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Map mock question

 
Ranch Hand
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below is from John Myer's

Why does it throw RunTime ClassCastException at line ##??
Object has toString() method, doesn't it?

 
Greenhorn
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This program runs well and prints:
11

If you want it Throw ClassCastException, you need to change

to:



Best,
Yue
 
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Anthony, are you sure you typed it correctly in your editor? The code you gave compiles just fine, and gives output "11".
 
Anthony Karta
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Originally posted by John Johnson:
Anthony, are you sure you typed it correctly in your editor? The code you gave compiles just fine, and gives output "11".



sorry all, it should be put(i, i) not i+"".

anyone can give me explanation? thanks

 
YUE ZHU
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Generics type is about the erasure and cast, so if you mix use the generic and non-generic will compile but will throw RuntimeException.

Rule: generic is compiler magic,it simply erase the type and cast it.

Look at the source code I decompiled from the TestMap:

You see? it Cast the Integer to String, that's why throw ClassCastException.

Best,
Yue
 
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