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Protected access

 
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This question builds directly on Question 1.
Assume we have the following code in the file /abc/def/Q.java:
1: //File: /abc/def/Q.java:
2: package def;
3:
4: public class Q {
5: private int privateVar;
6: int packageVar;
7: protected int protectedVar;
8: public int publicVar;
9: }
and this code is in /abc/Tester.java:
1: //File: /abc/Tester.java:
2: import def.Q;
3:
4: public class Tester extends Q {
5: Q sup = new Q();
6: Sub sub = new Sub();
7:
8: public void someMethod() {
9: // First, try to refer to sup's memebers.
10: sup.privateVar = 1; // Line 10
11: sup.packageVar = 2; // Line 11
12: sup.protectedVar = 3; // Line 12
13: sup.publicVar = 4; // Line 13
14:
15: // Next, try to refer to this object's members
16: // supplied by class Q.
17: privateVar = 5; // Line 17
18: packageVar = 6; // Line 18
19: protectedVar = 7; // Line 19
20: publicVar = 8; // Line 20
21:
22: // Next, let's try to access the members of
23: // another instance of Tester.
24: Tester t = new Tester();
25: t.privateVar = 9; // Line 25
26: t.packageVar = 10; // Line 26
27: t.protectedVar = 11; // Line 27
28: t.publicVar = 12; // Line 28
29:
30: // Finally, try to refer to the members in a
31: // subclass of Tester.
32: sub.privateVar = 13; // Line 32
33: sub.packageVar = 14; // Line 33
34: sub.protectedVar = 15; // Line 34
35: sub.publicVar = 16; // Line 35
36: }
37: }
and this code is in /abc/Sub.java:
1: //File: /abc/Sub.java:
2: public class Sub extends Tester {}
According to the explanation for the above code, line 12 won't compile but line 19 will. Can anyone explain why?
 
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This is a bit tricky.
The reason is :
Although protectedVar is inherited by the subclass but the subclass is only allowed to access "it's own" protectedVar. The subclass cannot access super class object's protectedVar. I'm sure this sounds vague but if you read this 6.6.2 Details on protected Access carefully, you'll understand it.
They have also given an example here 6.6.7 Example: protected Fields, Methods, and Constructors

HTH,
Paul.

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[This message has been edited by Paul Anil (edited March 24, 2001).]
 
Michael Burke
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Thanks for the links Paul, that is tricky.
 
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