The generic compiler allows overriding with a different primitive return
type, helpfully adding bridge methods. There is no support for that
behavior in the spec.

frog$ cat -n T.java
     1 interface I {
     2 double m();
     3 }
     4
     5 abstract class J {
     6 int m() { return 2; }
     7 }
     8
     9 class K extends J implements I {
    10 public short m() { return 1; }
    11
    12 public static void main(String[] args) {
    13 K k = new K();
    14 J j = k;
    15 I i = k;
    16 System.out.println(i.m() + " " + j.m() + " " + k.m());
    17 }
    18 }
frog$ newjavac T.java
frog$ jdis K.class
super class K
        extends J
        implements I
{


Method "<init>":"()V"
        stack 1 locals 1
{
                aload_0;
                invokespecial Method J."<init>":"()V";
                return;
}

public Method m:"()S"
        stack 1 locals 1
{
                iconst_1;
                ireturn;
}

public static Method main:"([Ljava/lang/String;)V"
        stack 4 locals 4
{
                new class K;
                dup;
                invokespecial Method "<init>":"()V";
                astore_1;
                aload_1;
                astore_2;
                aload_1;
                astore_3;
                getstatic Field java/lang/System.out:"Ljava/io/PrintStream;";
                new class java/lang/StringBuffer;
                dup;
                invokespecial Method java/lang/StringBuffer."<init>":"()V";
                aload_3;
                invokeinterface InterfaceMethod I.m:"()D", 1;
                invokevirtual Method java/lang/StringBuffer.append:"(D)Ljava/lang/StringBuffer;";
                ldc String " ";
                invokevirtual Method java/lang/StringBuffer.append:"(Ljava/lang/String;)Ljava/lang/StringBuffer;";
                aload_2;
                invokevirtual Method J.m:"()I";
                invokevirtual Method java/lang/StringBuffer.append:"(I)Ljava/lang/StringBuffer;";
                ldc String " ";
                invokevirtual Method java/lang/StringBuffer.append:"(Ljava/lang/String;)Ljava/lang/StringBuffer;";
                aload_1;
                invokevirtual Method m:"()S";
                invokevirtual Method java/lang/StringBuffer.append:"(I)Ljava/lang/StringBuffer;";
                invokevirtual Method java/lang/StringBuffer.toString:"()Ljava/lang/String;";
                invokevirtual Method java/io/PrintStream.println:"(Ljava/lang/String;)V";
                return;
}

public Method m:"()I"
        stack 1 locals 1
{
                aload_0;
                invokevirtual Method m:"()S";
                ireturn;
}

public Method m:"()D"
        stack 2 locals 1
{
                aload_0;
                invokevirtual Method m:"()S";
                i2d;
                dreturn;
}

} // end Class K
frog$