Professor: Alvin Chao

Transcription

1 Professor: Avin Chao

2 CS149 More with Casses and Objects

3 OverLoading Let's ook at the Car cass...

4 Terminoogy Method definition pubic void acceerate(doube amount) { speed += amount; if (speed > MAX_SPEED) { speed = MAX_SPEED;

5 Terminoogy Method definition Method body Method header pubic void acceerate(doube amount) { speed += amount; if (speed > MAX_SPEED) { speed = MAX_SPEED; speed += amount; if (speed > MAX_SPEED) { speed = MAX_SPEED; { pubic voidacceerate(doube amount)

6 Terminoogy Method definition Method body Method header Method signature pubic void acceerate(doube amount) { speed += amount; if (speed > MAX_SPEED) { speed = MAX_SPEED; speed += amount; if (speed > MAX_SPEED) { speed = MAX_SPEED; pubic voidacceerate(doube amount) { acceerate(doube amount)

7 Quiz #1 pubic cassperson { Person bob= new Person("Bob"); System.out.printn(bob.getName()); pubic Person(String name) { name = name; pubic String getname() { return name; Wi it compie? If so, what wi be printed?

8 Quiz #1 pubic cassperson { Person bob= new Person("Bob"); System.out.printn(bob.getName()); pubic Person(String name) { name = name; pubic String getname() { return name; The name parameter shadows the name fied. Wi it compie? YES If so, what wi be printed? nu

9 Quiz #2 pubic cassperson { Person bob= new Person("Bob"); System.out.printn(bob.toString()); pubic Person(String n) { name = n; pubic String getname() { return name; Wi it compie? If so, what wi be printed?

10 Quiz #2 pubic cassperson { Person bob= new Person("Bob"); System.out.printn(bob.toString()); pubic Person(String n) { name = n; pubic String getname() { return name; Wi it compie? YES If so, what wi be printed? Person@6ff4ff23

11 Quiz #2 pubic cassperson { pubic Person(String n) { name = n; pubic String getname() { return name; Person bob= new Person("Bob"); System.out.printn(bob.toString()); Every cass has a defaut tostring method. The string wi contain the name of the cass and the ocation of the object in memory. (This is usuay not very hepfu.) Wi it compie? YES If so, what wi be printed? Person@6ff4ff23

12 Quiz #3 pubic cassperson { pubic Person(String n) { name = n; pubic String getname() { return name; Person bob= new Person("Bob"); System.out.printn(bob); Wi it compie? If so, what wi be printed? pubic String tostring() { return "Person named: " + name;

13 Quiz #3 pubic cassperson { pubic Person(String n) { name = n; pubic String getname() { return name; pubic String tostring() { return "Person named: " + name; Person bob= new Person("Bob"); System.out.printn(bob); Wi it compie? YES If so, what wi be printed? Person named: Bob The print methods wi automaticay ca the tostring method of any object passed to them.

14 Quiz #4 pubic cassperson { pubic Person(String n) { name = n; pubic String getname() { return name; Person bob1= new Person("Bob"); Person bob2 = new Person("Bob"); System.out.printn(bob1 == bob2); Wi it compie? If so, what wi be printed? pubic String tostring() { return "Person named: " + name;

15 Quiz #4 pubic cassperson { pubic Person(String n) { name = n; pubic String getname() { return name; Person bob1= new Person("Bob"); Person bob2 = new Person("Bob"); System.out.printn(bob1 == bob2); Wi it compie? YES If so, what wi be printed? fase pubic String tostring() { return "Person named: " + name;

16 Quiz #4 pubic cassperson { pubic Person(String n) { name = n; pubic String getname() { return name; pubic String tostring() { return "Person named: " + name; Person bob1= new Person("Bob"); Person bob2 = new Person("Bob"); System.out.printn(bob1 == bob2); Wi it compie? YES If so, what wi be printed? fase == Compares the addresses (references) stored in the two variabes. Two objects two different addresses.

