long big = in.nextLong( );
float x = in.nextFloat( );
double y = in.nextDouble( );
// read Strings
String word = scan.next( ); // next word
String line = scan.nextLine( ); // next line

Input Errors
If you try to read an "int" but the next input is not an integer
then Scanner throws an InputMismatchException
Scanner scan = new Scanner( System.in );
// read a number
System.out.print("How many Baht? ");
int amount = scan.nextInt( );
How many Baht? I don't know
Exception in thread "main"
java.util.InputMismatchException
convert next input
word to an "int"

How to Test the Input
Scanner has methods to test the next input value:
Scanner scanner = new Scanner( System.in );
int amount;
// read a number
if ( scanner.hasNextInt( ) )
amount = scanner.nextInt( );
else {
System.out.println("Please input an int");
scanner.nextLine(); // discard old input
}
Please input an int
true if the next input
value is an "int"

Testing the input
So now you can check for invalid input.
But, what do you do with the bad input?
If scan.hasNextInt( ) is false, then the program doesn't
read it.
So, the bad input is still waiting to be read. Like this:
Next input value to read.
We want to remove this bad input, so we can ask the
user to try again. ...what should we do?

Discarding the input
If the input is wrong, then throw it away by reading the
line and discarding it.
get the input line but don't assign
it to anything! (discard it)
int amount;
// read a number
if ( scanner.hasNextInt( ) )
amount = scanner.nextInt( );
else {
System.out.println("Please input an int");
scanner.nextLine(); // discard input

Useful Scanner Methods
Return type Method Meaning
String next() get next "word"
String nextLine() get next line
int nextInt() get next word as int
long nextLong() get next word as long
float nextFloat() get next word as float
double nextDouble() get next word as double
boolean hasNext() true if there is more input
boolean hasNextInt() true if next word can be "int"
boolean hasNextLong() true if next word can be "long"
boolean hasNextFloat() true if next word can be "float"
boolean hasNextDouble() true if next word can be
"double"
See Java API for java.io.Scanner for a complete list of methods.

Input/Output Example
Read some numbers and output their sum...
double sum = 0.0;
// prompt user for input
System.out.print("Input some numbers: ");
// read as long as there are more numbers
while ( scanner.hasNextDouble( ) ) {
double x = scanner.nextDouble( );
sum = sum + x;
}
System.out.println();
System.out.println("The sum is "+sum);

TUGAS
Implementasikan contoh-contoh listing program pada
materi dan dikumpulkan.
- isi dari tugas adalah listing program dan hasil output
dari listring tersebut
- tugas dibuat dalam kelompok yang terdiri dari 4 orang
- tuliskan nama-nama anggota kelompok pada lembar
pertama tugas

07-Basic-Input-Output.ppt

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