Download OOP_Course03

OBJECT ORIENTED
PROGRAMMING
Course 3
Loredana STANCIU
[email protected]
Room B613
THE NUMBERS CLASSES
´
Primitive
P
i iti ttypes tto d
define
fi variables:
i bl
« int i = 2;
« float
fl t j
j;
« double d;
´
Wrapper classes for each of the primitive data types
´ Wrap the primitive type in an object
´ Often, the wrapping is done by the compiler
´
´
´
´
Integer x, y;
x = 12;
y = 15;
System.out.println(x+y);
y
p
( y);
THE NUMBERS CLASSES
´
All of the numeric wrapper classes are
subclasses of the abstract class Number
THE NUMBERS CLASSES
´
Why tto use a Number object
Wh
bj t rather
th th
than a
primitive?
« As
an argument of a method that expects an object
« To use constants defined by the class
class, such as
MIN_VALUE and MAX_VALUE, that provide the
upper and lower bounds of the data type.
type
« To use class methods for various conversions
METHODS IMPLEMENTED BY ALL SUBCLASSES
OF NUMBER
´
Converts the value of this Number object to the
primitive data type returned.
« byte byteValue()
« short
h t shortValue()
h tV l ()
« int intValue()
« long longValue()
« float
fl t fl
floatValue()
tV l ()
« double doubleValue()
()
METHODS IMPLEMENTED BY ALL SUBCLASSES
OF NUMBER
´
Compares this Number object to the argument.
« int
« int
« int
« int
« int
« int
compareTo(Byte anotherByte)
compareTo(Double anotherDouble)
compareTo(Float anotherFloat)
compareTo(Integer anotherInteger)
compareTo(Long anotherLong)
compareTo(Short anotherShort)
METHODS IMPLEMENTED BY ALL SUBCLASSES
OF NUMBER
« boolean
equals(Object obj)
Determines
D
t
i
whether
h th this
thi number
b object
bj t iis
equal to the argument.
´ The methods return true if the argument is not
null and is an object of the same type and with
the same numeric value.
´
CONVERSION METHODS,
METHODS INTEGER CLASS
« static
´
Returns an integer (decimal only).
« String
St i
´
t
toString()
St i ()
Returns a String object representing the value
of this Integer.
« static
´
int p
parseInt(String
g s)
String toString(int i)
Returns a String object representing the
specified integer.
CONVERSION METHODS,
METHODS INTEGER CLASS
« static
´
Returns an Integer object holding the value of
the specified primitive.
primitive
« static
´
Integer
g
valueOf(int i)
Integer valueOf(String s)
Returns an Integer object holding the value of
the specified string representation.
FORMATTING NUMERIC PRINT OUTPUT
´
The java.io package includes a
PrintStream class
« System.out.println(String
s)
« System
System.out.format(String
out format(String format
format,
Object... args)
« System.out.printf(String
System out printf(String format,
format
Object... args)
« System.out.format(Locale
f
(
l l
l, String
i
format, Object... args)
FORMATTING NUMERIC PRINT OUTPUT
´
System.out.format("The
S
t
t f
t(" h value
l
of
f
the float variable is %f, " + "
" the value of the integer " +
, and the " +
" variable is %d,
"string is %s", floatVar,
intVar stringVar);
intVar,
´
http://java.sun.com/javase/6/docs/api/java
/util/Formatter html
/util/Formatter.html
FORMATTING NUMERIC PRINT OUTPUT
int i = 461012;
;
´ System.out.format("The value of
i i
is: %d%
%d%n",
" i)
i);
´ The output:
p The value of i is: 461012
´ float floatVar = 3.14;
´ System.out.format(Locale.FRANCE,
S t
t f
t(L
l FRANCE
"The value of the float variable
is %f%n", floatVar);
´ The output: The value of the float
´
variable is: 3,14
FORMATTING NUMERIC PRINT OUTPUT
long n = 461012;
´ System.out.format(
System.out.format("%d%n",
%d%n , n);
´ System.out.format("%08d%n", n);
´ System.out.format("%+8d%n", n);
´ System.out.format(
System out format("%
%,8d%n
8d%n", n);
´ System.out.format("%+,8d%n", n);
´
461012
00461012
+461012
461 012
461,012
+461,012
FORMATTING NUMERIC PRINT OUTPUT
double pi = Math.PI;
´ System.out.format(
System.out.format("%f%n",
%f%n , pi);
3.141593
´ System.out.format("%.3f%n", pi);
3.142
´ System.out.format("%10.3f%n", pi);
3.142
´ System.out.format(
System out format("%-10
% 10.3f%n
3f%n", pi); 3.142
3 142
´ System.out.format(Locale.FRANCE, 3,1416
¹"%-10.4f%n%n", pi);
« import java.util.
