Презентация на тему Java technology classes and objects

of objects, and act as blueprint for creating such

objects.

single whole).
An object has state (it has various properties,

which might change).
An object has behavior (it can do things and can have things done to it).

Object is entity that has the following features:

pen
A Computer The air above Keyboard the keyboard

A shoe The color black
A desk All desks in the world

Is the tube of tennis balls an object?
Is

each tennis ball an object?
Could the top two balls be considered a single object?
Is the color of the balls an object?
Is your understanding of tennis balls an object?

out of?
Answer: Computer memory.
Software objects have

identity because each is a separate chunk of memory having name.
Software objects have state. Some of the memory that makes a software object is used for attributes which contain values.
Software objects have behavior. Some of the memory that makes a software object is used to contain programs (called methods) that enable the object to "do things." The object does something when one of its method runs.

a kind of object.
A programmer may define

a class
or may use predefined classes that come in class libraries.
A class is merely a plan for a possible object (or objects.). It does not by itself create any objects.
When a programmer wants to create an object the new operator is used with the name of the class.
Creating an object is called instantiation.

Methods


“Make discount”,
“Set name”,
“Add photo”

“Add photo”


Object of same class have same

structure, it exhibits properties & behaviors defined by its class.
Properties is also called as attributes/fields & behaviors as methods/operations.

interface

CLASS IN JAVA

и power.
Declare objects auto and moto.
public class Vehicle{
int

speed;
double power;
}

Vehicle auto;
Vehicle moto = null;

Create objects auto and moto by new keyword.

auto = new Vehicle();
moto = new Vehicle();

use an object reference or expression, followed by the

dot (.) operator, followed by a simple field name, as in:

objectReference.fieldName

GET & SET ATTRIBUTES

To get: variable = object.field;
To set: object.field = variable;

fields:
auto.power = 88.7;
auto.speed = 150;
moto.power = 24;
moto.speed =

120;
System.out.println(auto.power +” “+ auto.speed);
System.out.println(moto.power +” “+ moto.speed);
auto.speed = 180;
System.out.println(auto.power +” “+ auto.speed);
System.out.println(moto.power +” “+ moto.speed);

Every object has independent fields.

method. Append the method's simple name to the object

reference, with an intervening dot operator (.). Provide, within enclosing parentheses, any arguments to the method. If the method does not require any arguments, use empty parentheses.

objectReference.methodName(argumentList);
or:
objectReference.methodName();

CALLING METHODS

eff() {
return power/speed;
}
Compare 2 objects
System.out.print(auto.eff()>moto.eff());

The objects must

be created to use method eff().

in Java.
Strings are constants, their values cannot

be changed after they are created. But they can be reinitialized.
String here=“I am here”;
here=“I am there”;//previous one is completely deleted
Our rules and dictionaries can be stored string class.
This class is armed with useful methods

compareTo(String str),
concate(String str),
endsWith(String str),
indexOf(int ch),
length(),
startsWith(String str),
lastIndexOf(String str).

//comp=0;
String lab= “Language”;
lab=lab.concate(“ Technology”); //lab=“Language Technology”;
int ind = machine.indexOf(‘t’);
boolean

start = machine.startsWith(“pen”); //true
boolean end = machine.endsWith(“um”); //true
String part1=machine.substring(0,3); //part1=“pen”;
String part2=machine.substring(5);//part2=“um”;

String[] args ) {
String str1;

// str1 is a variable that refers to an object,
// but the object does not exist yet.
int len; // len is a primitive variable of type int
str1 = new String(“Bullet is waiting…"); // create an object of type String
len = str1.length(); // invoke the object's method length() System.out.println("The string is " + len + " characters long");
}
}

the primitive data types. These classes "wrap" the primitive

in an object.

NUMBER WRAPPERS

int x = 25;
Integer y = new Integer(33);

a Number object rather than a primitive:
As an argument

of a method that expects an object (often used when manipulating collections of numbers).
To use constants defined by the class, such as MIN_VALUE and MAX_VALUE, that provide the upper and lower bounds of the data type.
To use class methods for converting values to and from other primitive types, for converting to and from strings, and for converting between number systems (decimal, octal, hexadecimal, binary).

REASONS

to the primitive data type returned.
CONVERT TO PRIMITIVE TYPES
byte

byteValue() short shortValue() int intValue() long longValue() float floatValue() double doubleValue()

Double Var = new Double (3.1415);
int i = Var.intValue();

compareTo(Byte anotherByte) int compareTo(Double anotherDouble) int compareTo(Float anotherFloat) int compareTo(Integer anotherInteger) int compareTo(Long

anotherLong) int compareTo(Short anotherShort)

Integer Var = new Integer (5);
int i = 3;
if(Var.compareTo(i)) System.out.println (“They are the same!”);
else System.out.println (“They are different!”);

useful for converting numbers to and from strings and

for converting between number systems.

STRING INTO INTEGER

static Integer decode(String s)

Decodes a string into an integer. Can accept string representations of decimal, octal, or hexadecimal numbers as input.

Integer iVar = Integer.decode(“3”);

static int parseInt(String s)

Returns an integer (decimal only).

int i = Integer.parseInt(“3”);

static int parseInt(String s, int radix)

Returns an integer, given a string representation of decimal, binary, octal, or hexadecimal (radix equals 10, 2, 8, or 16 respectively) numbers as input.

int i = Integer.parseInt(“3”,16);

the value of this Integer.
Integer y = 125;
String

s1 = y.toString(); //"125”

static String toString(int i)

Returns a String object representing the specified integer.

String s1 = Integer.toString(25); //"25”

static String toBinaryString(int i)
public static String toOctalString(int i)
public static String toHexString(int i)

Returns a String object representing the specified integer in binary, octal or hexadecimal form.

String s1 = Integer.toBinaryString(12); //“1100”

in decimal integer form and which prints the result

in binary, octal and hexadecimal form.

EXERCISE

frequency and mode (switched on/off). Have methods to change

the mode and to change frequency. In main() method create Radio object and then get user input to change and to print mode & frequency.

HOMEWORK