COMP 110COMP 110Some notes on inheritance, reviewSome notes on inheritance, review

Luv KohliDecember 1, 2008

MWF 2-2:50 pmSitterson 014

AnnouncementsAnnouncementsFinal exam, comprehensive◦Saturday, December 6, 4pm

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Questions?Questions?

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Final examFinal examFinal exam will cover everything we have

covered◦Lectures◦Readings from textbook◦Labs◦Programs◦ In-class exercises/worksheets◦Midterm

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Final exam review on WednesdayFinal exam review on WednesdayNo formal reviewLook over previous assignments, lectures,

midterm, etc.Come prepared with questions

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Today in COMP 110Today in COMP 110Revisiting the equals method

Array and inheritance review

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The The instanceofinstanceof operator operatorWe can test whether an object is of a

certain class type:

if (obj instanceof Student){ System.out.println("obj is an instance of the class

Student");}

Syntax:object instanceof Class_Name

Use this operator in the equals method

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The The equalsequals method methodThird try

public boolean equals(Object obj){ if ((obj != null) && (obj instanceof Student)) { Student otherStudent = (Student) obj; return (this.id == otherStudent.id); } return false;}

Reminder: null is a special constant that can be assigned to a variable of a class type – means that the variable does not refer to anything right now

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The The equalsequals method method Implements an equivalence relation:

It is reflexive◦ For any non-null reference value x, x.equals(x) should return

true

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The The equalsequals method method It is symmetric

◦ For any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true

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The The equalsequals method method It is transitive

◦ For any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true

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The The equalsequals method method It is consistent

◦ For any non-null reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified

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The The equalsequals method methodFor any non-null reference value x, x.equals(null) should

return false

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The The equalsequals method methodThis implementation is not symmetric

public boolean equals(Object obj){ if ((obj != null) && (obj instanceof Student))

{ Student otherStudent = (Student) obj; return (this.id == otherStudent.id); } return false;}

Demonstrate in jGRASP

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The The equalsequals method methodWhy?◦ The instanceof operator will return true if obj is a subclass

of Student

public boolean equals(Object obj){ if ((obj != null) && (obj instanceof Student)) { Student otherStudent = (Student) obj; return (this.id == otherStudent.id); } return false;}

Demonstrate problem in jGRASP

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The The equalsequals method method Fourth try

public boolean equals(Object obj){ if (this == obj) return true; if ((obj == null) || (obj.getClass() != this.getClass())) return false;

Student otherStudent = (Student) obj; return (this.id == otherStudent.id);}

The getClass method will return the runtime class of an object, so if obj is a subclass of Student (in this case), this method will return false

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COMP110 Battle … of DoomCOMP110 Battle … of Doom

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Lazy LennyWeapon/Special ability:

sleep

MagicalFlying amphibianWeapon/Special ability:

fly, make smoke, disappearVS

WINNER

COMP110 Battle … of DoomCOMP110 Battle … of Doom

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SpringWeapon/Special ability:

allergies

MagicalFlying amphibianWeapon/Special ability:

fly, make smoke, disappearVS

WINNER

It’s tough to fly when you are suffering from

allergies!

COMP110 Battle … of DoomCOMP110 Battle … of Doom

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SpringWeapon/Special ability:

allergies

StarburstManWeapon/Special ability:

http://seattlest.com/2008/09/23/local_man_assaulted_by_starburst_ca.php

VS

WINNER

Array and Inheritance review worksheetArray and Inheritance review worksheet

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WednesdayWednesdayFinal exam review

Come prepared with questions!

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