6、异常只能是超类中对应方法所抛出的受检异常的子类。public classSuperClass{ public voidmethodA() throwsIOException{}}public classSubClassAextendsSuperClass{ //this overriding is illegal. private voidmethodA() throws Exception{}}public classSubClassBextendsSuperClass{ //this overriding is OK. public vo
7、idmethodA() throwsFileNotFoundException{}}JAVA语言从Java5开始,子类中的方法的返回值也可以是对应的超类方法的返回值的子类。这叫做“协变”(Covariant)public classSuperClass{ public Numbercaculate(){ return null; }}public class