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Begreber og Redskaber 4

Begreber og Redskaber 4. BRP. Plan for idag. Om metoder, parametre, returværdier Et par ord om objekt-orientering Håndkøring af programmer. Håndkøring 1. Application.main args = null i=1 j=3. public class Application{ public static void main(String args[]){ int i,j;

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Begreber og Redskaber 4

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  1. Begreber og Redskaber 4 BRP

  2. Plan for idag • Om metoder, parametre, returværdier • Et par ord om objekt-orientering • Håndkøring af programmer

  3. Håndkøring 1 Application.main args = null i=1 j=3 public class Application{ public static void main(String args[]){ int i,j; i=1; j=3; • while(j>0){ i=i*2; j=j-1; } } }

  4. Håndkøring 1 Application.main args = null i=1 2 j=3 2 public class Application{ public static void main(String args[]){ int i,j; i=1; j=3; while(j>0){ i=i*2; j=j-1; • } } }

  5. Håndkøring 1 Application.main args = null i=1 2 4 j=3 2 1 public class Application{ public static void main(String args[]){ int i,j; i=1; j=3; while(j>0){ i=i*2; j=j-1; • } } }

  6. Håndkøring 1 Application.main args = null i=1 2 4 8 j=3 2 1 0 public class Application{ public static void main(String args[]){ int i,j; i=1; j=3; while(j>0){ i=i*2; j=j-1; • } } }

  7. Metoder i klasser • Klasser kan indeholde metoder - dvs underprogrammer class A{ int i,j; void udskriv(){ System.out.println(i+”,”+j);} } A a = new A(); a.i=7; a.j=3; a.udskriv(); Uddata: 7,3

  8. Virkefelt • Java er blokstruktureret (som Pascal, C...) • Navne kan genbruges i forskellige blokke class A{ int i; void p(){ int i; ...} } Klassen har felt i, metoden lokal variabel i

  9. Funktioner • Metoder kan have returværdi class A{ int i,j; int iogj(){return i+j; } } A a = new A(); a.i=7; a.j=3; System.out.println(a.iogj());} Uddata: 10

  10. Håndkøring 2 Application.main args = null i= j= public class Application{ public static int f(int x,int y){ x++; return x+y+1; } public static void main(String args[]){ int i,j; • i=1; i++; j=f(i,4); } }

  11. Håndkøring 2 Application.main args = null i=1 2 j= public class Application{ public static int f(int x,int y){ x++; return x+y+1; } public static void main(String args[]){ int i,j; i=1; i++; • j=f(i,4); } }

  12. Håndkøring 2 Application.main args = null i=1 2 j= public class Application{ public static int f(int x,int y){• x++; return x+y+1; } public static void main(String args[]){ int i,j; i=1; i++; j=f(i,4); } } f x=2 y=4

  13. Håndkøring 2 Application.main args = null i=1 2 j= public class Application{ public static int f(int x,int y){ x++; • return x+y+1; } public static void main(String args[]){ int i,j; i=1; i++; j=f(i,4); } } f x=2 3 y=4

  14. Håndkøring 2 Application.main args = null i=1 2 j=8 public class Application{ public static int f(int x,int y){ x++; return x+y+1; } public static void main(String args[]){ int i,j; i=1; i++; j=f(i,4); • } } f -> 8 x=2 3 y=4

  15. Eksempel på objekter class A{ int i,j; } .. A a; //a kan have hægte til obj a = new A(); // a peger på obj. a.i = 1; //dot-notation

  16. Oprettelse af objekter • Hvis felter skal initialiseres under oprettelse kan det ske i en konstruktør class A{ int i,j; A(){ i = 0; j = 1; } }

  17. Oprettelse • Argumenter til oprettelsen class A{ int i,j A(int x, int y){ i=x; j = y;} } .... A a = new A(2,3);

  18. Hægter til objekter • Variable med klasse som type er hægter til objekter – initielt null class A{ ... } A a = new A(); A b = a; a A obj. b

  19. this refererer til objektet class A{ private int i; void setI(int i){this.i=i;} int getI(){int i=this.i; return i;} void addToI(int j){i=i+j;} }

  20. Håndkøring 3 Application.main args = null a= b= t= class A{int x;} public class Application { public static void main(String args[]) {A a,b,t; • a=new A(); b=new A(); a.x=1; b.x=2; t=a; a=b; b=t ;}}

  21. Håndkøring 3 Application.main args = null a= b= t= class A{int x;} public class Application { public static void main(String args[]) {A a,b,t; a=new A(); • b=new A(); a.x=1; b.x=2; t=a; a=b; b=t ;}} A X=0

  22. Håndkøring 3 Application.main args = null a= b= t= class A{int x;} public class Application { public static void main(String args[]) {A a,b,t; a=new A(); b=new A(); • a.x=1; b.x=2; t=a; a=b; b=t ;}} A X=0 A X=0

  23. Håndkøring 3 Application.main args = null a= b= t= class A{int x;} public class Application { public static void main(String args[]) {A a,b,t; a=new A(); b=new A(); a.x=1; b.x=2; • t=a; a=b; b=t ;}} A X=0 1 A X=0 2

  24. Håndkøring 3 Application.main args = null a= b= t= class A{int x;} public class Application { public static void main(String args[]) {A a,b,t; a=new A(); b=new A(); a.x=1; b.x=2; t=a; • a=b; b=t ;}} A X=0 1 A X=0 2

  25. Håndkøring 3 Application.main args = null a= b= t= class A{int x;} public class Application { public static void main(String args[]) {A a,b,t; a=new A(); b=new A(); a.x=1; b.x=2; t=a; a=b; • b=t; }} A X=0 1 A X=0 2

  26. Håndkøring 3 Application.main args = null a= b= t= class A{int x;} public class Application { public static void main(String args[]) {A a,b,t; a=new A(); b=new A(); a.x=1; b.x=2; t=a; a=b; b=t; • }} A X=0 1 A X=0 2

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