Using Objects
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?