Download Simple Console Output

Simple Console Output
What we will briefly discuss
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System.out.println( … )
System.out.print( … )
System.out.printf( … )
Remember our Lab 0
File: Hello.java
// Hello World application
public class Hello
{
public static void main( String args[] )
{
System.out.println( “Hello world” );
}
}
System.out.println( “Hello World”)
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Typing this in our first lab exercise resulted
with the words Hello World displayed on the
console
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The words “Hello World” is a string and is
used as a parameter to the method called
println
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More on strings, parameters and methods in our
lessons next time
System.out.println( “Hello World”)
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For now, we know that whatever we type
within the quotation marks in
System.out.println( … ) will be displayed
on the console
The console refers to our display screen void
of any graphics or graphical user interface
(GUI) objects (ex. Buttons)
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Think of the console as the black MS-DOS window
or the white output display box of BlueJ
What will be displayed?
File: RevisedHello.java
// Revised Hello World application
public class RevisedHello
{
public static void main( String args[] )
{
System.out.println( “Hello world” );
System.out.println( “Good morning” );
System.out.println( “Java is cool” );
}
}
System.out.println()
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println() will display each string on a
separate line
Hello world
Good Morning
Java is cool
How about using print()?
File: RevisedHello.java
// Revised Hello World application
public class RevisedHello
{
public static void main( String args[] )
{
System.out.print( “Hello world” );
System.out.print( “Good morning” );
System.out.print( “Java is cool” );
}
}
System.out.print()
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print() will NOT print the next string on
a new line
Hello worldGood MorningJava is cool
System.out.print()
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Another example
System.out.println( “Hello world” );
System.out.print( “Good morning” );
System.out.println( “Java is cool”);
System.out.println( “So is our teacher” );
Hello world
Good MorningJava is cool
So is our teacher
Try this…
File: RevisedHello.java
// Revised Hello World application
public class RevisedHello
{
public static void main( String args[] )
{
System.out.print( “Hello world” + “\n” );
System.out.print( “Good morning” + “\n” );
System.out.print( “Java is cool” + “\n” );
}
}
Using print() with “\n”
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Even if print() does not display
consecutive strings in separate lines,
the “\n” character causes a line break
The same effect of println() can be
achieved
Now try this…
File: AdvancedExample.java
// A demonstration of printf()
public class AdvancedExample
{
public static void main( String args[] )
{
double pi = Math.PI;
System.out.println( pi );
}
}
//note: pi is a variable assigned to the value of pi.
//Math.PI is a constant value from Math.java
//More on this in our future lessons
Formatting numbers
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The code will display
3.141592653589793 on the console
What if we want to force pi to be
displayed with up to just 3 decimal
places?
System.out.printf()
File: AdvancedExample.java
// A demonstration of printf()
public class AdvancedExample
{
public static void main( String args[] )
{
double pi = Math.PI;
System.out.printf("pi = %5.3f \n", pi);
}
}
System.out.printf()
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The line
System.out.printf("pi = %5.3f \n", pi);
will cause pi to be displayed as 3.142
Format Specifiers
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Indicates how the arguments should be
processed and where they should be inserted
Syntax
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% - start of the specifier
arg_index + '$' (optional)
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position of argument in the argument list
flags (optional)
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provides special formatting (e.g. left align, padding with
zeroes)
Format Specifiers
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Syntax (continued)
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width (optional)
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minimum number of spaces to print argument
puts blanks in unused spaces
'.' + precision (optional)
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number of digits after decimal
conversion – how the
argument should be
formatted
WE WILL DISCUSS THIS INS
DETAIL IN OURFUTURE
LESSONS ON STRINGS
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Conversion
Formatted into:
d
integers
f
floating-point
number
s
String
c
character
The same concept simplified…
System.out.printf("pi = %5.3f \n", pi);
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The % symbol signifies the start of the
specifier
5 means that the width value of the number
is 5 characters
The precision value 3 means that 3 decimal
places are required
The conversion character f means that the
resulting pi is a floating-point number
\n results in a line break