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class P {
static void printS1(){System.out.print("P.printS1 ");}
void printS2() {System.out.print("P.printS2 ");}
void printS1S2(){printS1();printS2();}
}
class Q extends P {
static void printS1(){System.out.print("Q.printS1 ");}
void printS2(){System.out.print("Q.printS2 ");}
public static void main(String[] args) {
new Q().printS1S2();
}
}
Result is: P.printS1 Q.printS2
Could anybody explain it? Thanks
 
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printS1 is not overriden(static method can not be overriden but rather, hide-ed/hidden) whereas printS2 is overriden.
And thus dynamic binding is applied to printS2 and not to printS1.
 
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but...
class P {
static void printS1(){System.out.print("P.printS1 ");}
void printS2() {System.out.print("P.printS2 ");}
void printS1S2(){printS1();printS2();}
}
class Q extends P {
static void printS1(){System.out.print("Q.printS1 ");}
void printS2(){System.out.print("Q.printS2 ");}
void printS1S2(){printS1();printS2();} //added by me
public static void main(String[] args) {
new Q().printS1S2();
}
}
result is "Q.printS1 Q.printS2". Why?
[ May 22, 2003: Message edited by: Catherine Jones ]
 
Yi Meng
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my understanding is that:
In the first case, the printS1S2 method is not overriden, when you have new Q().printS1S2();, it actually refers to the one in class P and it will envoke class P's printS1 method.
In the second case, the printS1S2 is overriden. when you have newQ().printS1S2(); it envokes its own(Q's) printS1S2 method and Q's static method printS1 is envoked as P's is hide-ed/hidden.
 
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In the first case, the printS1S2 method is not overriden, when you have new Q().printS1S2();, it actually refers to the one in class P and it will envoke class P's printS1 method.


if this is the reason then y is Q's printS2 invoked. P's printS2 shud have been invoked!


In the second case, the printS1S2 is overriden. when you have newQ().printS1S2(); it envokes its own(Q's) printS1S2 method and Q's static method printS1 is envoked as P's is hide-ed/hidden.

 
Yi Meng
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if this is the reason then y is Q's printS2 invoked. P's printS2 shud have been invoked!


see my previous post? printS2 method is properly overriden and dynamic binding applies whereas printS1 is NOT overriden......
[ May 22, 2003: Message edited by: Yi Meng ]
 
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Here is how I understand it:
Rule: Whenever a non-static method is inherited in a sub-class, any static references made in this method will resolve to implementations in the super class while any non-static references made in this method will resolve to implementations in the sub-class.
 
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Method Q.printS1 hides method P.printS1. Method Q.printS2 overrides method P.printS2. Therefore, method P.printS1S2 invokes P.printS1 and Q.printS2.
Please see Section 8.6.4 of the Java Language Specification.
 
Barkat Mardhani
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In first case, printS1S2 method is inherited. Therefore a call to a static method within it will resolve to super-class and call to non-static method will resolve to sub-class.
In second case, printS1S2 method is overriden. Therefore both calls to static and non-static method is resolved to sub-class.
 
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