java util *;;
´
ADVANCED MATHEMATICAL COMPUTATION
´
´
´
´
´
´
´
´
´
import ja
java.lang.Math.*;
a lang Math *
int abs(float f)
int round(float f)
int min(int
(
arg1,
g , int arg2)
g )
int max(int arg1, int arg2)
double
double
double
double
exp(double d)
log(double d)
pow(double
p
(
base,
, double exponent)
p
)
sqrt(double d)
ADVANCED MATHEMATICAL COMPUTATION
´
´
´
´
´
´
´
´
double
double
double
double
double
double
double
double
sin(double d)
cos(double d)
tan(double d)
asin(double
(
d)
)
acos(double d)
atan(double d)
toDegrees(double d)
toRadians(double d)
ADVANCED MATHEMATICAL COMPUTATION
´
Random Numbers
N mbers
random() method returns a pseudo-randomly selected
number between 0.0 and 1.0 (exclusively)
´
int number = (int)(Math.random() * 10);
´
SUMMARY OF NUMBERS
´
´
´
´
Wrapper classes
W
l
– Byte,
B
Double,
D bl Fl
Float, Integer,
I
LLong,
or Short – to wrap a number of primitive type in an
object
bj
The Number classes include constants and useful
class methods
To format a stringg containingg numbers for output,
p , yyou
can use the printf() or format() methods in the
PrintStream class
The Math class contains a variety of class methods for
performing mathematical functions
CHARACTERS
´
´
char
h primitive
i iti ttype — Character
Ch
wrapper class
l
The Character class is immutable, so that once it is
created, a Character object cannot be changed.
´
Creatingg an Character object:
j
Character ch = new Character('a');
´
autoboxing or unboxing
autoboxing—or
´
«
«
´
Character test(Character c) {...}
char
h
c = t
test('x');
t(' ')
java.lang.Character
CHARACTERS
boolean
b
l
i
isLetter(char
tt ( h
ch)
h)
´ boolean isDigit(char
g (
ch)
)
´ boolean isWhiteSpace(char ch)
´ boolean isUpperCase(char ch)
´ boolean isLowerCase(char ch)
´ char toUpperCase(char ch)
´ char toLowerCase(char ch)
´ toString(char ch)
´
STRINGS
A sequence of characters — objects in the
Java programming language
´ How to create a String?
´
« String
greeting = "Hello
Hello world!";
world! ;
« String
St i
s = new String(greeting);
St i (
ti )
« char[]
c={'h','e','l','l','o','.'};
« String
g S = new String(c);
g( );
STRINGS
The String class is immutable
´ accessor methods — methods used to obtain
information about an object
´
String palindrome = "Dot saw I
was Tod";
T d"
´ int len = palindrome.length();
p
g
´
STRINGS
´
´
´
´
´
´
char[]
h [] tempCharArray
t
Ch A
= new char[len];
h [l ]
char[] charArray = new char[len];
f
for
(i
(int
t i = 0;
0 i < len;
l
i ) {
i++)
« tempCharArray[i] = palindrome.charAt(i); }
for (int j = 0;
0 j < len; j++) {
« charArray[j] = tempCharArray[len - 1 - j];
}
String reversePalindrome = new
String(charArray);
System.out.println(reversePalindrome);
STRINGS
Concatenate Strings
´ string1.concat(string2);
´ "My name is ".concat("Ana");
´
´
"Hello," + " world" + "!"
