Announcements. Lab 03 inbase late submissions Midterm #1 Friday. Project 2 is posted. Covers everything through basics of OOP

Transcription

1 Announcements Lab 03 inbase late submissions Midterm #1 Friday Covers everything through basics of OOP Project 2 is posted Due next Wednesday All about nested loops good exam practice Coding style is part of the grade Evan Golub s slides Avoiding Redundant code

2 Basics of Object Oriented Programming Cont d

3 The keyword Refers to whichever object is currently executing the instruction Class Memory Object 01 x 3 Object 02 x -1 Object 03 x 101

4 public class MyObj { //A sample class definition int data; //instance field public MyObj(int dat) { //Constructor this.data = dat; //Instance methods public void grow(int more) { this.data = this.data + more; public void gift(myobj other) { other.data = other.data + this.data; this.data = 0;

5 public class MyObj { //A sample class definition int data; //instance field public MyObj(int dat) { //Constructor this.data = dat; //Instance methods public void grow(int more) { this.data = this.data + more; public void gift(myobj other) { other.data = other.data + this.data; this.data = 0;

6 //A main method somewhere else public static void main(string[] args) { MyObj = new MyObj(1); MyObj = new MyObj(2); MyObj obj3 = new MyObj(3);.grow(3);.grow(3);.gift();

7 //A main method somewhere else public static void main(string[] args) { MyObj = new MyObj(1); MyObj = new MyObj(2); data

8 //A main method somewhere else public static void main(string[] args) { MyObj = new MyObj(1); MyObj = new MyObj(2); dat 1 data

9 public class MyObj { //A sample class definition public MyObj(int dat) { //Constructor this.data = dat; dat 1 data

10 public class MyObj { //A sample class definition public MyObj(int dat) { //Constructor this.data = dat; dat 1 data 1 this.data

11 //A main method somewhere else public static void main(string[] args) { MyObj = new MyObj(1); MyObj = new MyObj(2); data 1

12 //A main method somewhere else public static void main(string[] args) { MyObj = new MyObj(1); MyObj = new MyObj(2); data 1 data

13 //A main method somewhere else public static void main(string[] args) { MyObj = new MyObj(1); MyObj = new MyObj(2); dat 2 data 1 data

14 public class MyObj { //A sample class definition public MyObj(int dat) { //Constructor this.data = dat; dat 2 data 1 data

15 public class MyObj { //A sample class definition public MyObj(int dat) { //Constructor this.data = dat; dat 2 data 1 data 2 this.data

16 //A main method somewhere else public static void main(string[] args) { MyObj = new MyObj(1); MyObj = new MyObj(2); data 1 data 2

17 //A main method somewhere else public static void main(string[] args) { MyObj = new MyObj(2); MyObj obj3 = new MyObj(3); data 1 data 2

18 //A main method somewhere else public static void main(string[] args) { MyObj = new MyObj(2); MyObj obj3 = new MyObj(3); data 1 data 2 obj3 data 3

19 //A main method somewhere else public static void main(string[] args) { MyObj obj3 = new MyObj(3);.grow(3); more 3 data 1 data 2 obj3 data 3

20 //A main method somewhere else public static void main(string[] args) { MyObj obj3 = new MyObj(3);.grow(3); more 3 data 1 data 2 obj3 data 3

21 public class MyObj { public void grow(int more) { this.data = this.data + more; more 3 data 1 data 2 obj3 data 3

22 public class MyObj { public void grow(int more) { this.data = this.data + more; more 3 data 1 data 2 obj3 data 3 this.data

23 public class MyObj { public void grow(int more) { this.data = this.data + more; more 3 data 4 data 2 obj3 data 3 this.data

24 //A main method somewhere else public static void main(string[] args) { MyObj obj3 = new MyObj(3);.grow(3); data 4 data 2 obj3 data 3

25 //A main method somewhere else public static void main(string[] args) {.grow(3);.grow(3); more 3 data 4 data 2 obj3 data 3

26 //A main method somewhere else public static void main(string[] args) {.grow(3);.grow(3); more 3 data 4 data 2 obj3 data 3

27 public class MyObj { public void grow(int more) { this.data = this.data + more; more 3 data 4 data 2 obj3 data 3

28 public class MyObj { public void grow(int more) { this.data = this.data + more; more 3 data 4 data 2 obj3 data 3 this.data

29 public class MyObj { public void grow(int more) { this.data = this.data + more; more 3 data 4 data 5 obj3 data 3 this.data

30 //A main method somewhere else public static void main(string[] args) {.grow(3);.grow(3); data 4 data 5 obj3 data 3

31 //A main method somewhere else public static void main(string[] args) {.grow(3);.gift(); other data 4 data 5 obj3 data 3

32 //A main method somewhere else public static void main(string[] args) {.grow(3);.gift(); other data 4 data 5 obj3 data 3

33 public class MyObj { public void gift(myobj other) { other.data = other.data + this.data; this.data = 0; other data 4 data 5 obj3 data 3

34 public class MyObj { public void gift(myobj other) { other.data = other.data + this.data; this.data = 0; other data 4 data 5 obj3 data 3

35 public class MyObj { public void gift(myobj other) { other.data = other.data + this.data; this.data = 0; other data 4 data 5 obj3 data 3 other.data

36 public class MyObj { public void gift(myobj other) { other.data = other.data + this.data; this.data = 0; other data 4 data 5 obj3 data 3 this.data

37 public class MyObj { public void gift(myobj other) { other.data = other.data + this.data; this.data = 0; other data 4 data 9 obj3 data 3 this.data

38 public class MyObj { public void gift(myobj other) { other.data = other.data + this.data; this.data = 0; other data 4 data 9 obj3 data 3 this.data

39 public class MyObj { public void gift(myobj other) { other.data = other.data + this.data; this.data = 0; other data 0 data 9 obj3 data 3 this.data

40 //A main method somewhere else public static void main(string[] args) {.grow(3);.gift(); data 0 data 9 obj3 data 3

41 Omit the this keyword? If you reference an instance field or method, and omit the this keyword, Java assumes you are referring to the current object. Standard practice is to omit this in all but a few special cases.

42 Omit the this keyword? public class MyObj { //A sample class definition int data; //instance field public MyObj(int dat) { //Constructor this.data = dat; //Instance methods public void grow(int more) { this.data = this.data + more; public void gift(myobj other) { other.data = other.data + this.data; this.data = 0;

43 Omit the this keyword? public class MyObj { //A sample class definition int data; //instance field public MyObj(int dat) { //Constructor data = dat; //Instance methods public void grow(int more) { data = data + more; public void gift(myobj other) { other.data = other.data + data; data = 0;

44 When to use this In a constructor: public MyObj(int dat) { //Constructor data = dat; VS public MyObj(int data) { //Constructor this.data = data; Review shadowing (Lec04 ArgsAndParams and example)

45 When to use this To return the object at the end. Compare: public void grow(int more) { data = data + more; //Somewhere else.grow(3) System.out.println();

46 When to use this To return the object at the end. With: public MyObj grow(int more) { data = data + more; return this; //Somewhere else System.out.println(.grow(3));

47 A brief glance at access modifiers Control whether objects of one type can access members in objects of another type. public: Any object can access private: Only objects of the same type can access Gamble example If bias is a private field in Coin, Gambler objects can t access it.

48 Real-world Objects Integer compareto, intvalue Static elements: parseint BigInteger Factorial without overflow Static elements: ONE, TEN, ZERO valueof, probableprime String charat, indexof, substring Static elements: valueof, format