Mega Code Archive
Overridden methods may throw only the exceptions
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// : c09:StormyInning.java
// Overridden methods may throw only the exceptions
// specified in their base-class versions, or exceptions
// derived from the base-class exceptions.
// From 'Thinking in Java, 3rd ed.' (c) Bruce Eckel 2002
// www.BruceEckel.com. See copyright notice in CopyRight.txt.
class BaseballException extends Exception {
}
class Foul extends BaseballException {
}
class Strike extends BaseballException {
}
abstract class Inning {
public Inning() throws BaseballException {
}
public void event() throws BaseballException {
// Doesn't actually have to throw anything
}
public abstract void atBat() throws Strike, Foul;
public void walk() {
} // Throws no checked exceptions
}
class StormException extends Exception {
}
class RainedOut extends StormException {
}
class PopFoul extends Foul {
}
interface Storm {
public void event() throws RainedOut;
public void rainHard() throws RainedOut;
}
public class StormyInning extends Inning implements Storm {
// OK to add new exceptions for constructors, but you
// must deal with the base constructor exceptions:
public StormyInning() throws RainedOut, BaseballException {
}
public StormyInning(String s) throws Foul, BaseballException {
}
// Regular methods must conform to base class:
//! void walk() throws PopFoul {} //Compile error
// Interface CANNOT add exceptions to existing
// methods from the base class:
//! public void event() throws RainedOut {}
// If the method doesn't already exist in the
// base class, the exception is OK:
public void rainHard() throws RainedOut {
}
// You can choose to not throw any exceptions,
// even if the base version does:
public void event() {
}
// Overridden methods can throw inherited exceptions:
public void atBat() throws PopFoul {
}
public static void main(String[] args) {
try {
StormyInning si = new StormyInning();
si.atBat();
} catch (PopFoul e) {
System.err.println("Pop foul");
} catch (RainedOut e) {
System.err.println("Rained out");
} catch (BaseballException e) {
System.err.println("Generic baseball exception");
}
// Strike not thrown in derived version.
try {
// What happens if you upcast?
Inning i = new StormyInning();
i.atBat();
// You must catch the exceptions from the
// base-class version of the method:
} catch (Strike e) {
System.err.println("Strike");
} catch (Foul e) {
System.err.println("Foul");
} catch (RainedOut e) {
System.err.println("Rained out");
} catch (BaseballException e) {
System.err.println("Generic baseball exception");
}
}
} ///:~
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