Lectures / lecture3_1
.pdfAPPLICATION DEVELOPMENT
SDP-2
Lecture 4.
Brodyagina Mariya
Quiz
Which statement is true?
a.There are eight primitive types built in to the Java programming language.
b.byte, short, char, and long are the four integral primitive data types in the Java programming language.
c.A boolean type variable holds true, false, and nil.
d.long=10; is a valid variable name that adheres to the variable declaration and initialization syntax.
Working with Objects: Introduction
Objects are accessed via references.
–Objects are instantiated versions of their class.
–Objects consist of attributes and operations:
•In Java, these are fields and methods.
Accessing Objects by Using a
Reference
The camera is like the object that is accessed via the reference (remote).
The remote is like the reference used to access the camera (object).
Working with Object Reference Variables
• Declaration:
Classname identifier;
This code fragment
Instantiation: |
creates the object. |
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new Classname();
Assignment:
Object reference 
= 
new Classname();
The identifier |
The |
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from the |
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assignment |
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Declaration |
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operator |
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step |
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To assign to a reference, creation and assignment must be in same statement.
Declaring and Initializing: Example
1 Declare a |
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reference for |
2 |
the object. |
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Create the object |
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instance. |
Shirt myShirt;
myShirt = new Shirt();
3 Assign the object to the reference variable.
Working with Object References
Declare and initialize reference.
Shirt myShirt = new Shirt(); |
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int shirtId = myShirt.shirtId; |
Get the value of |
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the shirtId |
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field of the |
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myShirt.display(); |
object. |
Call the display() method of the object.
Working with Object References
1 Create a Shirt object and get a reference to it.
1
Pick up remote to gain access to camera.
2
Press remote controls to have camera do something.
Shirt myShirt = new Shirt();
myShirt.display();
2
Call a method to have Shirt object do something.
Working with Object References
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There is |
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only one |
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remote2 |
Camera |
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object. |
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Camera remote1 = new Camera();
Camera remote2 = remote1;
remote1.play();
remote2.stop();
remote1
References to Different Objects
Television
Television remote
Camcorder
Camcorder remote