17 Quiz #5 pubic cassperson { pubic Person(String n) { name = n; pubic String getname() { return name; Person bob1= new Person("Bob"); Person bob2 = new Person("Bob"); System.out.printn(bob1.equas(bob2)); Wi it compie? If so, what wi be printed? pubic String tostring() { return "Person named: " + name;

18 Quiz #5 pubic cassperson { pubic Person(String n) { name = n; pubic String getname() { return name; Person bob1= new Person("Bob"); Person bob2 = new Person("Bob"); System.out.printn(bob1.equas(bob2)); Wi it compie? YES If so, what wi be printed? fase pubic String tostring() { return "Person named: " + name;

19 Quiz #5 pubic cassperson { pubic Person(String n) { name = n; pubic String getname() { return name; pubic String tostring() { return "Person named: " + name; Person bob1= new Person("Bob"); Person bob2 = new Person("Bob"); System.out.printn(bob1.equas(bob2)); Wi it compie? YES If so, what wi be printed? fase A casses get a defaut.equas method. It just uses ==.

20 Typica equas Method pubic cassperson { private intssn; pubic Person(String nm, intnum) { name = nm; ssn = num; pubic String getname() { returnname; pubic int getssn() { returnssn; pubic String tostring() { return"person named: " + name; pubic booean equas(person other) { returnname.equas(other.getname()) && ssn == other.getssn(); Compares a fieds.

21 Typica equas Method pubic cassperson { private intssn; pubic Person(String nm, intnum) { name = nm; ssn = num; pubic String getname() { returnname; pubic int getssn() { returnssn; pubic String tostring() { return"person named: " + name; pubic booean equas(person other) { Person bob1= new Person("Bob", 1); Person bob2 = new Person("Bob", 1); Person bob3 = new Person("Bob", 3); Person bob4 = bob2; System.out.printn(bob1.equas(bob2)); System.out.printn(bob1.equas(bob3)); System.out.printn(bob1.equas(bob4)); System.out.printn(bob2.equas(bob4)); System.out.printn(bob1 == bob2); System.out.printn(bob1 == bob3); System.out.printn(bob1 == bob4); System.out.printn(bob2 == bob4); What wi be printed? returnname.equas(other.getname()) && ssn == other.getssn();

22 Typica equas Method pubic cassperson { private intssn; pubic Person(String nm, intnum) { name = nm; ssn = num; pubic String getname() { returnname; pubic int getssn() { returnssn; pubic String tostring() { return"person named: " + name; pubic booean equas(person other) { returnname.equas(other.getname()) && ssn == other.getssn(); Person bob1= new Person("Bob", 1); Person bob2 = new Person("Bob", 1); Person bob3 = new Person("Bob", 3); Person bob4 = bob2; System.out.printn(bob1.equas(bob2)); System.out.printn(bob1.equas(bob3)); System.out.printn(bob1.equas(bob4)); System.out.printn(bob2.equas(bob4)); System.out.printn(bob1 == bob2); System.out.printn(bob1 == bob3); System.out.printn(bob1 == bob4); System.out.printn(bob2 == bob4); What wi be printed? true fase true true fase fase fase true

23 tostring and equas Providing tostring and equas methods shoud be a routine part of deveoping a cass. No tostring method? Compicates testing No equas method? May ead to sneaky bugs (Remember that a broken equas method wi be provided by defaut.)

24 Quiz pubic casscarmain { pubic static voidmain(string[] args) { int resut; String s = "Heo"; System.out.printn(s); resut = nonsense1(s); System.out.printn(s); What wi be printed? Car ford = new Car("Ford", 1992); System.out.printn(ford.getSpeed()); resut = nonsense2(ford); System.out.printn(ford.getSpeed()); pubic static int nonsense1(string word) { word += word; returnword.ength(); pubic static int nonsense2(car car) { car.acceerate(); returncar.getyear();

25 Quiz pubic casscarmain { pubic static voidmain(string[] args) { int resut; String s = "Heo"; System.out.printn(s); resut = nonsense1(s); System.out.printn(s); Car ford = new Car("Ford", 1992); System.out.printn(ford.getSpeed()); resut = nonsense2(ford); System.out.printn(ford.getSpeed()); pubic static int nonsense1(string word) { What wi be printed? Heo Heo word += word; returnword.ength(); pubic static int nonsense2(car car) { car.acceerate(); returncar.getyear();

26 Mutabe vs Immutabe Types Immutabe types Objects can't be changed once created String is an immutabe type Mutabe types An object's fieds may change over time We need to be carefu that our methods don't accidentay modify mutabe objects that are passed as arguments.

27 Acknowedgements Parts of this activity are based on materias deveoped by Chris Mayfied and Nathan Sprague. </end>