About multithreaded access Vector

One thread to access a Vector object :
for (int i = 0; i {Object obj = v.elementAt (i);
......
}

another thread : v.removeElementAt (3)

ask what the problem ?
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Vector thread itself is relatively safe , there would be no big problem.

But you here Object obj = v.elementAt (i); access to the part after the object obj may have been removed from the Vector .
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last may be less a figure, and get out of the incomplete data
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1. obtained data may not be what you want
2. deleted may be incorrect , v may not have three objects
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Vector is a linear safe collection should not be a problem, right