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 } }