There seems to be some problems with inference of exception -variables. Javac rejects it, though I don’t quite understand how and why:

 

class Main {
    {
        computeException(this::computeThrowable);
    }

    public <T, E extends Exception> void computeException(ThrowableComputable<T, E> c) throws E {}

    public <E1 extends Throwable> Integer computeThrowable() throws E1 {
        return 0;
    }

    public interface ThrowableComputable<T, E extends Throwable> {
        T compute() throws E;
    }
}

 

 

It looks like javac sees the following bounds

 

var T - upper bounds = java.lang.Object, lower bounds = java.lang.Integer, eq bounds = \n
var E - upper bounds = java.lang.Exception, lower bounds = E1, eq bounds = \n
var E1 - upper bounds = E,java.lang.Exception,java.lang.Throwable, lower bounds = , eq bounds = \n";

 

But I don’t understand why E1 participates in the computeException inference at all.

 

If I remove T from the code, e.g. would define:

public interface ThrowableComputable<T, E extends Throwable> {
    Integer compute() throws E;
}

then javac would accept the code, E1 won’t be included.

 

With the initial sample, if I convert to lambda and extract variable

 

computeException(() -> {
    Integer integer = computeThrowable();
    return integer;
});

 

then code would also compile.