For converting from the binary to decimal you have to use scintific calculator.But if you want to do paper work then it is difficult to explain here all the method.So you need to study all the stuff about the converting the numbers.
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You can use the method Integer.parseInt(string containing the number in some base, base) method, but pay attention as digits from the string must be included in the radix of the 2nd argument. For example, if you want to parse the string "234122" and the radix is set to 3 you'll get a NumberFormatException exception.