Using Objects

Java Primitive Data Types

primitive

integral floating point

byte char short int long float double

boolean

Begin with lowercase letters

Java Reference Types

Reference types:

1. String

2. Class name

• int n = greeting.length();

• String bigRiver = river.toUpperCase();

String Methods

What is: Java Syntax??

Variables

int total;

int count, temp, result;

Multiple variables can be created in one declaration

data type

variable name

What Does a Variable Declaration Do?

int ageOfDog;

4 bytes for ageOfDog

initial value in the declaration

Variables

int sum = 0;int base = 32, max = 149;

Assignment

ageOfDog = 10;

Variable Declarations and Assignment of Values

VARIABLE DECLARATIONS

ASSIGNMENT STATEMENTS

•Rules for identifiers in Java?

Identifiers

package movetester;import java.awt.Rectangle; public class MoveTester{ public static void main(String[] args) { Rectangle box = new Rectangle(5, 10, 20, 30); // Move the rectangle where x becomes 20 and y becomes 35 box.translate(15, 25); // Print information about the moved rectangle System.out.println(box.getX()); System.out.print("y: "); System.out.println(box.getY()); System.out.println("Expected: 35"); }}

Packages

•package areatester;

We work with Objects

A fundamental entity in Java.

Objects are “things”

java.lang.Object: the root of java classes

Class Object

Class encapsulates objects

◦work together (behavior)

Objects have properties:

HomeWork P2.1 - Programming Exercise

Graphical User Interfaces

GUI Objects

frame

Content pane used to display objects in a frame

Graphical User Interfaces (GUI): Demonstrates the object concep0t!

01: import javax.swing.JFrame;02: 03: public class EmptyFrameViewer04: {05: public static void main(String[] args)06: {07: JFrame frame = new JFrame();08: 09: frame.setSize(300, 400);10: frame.setTitle("An Empty Frame"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);12: frame.setVisible(true);14: }15: }

Example: Frame Viewer

frame = new JFrame (name); (creates a class instance)

Jframe frame1. Point to object

See Sun site forgreater detail

Sun.java

1. Using the example in your text book on page 64; Section 2.13:

a. Create your own FaceViewer Class with a main method that will show a JComponent.

b. Adjust your Frame to be squarec. The frame title must contain your name.

2. Using the FaceComponent example as a guide (page 64; Section 2.13):

a. Create an Animal Viewer and draw an animal of your choice.

b. Draw a string that describes the animalc. Set colors as desired

Lab 2:Graphical Fun

Lab Completion

Output◦Two classes - tested◦Upload to the appropriate dropbox

Object Lessons?