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COMP 110Static Methods and Variables

Tabitha Peck M.S.

March 24, 2008

MWF 3-3:50 pm

Philips 367

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Announcements

• No Homework… yet

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Questions?

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Today in COMP 110

• Static Methods

• A little review

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Methods

• Actions performed by objects– smiley.drawFace();– this.setColor(“green”);– circumference?– area?

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Static Methods

• Methods that do not require an object of any kind– Where have you seen static before?– Invoke method with class name– SmileyClass.circumference(3);

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Why no object?

• What data is in the object?

• When should you create a static method?

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Writing a static method

• Add static to the heading

public static final double PI = 3.14159; public static double circumference(double radius){

return (PI*(radius + radius));}

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Writing a static method

• Cannot do anything that refers to a calling object– Why?

public static final double PI = 3.14159;private boolean smile = true; public static double circumference(double radius){

smile = false;return (PI*(radius + radius));

}

NO

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Accessing instance variables or methods

• Create an object

public static final double PI = 3.14159;private boolean smile = true; public static double circumference(double radius){

Smiley s = new Smiley();s.drawMouth(false);return (PI*(radius + radius));

}

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Self-Test Questions

• Can you invoke a nonstatic method within a static method?

• Can you invoke a static method within a nonstatic method?

• Can you reference an instance variable within a static method?

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The Math Class

• All methods in this class are static– Don’t create a Math object– Invoke methods using class name Math

• Math.abs• Math.max• Math.min• Math.round

– Predefined constants• Math.PI• Math.E

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• Math.round(2.3)

• Math.round(2.7)

• Math.floor(2.3)

• Math.floor(2.7)

• Math.ceil(2.3)

• Math.ceil(2.7)

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Type Casting with Math

• Ceil returns a double– Math.ceil(5.6) return 6.0

• What do you do if you want an int?

– int num = (int)Math.ceil(5.6);

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Primitive vs. Class Types

• Primitive– int, float, char, double– Stored in memory as value

• Class– String, classes you write– Stored in memory as address

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Objects in Memory

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3.14159

2078

1056

Name: TomAge: 20

int numfloat num2

Person p1

Person p2

Name: JaneAge: 23

p2 = p1;

2078p1.setName(“Joe”);

Name: JoeAge: 23

p2.print();p1.print();

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Methods with objects as arguments

• How is an object stored in memory?

• What is passed as the argument?

• What happens if you modify an object in your method?

• What about primitive types?

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Wrapper Classes

• What if you want a primitive type to be modified in your method?

• Convert a primitive type to an “equivalent” class type– Integer n = new Integer(42);– Integer n = 42;

• EVERY primitive type has a wrapper class

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Wrapper ClassesConstants and Static Methods• Numeric Wrapper Classes

– Integer.MAX_VALUE;– Double.MIN_VALUE;– Float.parseFloat(“23.4”);– Long.toString(368);

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Class Character

• toUpperCase

• toLowerCase

• isUpperCase

• isLowerCase

• isWhiteSpace

• isLetter

• isDigit

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Algebra Review / Writing code

• Write static methods– abs(double n), returns double– ceil(float n), returns double– floor(double n), returns double– max(int n1, int n2), returns int– min(float n1, float n2), returns float– round(float n), returns int

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Wednesday

• Designing and overloading methods

• Read 5.3 and 5.4

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Wednesday