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Using Objects
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Java Primitive Data Types
integral boolean floating point byte char short int long float double Begin with lowercase letters
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Java Reference Types Reference types: 1. String 2. Class name
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String Methods int n = greeting.length();
String bigRiver = river.toUpperCase();
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What is: Java Syntax??
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Multiple variables can be created in
variable name data type int total; int count, temp, result; Multiple variables can be created in one declaration
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What Does a Variable Declaration Do?
int ageOfDog; 4 bytes for ageOfDog
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Variables initial value in the declaration int sum = 0;
int base = 32, max = 149;
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Assignment ageOfDog = 10;
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Variable Declarations and Assignment of Values
ASSIGNMENT STATEMENTS
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Identifiers Rules for identifiers in Java?
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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"); } }
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Packages package areatester;
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We work with Objects A fundamental entity in Java.
Objects are “things”
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java.lang.Object: the root of java classes
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Class Object Class encapsulates objects work together (behavior)
Objects have properties:
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HomeWork P2.1 - Programming Exercise
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Graphical User Interfaces
GUI Objects
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Graphical User Interfaces (GUI): Demonstrates the object concep0t!
frame Graphical User Interfaces (GUI): Demonstrates the object concep0t! Content pane used to display objects in a frame
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Example: Frame Viewer 01: import javax.swing.JFrame; 02:
03: public class EmptyFrameViewer 04: { 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: } (page 56 of text) or section 2.11 Example: Frame Viewer
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frame = new JFrame (name);
Jframe frame Point to object frame = new JFrame (name); (creates a class instance)
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See Sun site for greater detail Sun.java
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Lab 2:Graphical Fun Using the example in your text book on page 64; Section 2.13: Create your own FaceViewer Class with a main method that will show a JComponent. Adjust your Frame to be square The frame title must contain your name. Using the FaceComponent example as a guide (page 64; Section 2.13): Create an Animal Viewer and draw an animal of your choice. Draw a string that describes the animal Set colors as desired
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Upload to the appropriate dropbox
Output Two classes - tested Upload to the appropriate dropbox Lab Completion
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Object Lessons?
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