Count set bits in float in Java

This is an interview question: how to count set bits in float in Java ? I guess I should not kno开发者_如何学JAVAw the bit representation of float to answer this question. Can I just convert a float to a byte array somehow? I can use the Java serialization but it looks like overkill.

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The Float class has an:

    public static int floatToIntBits(float value)

method that returns a representation of the specified floating-point value according to the IEEE 754 floating-point "single format" bit layout.

So you can get the bits with this method, then count which ones are set.

http://download.oracle.com/javase/7/docs/api/

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You can use:

Integer.bitCount(Float.floatToIntBits(value))

Having said that it's a very bad interview question...... seems to rely more on knowing specifics of the Java API which is not what you should be using as a basis for hiring. You want someone who understands the principles and knows how to look the details up when needed, not someone who just memorises APIs.

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As well as Java API methods, there's various bit hacks hiding here that you could use as well, although how well they translate to the Java world I don't know (or for those that do, whether they're any more efficient that calling APIs). See the 'Counting bits set' section.