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Can anyone explain me what is happening at line 8?  RSS feed

 
Tushar Gosalia
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1.class Mixer {
2.Mixer() { }
3.Mixer(Mixer m) { m1 = m; }
4.Mixer m1;
5.public static void main(String[] args) {
6.Mixer m2 = new Mixer();
7.Mixer m3 = new Mixer(m2); m3.go();
8.Mixer m4 = m3.m1; m4.go();
9.Mixer m5 = m2.m1; m5.go();
}
void go() { System.out.print("hi "); }
}
 
harshvardhan ojha
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At line 8, you are calling no arg constructor that you have defined at line 2.
 
harshvardhan ojha
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also for this reason line number 9, will give you NullPointerException as m2 has no object which you are asking it to return.
 
Tushar Gosalia
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No i'm asking about
Mixer m4 = m3.m1; m4.go();
What does this statement mean??And What will be stored in m4??
 
harshvardhan ojha
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m4 will refer to m2 object, as you kept it in m3 and asking it to return that object.
 
Himai Minh
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Object reference diagram:
m2 -> o where o is an object
m2.m1 -> null
m3 -> o1 where o1 is another object
m3.m1 -> m2 ->o
m4 -> m3.m1-> m2 -> o
m5->m2.m1-> null
So, m5.go() returns a null pointer exception
 
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