[Thinking in Java] modifier public,protected, default, private

When using Java, often encounter four kinds of modifiers, namely public,protected, default (no modifier), private, here write down their differences public: In-Package outside the package access

Protected: In-package access, out-of-package only subclass access

Default: Any access within the package

Private: In-class access only

Explain in code

1  PackageP1;2 Import Staticjava.lang.system.*;3 4  Public classA {5      Public intM1 = 1;6     protected intM2 = 2;7     intM3 = 3;8     Private intM4 = 4;9     Ten      Public voidF1 () { OneOut.println ("F1"); A     } -     protected voidF2 () { -Out.println ("F2"); the     } -     voidF3 () { -Out.println ("F3"); -     } +     Private voidf4 () { -Out.println ("F4"); +     } A      at     voidDemo () { - OUT.PRINTLN (M1); - out.println (m2); - out.println (m3); - Out.println (M4); -          in F1 (); F2 (); F3 (); F4 () ; -          tob b =NewB (); +     } -      the      Public Static voidMain (string[] args) { *         NewA (). Demo (); $     }Panax Notoginseng } -  the classB { +      PublicB () { AOut.println ("Class B"); the     } +}

P1. A

1  PackageP1;2 Import Staticjava.lang.system.*;3 4  Public classC {5     voidDemo () {6A A =NewA ();7 out.println (A.M1);8 out.println (a.m2);9 out.println (a.m3);Ten         //out.println (A.M4); One          A a.f1 (); A.f2 (); a.f3 (); -         //a.f4 (); -          the         //the default class can be used within the same package -b b =NewB (); -     } -      +      Public Static voidMain (string[] args) { -         NewC (). Demo (); +     } A}

P1. C

 PackageP2;Importp1.*;Import Staticjava.lang.system.*; Public classD {voidDemo () {A A=NewA ();        Out.println (A.M1); //none of the following can be accessed//out.println (A.M2); //out.println (A.M3); //out.println (A.M4);a.f1 (); //none of the following can be called//A.f2 (); //a.f3 (); //a.f4 (); //default classes cannot be used within other packages//b b = new B ();    }         Public Static voidMain (string[] args) {NewD (). Demo ();    E.main (args); }}classEextendsa{//subclasses of a    voidDemo () {OUT.PRINTLN (M1); Out.println (Super. M1); Out.println (NewA (). M1);        Out.println (m2); Out.println (Super. m2); //out.println (New A (). m2);//failed//out.println (A.M3); //out.println (A.M4);F1 ();        F2 (); Super. F2 (); //new A (). F2 ();//failed//a.f3 (); //a.f4 (); //default classes cannot be used within other packages//b b = new B ();    }         Public Static voidMain (string[] args) {NewE (). Demo (); }}

P1. D

[Thinking in Java] modifier public,protected, default, private