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Access Control

Access Control. All fields may be used in body of class All methods may be used in body of class Access outside of class controlled by : Public Private Protected Package. Access Control. If not specified, package access is assumed

hakeem-ingram
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Access Control

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  1. Access Control All fields may be used in body of class All methods may be used in body of class Access outside of class controlled by : Public Private Protected Package

  2. Access Control • If not specified, package access is assumed • Package access is an operating system function. You must have read rights to directory containing package and files within it.

  3. Top Level Classes • Accessible within package. • If public, accessible by everyone

  4. Member Access • By default, members are accessible through out package • If public, member accessible anywhere • If private, only available within class • If protected, available to • All classes with package • Within subclasses • Between package and public

  5. Member Access • If not specified, it has default package access • Example JHTP ch8 slide 52-59

  6. Expanded method override • public class A { • int i = 1; • int f() {return 1;} • static char g() {return 'A';} • }

  7. public class B extends A { • int i = 2; • int f() {return -1;} • static char g(){return 'B';} • }

  8. public class Test{ • public static void main(String[] args) { • int i1 = 10; • A aa = new A(); • B b = new B(); • A arr[] = new A[4]; • System.out.println("b.i" + b.i); • System.out.println("b.f() = " + b.f()); • System.out.println("b.g() = " + b.g()); • System.out.println("B.g() = " + B.g());

  9. A a = (A) b; • arr[0] = aa; • arr[1] = b; • arr[2] = a;

  10. System.out.println("aa.f() = " + aa.f()); • System.out.println("a.i" + a.i); • System.out.println("a.f() = " + a.f()); • System.out.println("a.g() = " + a.g()); • System.out.println("A.g() = " + A.g()); • System.out.println("arr[0].f() = " + arr[0].f()); • System.out.println("arr[1].f() = " + arr[1].f()); • System.out.println("arr[2].f() = " + arr[2].f()); • System.out.println("end of class"); • System.exit(0); • } • }

  11. Override/Polymorphism • A:\>java Test • b.i2 • b.f() = -1 • b.g() = B • B.g() = B • aa.f() = 1 • a.i1 • a.f() = -1 • a.g() = A • A.g() = A • arr[0].f() = 1 • arr[1].f() = -1 • arr[2].f() = -1 • end of class

  12. Package Example • package cis368; • public class pkgA { • int i = 1; • int f() {return 1;} • static char g() {return 'A';} • }

  13. package cis368; • public class pkgB extends pkgA { • int i = 2; • int f() {return -1;} • static char g(){return 'B';} • }

  14. ┌────────────────────────────── A:\pkgTest.java ────────── • │import cis368.*; • │public class pkgTest{ • │ public static void main(String[] args) { • │ int i1 = 10; • │ cis368.pkgA aa = new cis368.pkgA(); • │ cis368.pkgB b = new cis368.pkgB(); • │ cis368.pkgA arr[] = new cis368.pkgA[4]; • │ System.out.println("b.i" + b.i); • │ System.out.println("b.f() = " + b.f()); • │ System.out.println("b.g() = " + b.g()); • │ System.out.println("pkgB.g() = " + pkgB.g()); • │ pkgA a = (pkgA) b; • │ arr[0] = aa; • │ arr[1] = b; • │ arr[2] = a; • │ System.out.println("aa.f() = " + aa.f()); • │ System.out.println("a.i" + a.i); • │ System.out.println("a.f() = " + a.f()); • │ System.out.println("a.g() = " + a.g()); • │ System.out.println("pkgA.g() = " + pkgA.g()); • │ System.out.println("arr[0].f() = " + arr[0].f()); • │ System.out.println("arr[1].f() = " + arr[1].f()); • │ System.out.println("arr[2].f() = " + arr[2].f()); • │ System.out.println("end of class"); • │ System.exit(0); • │ } • │ }

  15. Errors • A:\>javac pkgTest.java • pkgTest.java:8: i is not public in cis368.pkgB; cannot be accessed from outside • package • System.out.println("b.i" + b.i); • ^ • pkgTest.java:9: f() is not public in cis368.pkgB; cannot be accessed from outsi • e package • System.out.println("b.f() = " + b.f()); • ^ • pkgTest.java:10: g() is not public in cis368.pkgB; cannot be accessed from outs • de package • System.out.println("b.g() = " + b.g()); • ^ • pkgTest.java:11: cannot access pkgB • bad class file: .\pkgB.java • file does not contain class pkgB • Please remove or make sure it appears in the correct subdirectory of the classp • th. • System.out.println("pkgB.g() = " + pkgB.g()); • ^ • 4 errors

  16. A:\>javac pkgA.java • A:\>javac pkgB.java • A:\>copy pkgA.class \cis368\pkgA.class • Overwrite \cis368\pkgA.class? (Yes/No/All): y • 1 file(s) copied. • A:\>copy pkgB.class \cis68\pkgB.class • The system cannot find the path specified. • 0 file(s) copied. • A:\>copy pkgB.class \cis368\pkgB.class • Overwrite \cis368\pkgB.class? (Yes/No/All): y • 1 file(s) copied.

  17. Compiling main • A:\>javac -classpath a:\ pkgTest.java • A:\>

  18. Directory • Directory of A:\ • 02/10/2005 01:35p 97 A.java • 02/10/2005 01:34p 101 B.java • 02/01/2005 03:58p 386 C.java • 02/10/2005 01:35p 312 A.class • 02/10/2005 01:35p 297 B.class • 02/10/2005 01:55p 1,416 Test.class • 02/10/2005 01:54p 859 Test.java • 02/10/2005 01:55p 34 comTest.bat • 02/10/2005 01:56p 11 exeTest.bat • 02/10/2005 02:00p <DIR> cis368 • 02/10/2005 05:34p 143 pkgA.java • 02/10/2005 05:34p 166 pkgB.java • 02/10/2005 05:40p 984 pkgTest.java • 02/10/2005 05:42p 1,448 pkgTest.class • 13 File(s) 6,254 bytes • 1 Dir(s) 1,446,400 bytes free

  19. Running program • A:\>java pkgTest • b.i2 • b.f() = -1 • b.g() = B • pkgB.g() = B • aa.f() = 1 • a.i1 • a.f() = -1 • a.g() = A • pkgA.g() = A • arr[0].f() = 1 • arr[1].f() = -1 • arr[2].f() = -1 • end of class

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