to span lines in source files
´ String s="Now
s= Now is the time“
time +
°
" of roses.";
´
CONVERTING BETWEEN NUMBERS AND
STRINGS
´
Converting Strings to Numbers
´
Number.valueOf()
« float
a = (Float.valueOf(args[0]) ).floatValue();
« float
oat b = (Float.valueOf(args[1])
( oat a ueO (a gs[ ]) ).floatValue();
) oat a ue();
´
Number.parsePrimitive()
« float
f
a = Float.parseFloat(args[0]);
0
« float b = Float.parseFloat(args[1]);
CONVERTING BETWEEN NUMBERS AND
STRINGS
´
Converting Numbers to Strings
int i;
´ String s1 = "" + i;
´
´
String s2 = String.valueOf(i);
int i;
´ double d;
´ String s3 = Integer.toString(i);
´ String s4 = Double.toString(d);
´
CONVERTING BETWEEN NUMBERS AND
STRINGS
´
´
public
bli class
l
T
ToStringDemo
St i D
{
« public static void main(String[] args) {
² double
d bl d = 858.48;
858 48
² String s = Double.toString(d);
² int dot = s.indexOf('.');
² System.out.println(dot + " digits before
d i l point.");
decimal
i t ")
² System.out.println( (s.length() - dot 1) + " digits after decimal point
point.");
);
« }
}
MANIPULATING CHARACTERS IN A STRING
String aPal = "Niagara
Niagara. O roar
again!";
´ char aChar = aPal.charAt(9);
´
MANIPULATING CHARACTERS IN A STRING
String aPal = "Niagara
Niagara. O roar
again!";
´ String r =aPal.substring(11,15);
´
SEARCHING FOR CHARACTERS AND
SUBSTRINGS IN A STRING
´ String[] split(String regex)
´
C
a Seque ce subSeque
ce( t
CharSequence
subSequence(int
beginIndex, int endIndex)
´
String trim()
´
String
i
toLowerCase()
()
´
String toUpperCase()
SEARCHING FOR CHARACTERS AND
SUBSTRINGS IN A STRING
´ int indexOf(int ch)
int lastIndexOf(int ch)
´ int
i t indexOf(int
i d Of(i t ch,
h int
i t fromIndex)
f
I d )
int lastIndexOf(int ch, int fromIndex)
´ int indexOf(String str)
int lastIndexOf(String str)
´ int indexOf(String str, int fromIndex)
int lastIndexOf(String str, int fromIndex)
´ boolean contains(CharSequence
(
q
s))
SEARCHING FOR CHARACTERS AND
SUBSTRINGS IN A STRING
´
public class Filename {
« private String fullPath;
« p
private char p
pathSeparator,
p
, extensionSeparator;
p
;
«
public Filename(String str, char sep, char ext) {
² fullPath = str;
² pathSeparator = sep;
² extensionSeparator = ext; }
«
public String
p
g extension()
() {
² int dot =
fullPath.lastIndexOf(extensionSeparator);
² return
t
f ll th
fullPath.substring(dot
b t i (d t + 1)
1); }
«…
SEARCHING FOR CHARACTERS AND
SUBSTRINGS IN A STRING
´
…
«
public String filename() {
² int dot =
fullPath.lastIndexOf(extensionSeparator);
² int sep = fullPath.lastIndexOf(pathSeparator);
² return fullPath.substring(sep + 1,
1 dot); }
«
public String path() {
int sep = fullPath.lastIndexOf(pathSeparator);
return fullPath.substring(0, sep);
}
«
«
«
´
}
SEARCHING FOR CHARACTERS AND
SUBSTRINGS IN A STRING
String fpath = "/home/mem/index
html";;
/home/mem/index.html
Filename myHomePage = new Filename(fpath, '/', '.');
Extension = html
´ Filename
Fil
= iindex
d
´
REPLACING CHARACTERS AND SUBSTRINGS
INTO A STRING
String replace(char oldChar, char newChar)
´ String replace(CharSequence target,
q
replacement)
p
)
CharSequence
´ String replaceAll(String regex, String
replacement)
´ String replaceFirst(String regex, String
replacement)
´
COMPARING STRINGS AND PORTIONS OF
STRINGS
´
boolean endsWith(String suffix)
boolean
b l
startsWith(String
t t With(St i g prefix)
fi )
int compareTo(String anotherString)
´ int
i compareToIgnoreCase(String
T I
C
(S i str))
´
boolean equals(Object anObject)
´ boolean equalsIgnoreCase(String anotherString)
´
THE JAVA I/O SYSTEM
import java.io.
java.io.*;;
´ I/O operations based on streams
´
« Input
streams
« Output streams
´
Standard I/O
« System.in
System in
« System.out
« System.err
THE JAVA I/O SYSTEM
´
´
´
IInputt and
d Output
O t t - Source
S
and
dD
Destination
ti ti
The terms "input" and "output" can sometimes be a bit
confusing
Java's IO package concerns with:
«
«
´
the reading of raw data from a source
the writing of raw data to a destination
The typical sources and destinations of data:
«
«
«
«
«
Files
Pipes
Network Connections
In-memory Buffers (e.g. arrays)
S t
System.in,
i System.out,
S t
t System.error
S t
THE JAVA I/O SYSTEM
A program that needs to read data — an input
stream or Reader
´ A program that needs to write data — an output
stream or writer
´ An InputStream or Reader is linked to a
source of data.
