阅前声明: http://blog.csdn.net/heimaoxiaozi/archive/2007/01/19/1487884.aspx
/****************** Exercise 6 ******************* Create a class with public, private,* protected, and "friendly" data members and* method members. Create an object of this class* and see what kind of compiler messages you get* when you try to access all the class members.* Be aware that classes in the same directory* are part of the "default" package.***********************************************/package c05;public class E06_AccessControl { public int a; private int b; protected int c; int d; // "Friendly" public void f1() {} private void f2() {} protected void f3() {} void f4() {} // "Friendly" public static void main(String args[]) { E06_AccessControl test = new E06_AccessControl(); // No problem accessing everything inside // of main() for this class, since main() // is a member and therefore has access: test.a = 1; test.b = 2; test.c = 3; test.d = 4; test.f1(); test.f2(); test.f3(); test.f4(); }}
//+M java c05.E06_AccessControl
**You can see that main( ) has access to everything because it’s a member. If you create a separate class within the same package, that class cannot access the private members:
// A separate class in the same package cannot // access private elements: package c05; public class E06_Other { public E06_Other() { E06_AccessControl test = new E06_AccessControl(); test.a = 1; //! test.b = 2; // Can't access: private test.c = 3; test.d = 4; test.f1(); //! test.f2(); // Can't access: private test.f3(); test.f4(); } }**If you create a class in a separate package (which you can do either by explicitly giving a package statement, or by simply putting it in a different directory) then it is unable to access anything but public members:
// A separate class in the same package cannot // access private elements: package c05.other2; public class E06_Other2 { public E06_Other2() { c05.E06_AccessControl test = new c05.E06_AccessControl(); test.a = 1; //! test.b = 2; // Can't access: private //! test.c = 3; // Can't access: protected //! test.d = 4; // Can't access: friendly test.f1(); //! test.f2(); // Can't access: private //! test.f3(); // Can't access: protected //! test.f4(); // Can't access: friendly } }