I note that StringBuilder indirectly implements Appendable.
Appendable.append(CharSequence) throws the checked exception IOException. So how does AbstractStringBuilder.append(CharSequence) get away with not declaring IOException? Consequently, how is it that I never have to worry about IOException when I append to a StringBuilder?
Is this some odd exception just for existing classes that have been retrofitted for Appendable, or am I forgetting part of my basic Java rules?
When implementing an interface you may not throw an exception, so you can the following:
new Appendable() {
@Override
public Appendable append(CharSequence charSequence) {
return null;
}
@Override
public Appendable append(CharSequence charSequence, int i, int i1) {
return null;
}
@Override
public Appendable append(char c) {
return null;
}
}
When implementing an interface or extending an abstract class, you can decide whether to throw an exception or not.
An overriding method can throw any unchecked exceptions, regardless of whether the overridden method throws exceptions or not. However, the overriding method should not throw checked exceptions that are new or broader than the ones declared by the overridden method.
AbstractStringBuldercan throw at most anIOExceptionor lower (more specific, subclass ofIOException). The JLS 8.4.8.3. Requirements in Overriding and Hiding for that:"... a method declaration m2 in B overrides or hides a method declaration m1 in A. Then: If m2 has a throws clause that mentions any checked exception types, then m1 must have a throws clause, or a compile-time error occurs..."Appendableyou will have to