´ An OutputStream or Writer is linked to a
destination of data.
´
THE JAVA I/O SYSTEM
´
Java IO Purposes and Features
«
«
«
«
«
«
«
«
«
«
File Access
Network Access
Internal Memory Buffer Access
Inter-Thread Communication (Pipes)
Buffering
Filtering
Parsingg
Reading and Writing Text (Readers / Writers)
Readingg and Writingg Primitive Data ((long,
g, int etc.))
Reading and Writing Objects
THE JAVA I/O SYSTEM
´
Th InputStream
The
S
class:
l
«
«
´
´
´
´
´
the base class of all input streams in the Java IO API
used for reading byte based data, one byte at a time
The FileInputStream class — read the contents of
a file as a stream of bytes
InputStream input = new
FileInputStream("c:\\data\\input-text.txt");
int data = input.read();
while(data != -1)
« {doSomethingWithData(data);
« data = input.read();}
input.close();
THE JAVA I/O SYSTEM
´
´
´
´
´
´
The R
Th
Reader
d iis the
h baseclass
b
l
off allll R
Reader's
d ' in
i the
h Java
J
IO API — BufferedReader
Reader reader = new FileReader();
int data = reader.read();
while(data != -1){
« char dataChar = (char) data;
« data = reader.read(); }
Can be combined with an InputStream — wraped into
InputStreamReader
Reader reader = new
InputStreamReader(inputStream);
THE JAVA I/O SYSTEM
´
´
´
´
´
´
The InputStreamReader
Th
S
d class
l
is
i iintended
t d d tto wrap
an InputStream, thereby turning the byte based
i
input
stream iinto a character
h
b
based
dR
Reader.
d
InputStream inputStream = new
Fil I
FileInputStream("c:\\data\\input.txt");
tSt
(" \\d t \\i
t t t")
Reader reader = new
InputStreamReader(inputStream);
int data = reader.read();
while(data != -1){
1){
« char theChar = (char) data;
« data
d t = reader.read();
d
d() }
reader.close();
THE JAVA I/O SYSTEM
Reading text lines
´ BufferedReader — readLine()
´
« Reads
from an input stream until the line end
« Returns a reference to a String without the line
end or null
« IOException
p
is throwed if no readingg done
´
The constructor needs an object of
InputStreamReader
if reading from a file
« System.in if reading from the console
« FileInputStream
THE JAVA I/O SYSTEM
´
BufferedReader r_in
r in = new BufferedReader(new
InputStreamReader(new
FileInputStream(file name)));
FileInputStream(file_name)));
´
BufferedReader r_in = new BufferedReader(new
(
InputStreamReader (System.in));
´
li = r_in.readLine();
line
i
dLi ()
THE JAVA I/O SYSTEM
´
Th PrintStream
The
i
class:
l
« Enables
the writingg of formatted data to an
underlying OutputStream
« Contains
the print()/println() to print a string
« Contains the powerful format() and printf() methods
´
The constructor needs
Th
d an object
bj
off
FileOutputStream (write a file as a
stream of bytes)
THE JAVA I/O SYSTEM
´
PrintStream w_out = new PrintStream (new
FileOutputStream(file_name));
´
w_out.println(“…”);
´
w_out.print(true);
´
w out print((int) 123);
w_out.print((int)
´
w_out.print((float) 123.456);
´
w_out.printf(Locale.UK, "Text + data: %1$",
123);
´
w_out.close();
THE JAVA I/O SYSTEM
´
Streams and Readers / Writers need to be
closed properly
´
r_in.close( );
´
w out close( );
w_out.close(
´
public static void main (String[
] arg) throws IOException {
´
…
´
}
REFERENCES
´
´
The Java
Th
J
Tutorials.
T
i l Learning
L
i the
h Java
J
LLanguage.
http://java.sun.com/docs/books/tutorial/java/data
/i d h l
/index.html
Java IO Tutorial. http://tutorials.jenkov.com/javaio/index.html