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Methods and Parameters Chapter 5 How to split large programs into isolated sections. Focus on one part of the problem – which can be “called” on or “invoked”

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Presentation on theme: "Methods and Parameters Chapter 5 How to split large programs into isolated sections. Focus on one part of the problem – which can be “called” on or “invoked”"— Presentation transcript:

1 Methods and Parameters Chapter 5 How to split large programs into isolated sections. Focus on one part of the problem – which can be “called” on or “invoked” by name

2 paper.drawRect (10, 20, 60, 60); drawRect is called and passed a starting x,y value and an ending x,y value

3 Writing your own methods Page 62-63 “LogoMethod” program private void drawLogo (Graphics drawingArea, int xPos, int yPos) { –Method header for drawLogo method –Formal parameter list inside parenthesis Private method may be called by another method in the same class Void = drawLoge returns nothing, other methods may return any type. Body of method will be enclosed by { }

4 Calling a method drawLogo ( paper, 10, 20); Call must include name of method and arguments (in correct order, number, type) –If any are required

5 Formal vs. Actual parameters Formal parameters in list –drawLogo (Graphics drawingArea, int xPos, int yPos) –drawingArea, xPos and yPos are formal Actual parameters are given in call… –drawLogo ( paper, 10, 20); –Paper, 10 and 20 are Actual

6 Trianglemethod Page 68-69 Page 70 drawTriangle2 (80, 100) (80, 100 + 70)(80 + 60, 100 + 70) W = 60 H = 70

7 Scope local vs. class Pages 71-72 Name Clashes x, y, z may exist locally in any method, even if they are declared as different types Java treats them a different

8 Event handling Called by Java run time system main called automatically actionPerformed called when buttons clicked (or another even occurs) A return sends a result back to the rest of the program. Page 73 program “AreaMethod” returns a value “area” to the calling method answer = areaRectangle ( 30, 40);

9 “drawHouse” page 76-77 Using drawtriangle and drawRectangle to draw a house

10 actionPerformed calls drawHouse drawHouse calls drawRect drawHouse calls drawTriangle drawTriangle calls drawLine areaHouse calls areaRectanglr and areaTriangle adds the results, returns the sum.

11 overloading areaTriangle has an int and a double version based upon the call (int or double) Java decides which to use by type passed in the call

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