Why shortValue() method are concrete but intValue() is abstract into java.lang.Number?

Question

I have read source code of java.lang.Number and I wondered why

1. intValue()
2. longValue()
3. floatValue()
4. doubleValue()

are abstract but

1. shortValue()
2. byteValue()

a concrete.

source code:

public abstract class Number implements java.io.Serializable {

      public abstract int intValue();

      public abstract long longValue();

      public abstract float floatValue();

      public abstract double doubleValue();

      public byte byteValue() {
        return (byte)intValue();
      }

     public short shortValue() {
        return (short)intValue();
      }

    private static final long serialVersionUID = -8742448824652078965L;
}

Why java founders have made it so?

I don't see big differencies between these method. Its seem as related.

P.S.

from Long class:

  public byte byteValue() {
        return (byte)value;
    }


    public short shortValue() {
        return (short)value;
    }


    public int intValue() {
        return (int)value;
    }


    public long longValue() {
        return (long)value;
    }


    public float floatValue() {
        return (float)value;
    }


    public double doubleValue() {
        return (double)value;
    }

from Integer class

public byte byteValue() {
        return (byte)value;
    }


    public short shortValue() {
        return (short)value;
    }


    public int intValue() {
        return value;
    }


    public long longValue() {
        return (long)value;
    }


    public float floatValue() {
        return (float)value;
    }

    public double doubleValue() {
        return (double)value;
    }

Hence we are see a lot of same code. I think copy paste development is bad but I think that Java founders have reasons for this.

Answer 1

According to the documentation of the Number class, the methods byteValue and shortValue were added first in JDK1.1. This is unlike the other "Value" methods which were already available in the very first JDK release. My assumption is that those two methods were made concrete in order to keep compatibility with existing (also non-standard) subclasses of Number, which would otherwise have been broken by the addition of new abstract methods in the superclass.

Answer 2

byte and short are the lesser memory consuming versions, and since intValue is abstract, the implementation of intValue can be used for the byte and short. I think that's why they should have done it like that.