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Classes And Objects

Java is strictly an Object-Oriented

Programming Language.

Java code Class

Interface

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Classes

Describe the object’s

attributes behaviors

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Class is a description of anobject.

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Object is defined to be aninstance of a class

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An Object consists of 

attributes

behaviors

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An attribute is a feature of the object,

something the object“has”. 

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A behavior is something

the object “does” 

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Each attribute of an objectis denoted as a field in the

class

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Each behavior of an objectbecomes a method in the

class

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Procedural ProgrammingFlowcharts

Decomposition

Procedures

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Object-Oriented ProgrammingClasses

Objects

Inheritance

Encapsulation

Polymorphism

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Payroll ProgramDetermining objects in problem

• Employees

• Company

• Payroll department• more objects….

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Employee ClassAttributes

name

address

national id number

Behaviors

hours worked()pay()

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Writing a Java class

class (keyword)

public class Employee{

}

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Employee class

public class Employee

{

public String name;public String address;

public String id;

public double hPay;}

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public class Employee

{

public String name;public String address;

public String id;

public double hPay;

public void writeDetails

{

System.out.println(name + “” + id); }

}

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public class Employee

{

public String name;public String address;

public String id;

public double hPay;

public double computePay

{

return hPay * 40;}

}

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public class Vehicle

{

int pasg;int fCap;

int mpg;

}

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Creating Vehicle object

Vehicle jeep = new Vehicle();

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Dot (.) operator

Object.member

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Dot operator

 jeep.fCap = 16;

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Instantiating an Object

Vehicle jeep ;

 jeep = new Vehicle() ;

Create an object in memory

and returns a reference 

reference jeep is pointing to

the Vehicle object in

memory

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  jeep.psg = 8 ;

 jeep.fCap = 24 ;

Jeep.mpg = 44 ;

car.psg = 4 ;

car.fCap = 18 ;

car.mpg = 28 ;

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Constructor

Initializes an object when its created.

Has the same name as its class.

Syntactically similar to a method.

Has no explicit return type.

Give initial values to the instance variables.

Perform startup procedures.

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Constructor

All classes have constructors.

Java automatically defines default constructor

that initializes all member variables to zero.

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Garbage Collection

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Vehicle jeep = new Vehicle()

Vehicle jeep = new Vehicle()

Vehicle jeep = new Vehicle()

Vehicle jeep = new Vehicle()

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Vehicle j1 = new

Vehicle(); j1

Vehicle j2 = new

Vehicle();

 j2Vehicle j3 = j2;

 j3

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Vehicle j1 = new

Vehicle(); j1

Vehicle j2 = new

Vehicle();

 j2Vehicle j3 = j2;

 j3 j1 = j2;

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The finalize() Method

Called just before an object’s final destruction by

the garbage collector.

protected void finalize()

{

 // code

}