Objects, Methods

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Objects, Methods Multimedia

• CS 026 Lab4

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Java Method

• A method is a named collection of statements that
  have a specific purpose
• How to define a method (object method)
• visibility returnType name (parameterList)
• body of method (a collection of statements)
• The keyword static (class method)
• visibility static returnType name
  (parameterList)
• body of method (a collection of statements)

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Java Method (contd)

• visibility public and private
• returnType such as int, double, void
• name the name of the method, starting with a
  lowercase word and uppercasing the first letter
  of each additional word
• Parameter list specifies the values passed in to
  the method

• public void makeSquare (int length)
• this.turnRight()
• this.forward(length)
• this.turnRight()
• this.forward(length)
• this.turnRight()
• this.forward(length)
• this.turnRight()
• this.forward(length)

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Object Method (Instance Method)

• Can be thought of as a message sent to an object,
  to do something
• Must be executed on an object belonging to the
  class in which the method was defined
• turtle1 is a object of Turtle class, forward() is
  a predefined in Turtle class
• Invoke object method objName.methodName()
• turtle1.forward(100)forward() is a object method

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Class Method (Static Method)

• Can be thought of as a message sent to a class,
  to do something
• Does not need to be executed on an object
  belonging to the class
• static double max (double a, double b) in class
  Math.
• Invoke class method className.methodName()
• Math.max(5.0, 15.5) max() is a class method in
  class Math

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Digital Pictures

• A collection of pixels
• Each pixel has a red, green, and blue value (RGB
  value)
• To manipulate a picture, we manipulate the pixels
  that make up the picture (such as change the
  value of pixel using setRed(), setGreen(),
  setBlue() )

For example Pixel 1 (0, 0) Pixel 2 (0,1) .
How about pixels? (0, 4), (1, 4), (2, 0) --out
of boundary!
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Documentation(part of Java Language)

• For all predefined classes in DrJava
• \intro-prog-java\bookClasses\doc
• For predefined Turtle class in DrJava
• /intro-prog-java/bookClasses/doc/Turtle.html
• For predefined Picture and Pixel classes in
  DrJava
• /intro-prog-java/bookClasses/doc/Picture.html
• /intro-prog-java/bookClasses/doc/Pixel.html
• For predefined class in Java 5
• http//java.sun.com/j2se/1.5.0/docs/api/

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QUESTION?