Topic 04: Graphics

Topic 4 : GraphicsDDOOCP

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Type Casting

› Java is a strongly typed language. This is a very good feature as the programmer is warned that certain combinations of variable or object types are incompatible thus preventing many run time errors.

› But there are some situations when it is desirable to change the type of a variable or object. This process is known as casting.

› Such an action may lead to the loss of information.

› For example, if the double value 12.98 is cast to an integer type then the result would be 12 (the fractional part is lost).

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Type Casting

› Implicit Conversion– automatically converts the one data type into another

› Explicit Conversion

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Implicit Conversion

› An automatic type conversion will be used if the following two conditions are met:

1. The two types are compatible.

2. The destination type is larger than the source type.

• byte –> short –> int –> long –> float –> double

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Explicit Conversion

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› Manual conversion done when the source type is larger than the destination type.

Character to Number and vice-versa

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String to Number and vice-versa

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› The first example is wrong. This is all to do with the distinction between primitive and reference data types.

› Integer and Double are the class. These are Wrapper Class.

› Wrapper classes are used to convert any data type into an object.

Object to Object Casting

› Do you remember JPasswordField is a child of JTextField?

› Since JTextField is parent, JPasswordField is child, we can do :

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CustomButton.java

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Draw the following diagrams

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Graphics Example Template

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Draw a square

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Class java.awt.Graphics

› It is the abstract base class.

1. void setColor(Color c)

2. void setFont(Font font)

3. void drawLine(int x1, int y1, int x2, int y2)

4. void drawRect(int x, int y, int width, int height)

5. void drawRoundRect(int x, int y, int width, int height, int arcWidth, int arcHeight)

6. void drawOval(int x, int y, int width, int height)

7. void drawArc(int x, int y, int width, int height, int startAngle, int arcAngle)

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Class java.awt.Graphics

8. void drawPolygon(int[] xPoints, int[] yPoints, int nPoints)

9. void drawString(String str, int x, int y)

10.void fillRect(int x, int y, int width, int height)

11.void fillRoundRect(int x, int y, int width, int height, int arcWidth, intarcHeight)

12.void fillOval(int x, int y, int width, int height)

13.void fillArc(int x, int y, int width, int height, int startAngle, intarcAngle)

14.void fillPolygon(int[] xPoints, int[] yPoints, int nPoints)

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java.awt.Graphics2D

› void drawString(String str, int x, int y)

› void setStroke(Stroke s)

› void translate(int x, int y)

› void rotate(double angle)

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Draw a circle

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Draw a polygon

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Draw the following diagram

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Draw the following diagram

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Questions

› Explain the difference between casting a string to an integer and using the Integer.parseInt method.

› Assume you are given an array of the numbers 30, 50, 20 and 10. Outline the process by which you could generate a bar chart from this data.

› Explain what is meant by implicit conversion with regards to converting primitive data types to Strings in Java, and provide an example of how to do this in Java.

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References

› http://stackoverflow.com/questions/4049580/what-is-the-difference-between-typecasting-and-typeconversion-in-c-or-java

› http://way2java.com/casting-operations/data-type-casting-type-conversion/

› http://www.java2s.com/Book/Java/0020__Language-Basics/Type_Conversion_and_Casting.htm

› http://way2java.com/java-lang/wrapper-classes/

› http://docs.oracle.com/javase/7/docs/api/java/awt/Graphics.html

› http://docs.oracle.com/javase/7/docs/api/java/awt/Graphics2D.html

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