limited generic type

I'm trying to create a generic class that accepts only two types (i.e., Integers and Doubles), as if I would make the class with only Double type, I would be wasting space when I would use the same class for object having only int fields.

Here is the code:

public class Freq implements Comparable {
private String term;
public double frequency;

public String getTerm() {
    return term;
}

public void setTerm(String term) {
    this.term = term;
}

public Freq( String term, int frequency ) {
this.term = term;
this.frequency = frequency;
}

public int compareTo(Object arg) {
    if(this.frequency == ((Freq)arg).frequency)
        return 0;
    else if( this.frequency  >  ((Freq)arg).frequency ) {
        return 1;
    }
    else 
        return -1;
}

Now as you can see this class has the mem开发者_如何转开发ber frequency as double, but I would like to leave that generic but limited to only doubles and integers. However, if I add the generic type such as <T extends Number>, then compareTo method is failing (it says that operator > is not defined on Numbers or T, ...), and I couldnt figure it out why, hence I need your help.

thanks in advance

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You could make it fully generic by using something like this:

public class Freq<N extends Number & Comparable<N>> implements Comparable<Freq<N>> {

  private final N frequency;

  public Freq(N frequency) {
    if (frequency == null) {
      throw new IllegalArgumentException("frequency must be non-null");
    }
    this.frequency = frequency;
  }

  public int compareTo(Freq<N> other) {
    return frequency.compareTo(other.frequency);
  }
}

But if object size is your primary concern, then this might not be the best solution, as you need to store a reference to the wrapper object (Double or Integer) in addition to the object itself, which is almost certainly larger than just storing a double itself.

Thus implementing a simple Frequency class that only provides double values might actually help safe space.

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You can't use primitives for generic types. You can however store any int value in a double, so I would just use a double for everything.

BTW: You may find this simpler

public class Freq implements Comparable<Freq>
  public int compareTo(Freq freq) {
    return Double.compare(frequency, freq.frequency);
  }

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Generics don't mix with primitive types. So either you must use types derived from Number (which means you can't use > anymore because that works only with primitives) or you can't use generics.

One solution is not to use int. double is 64bit and can contain any value that int can have. Also, since the int's never have a fraction casting from and do double won't cause loss of precision or rounding errors.

So you can write a class IntFreq which wraps Freq and casts all values accordingly.

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Try to use this.frequency.doubleValue() for the comparison.