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Chapter 4

Chapter 4. Method parameters Formal and Actual parameters Method returns Encapsulation ‘private’ access modifier ‘public’ getters and setters Instance vs Local variables. Parameters. public class Library{ public static void main(String [] args){

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Chapter 4

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  1. Chapter 4 • Method parameters • Formal and Actual parameters • Method returns • Encapsulation • ‘private’ access modifier • ‘public’ getters and setters • Instance vs Local variables

  2. Parameters public class Library{ public static void main(String [] args){ Book book1 = new Book(“John Fish”, “Die Hard”, 25.69); } }

  3. Parameters public class Library{ public static void main(String [] args){ Book book1 = new Book(“John Fish”, “Die Hard”, 25.69); } } Actual Parameter 1

  4. Parameters public class Library{ public static void main(String [] args){ Book book1 = new Book(“John Fish”, “Die Hard”, 25.69); } } Actual Parameter 2

  5. Parameters public class Library{ public static void main(String [] args){ Book book1 = new Book(“John Fish”, “Die Hard”, 25.69); } } Actual Parameter 3

  6. Parameters public class Book{ String author, title; double price; Book( String a, String b, double c ){ author = a; title = b; price = c; } } Formal Parameter 1

  7. Parameters public class Book{ String author, title; double price; Book( String a, String b, double c ){ author = a; title = b; price = c; } } Formal Parameter 2

  8. Parameters public class Book{ String author, title; double price; Book( String a, String b, double c ){ author = a; title = b; price = c; } } Formal Parameter 3

  9. Parameters public class Library{ public static void main(String [] args){ Book book2 = new Book(“J. Cox”, “Jaws”, 13); } }

  10. Parameters public class Library{ public static void main(String [] args){ Book book2 = new Book(“J. Cox”, “Jaws”, 13); } } Is the 3rd actual parameter legal?

  11. Parameters public class Library{ public static void main(String [] args){ Book book2 = new Book(“J. Cox”, “Jaws”, 13); } } Is the 3rd actual parameter legal? Yes… implicit widening conversion: int > double

  12. Parameters public class Library{ public static void main(String [] args){ Book book2 = new Book(“J. Cox”, “Jaws”, 2 * 14.1f / 3 - 1); } } Is the 3rd actual parameter legal?

  13. Parameters public class Library{ public static void main(String [] args){ Book book2 = new Book(“J. Cox”, “Jaws”, 2 * 14.1f / 3 - 1); } } Is the 3rd actual parameter legal? Yes… expression is evaluated before passing

  14. Parameters public class Book{ String author, title; double price; Book( String a, String b, byte c ){ author = a; title = b; price = c; } } Change formal parameter to byte

  15. Parameters public class Library{ public static void main(String [] args){ Book book2 = new Book(“J. Cox”, “Jaws”, 62); } } Is the 3rd actual parameter legal?

  16. Parameters public class Library{ public static void main(String [] args){ Book book2 = new Book(“J. Cox”, “Jaws”, 62); } } Is the 3rd actual parameter legal? No… implicit narrowing conversion DOES NOT WORK in method invocations

  17. Instance vs. Local variables public class Fun{ public static void main(String [] args){ inti = 0; addTwo( i++ ); System.out.println( i ); } static void addTwo( inti ){ i += 2; } } What is the output?

  18. Instance vs. Local variables public class Fun{ public static void main(String [] args){ inti = 0; addTwo( i++ ); System.out.println( i ); } static void addTwo( inti ){ i += 2; } } i != i main의 i = addTwo의 i

  19. Instance vs. Local variables public class Fun{ public static void main(String [] args){ inti = 0; addTwo( i++ ); System.out.println( i ); } static void addTwo( inti ){ i += 2; } } 1 ! Actual parameter and formal parameter are not the same variables

  20. public class ChefTestDrive{ public static void main(String[] args){ Chef me = new Chef(); me.bakeCookies( 5 ); me.bakeCookies( 2 ); me.makeGimchi( “hot” ); me.makeGimchi( “sweet” ); } } Write this in eclipse and add the Chef class Mmm. 5 delicious cookies Mmm. 2 delicious cookies Oh! Gimchi is too hot! Oh! Gimchi is too sweet!

  21. Method Returns • void go(){ • }

  22. Method Returns • int go(){ • return 5; • }

  23. Method Returns • int go(){ • int x = 5; • return x; • }

  24. Method Returns • String go(){ • String x = “hello buddy”; • return x; • }

  25. Method Returns • long go(){ • int x = 5; • return x; • }

  26. Method Returns • byte go(){ • short x = 5; • return x; • } 불범! implicit narrowingconversion does not work for method returns

  27. Method Returns • Dog go(){ • Dog x = new Dog(); • return x; • }

  28. Encapsulation class Soju { int 술; }

  29. Encapsulation class Soju { int 술; } class SojuTestDrive { public static void main(String[] args){ Soju ohMyGod = new Soju(); ohMyGod.술 = 90; } } What? 90% 술?

  30. Encapsulation class Soju { int 술; }

  31. Encapsulation class Soju { private int 술; }

  32. Encapsulation class Soju { private int 술; void set술(int x){ 술 = x; } } setter method

  33. Encapsulation class Soju { private int 술; void set술(int x){ if(x<45){ 술 = x; } else{ System.out.print(“안돼!”); } } }

  34. Encapsulation class SojuTestDrive { public static void main(String[] args){ Soju ohMyGod = new Soju(); ohMyGod.set술(90); } } 안돼!

  35. Encapsulation class Soju { private int 술; void set술(int x){ … } int get술(){ return 술; } } getter method

  36. Encapsulation class SojuTestDrive { public static void main(String[] args){ Soju ok = new Soju(); ok.set술(20); System.out.print(ok.get술()); } }

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