java中异常的限制

子类在覆盖父类方法时，父类的方法如果抛出了异常，那么子类的方法只能抛出父类的异常或者该异常的
子类。
如果父类抛出多个异常，那么子类只能抛出父类异常的子集。
简单说：子类覆盖父类只能抛出父类的异常或者子类的子集

package example;
class OneException extends Exception{}
class TwoException extends Exception{}
class a{
    public a() throws OneException{

    }
    public void event() throws TwoException{}
}

public class Test extends a{

    public Test() throws TwoException, OneException {
        super();
    }
    //public void event()throws OneException {} //编译失败
    //public void event()throws OneException,TwoException {}//编译失败
    public void event()throws TwoException {}
}

还可以看出以上说法不适用与构造器方法，异常限制对构造器不起作用，子类构造器可以抛出任何异常，而不必理会基类构造器所抛出的异常，然而

基类构造器必须以这样那样的1方式的被调用，派生类构造器的异常说明必须包含基类构造器的异常说明。

接口对异常限制

package example;
class OneException extends Exception{}
class TwoException extends Exception{}
class ThreeException extends Exception{}
class a{
    public a() throws OneException{

    }
    public void event() throws TwoException{}
}
interface B{
    public void event()throws ThreeException ;
    public void show() throws ThreeException;
}

public class Test extends a implements B{

    public Test() throws TwoException, OneException {
        super();
    }

    //public void event()throws ThreeException {} //编译失败
    //public void event()throws TwoException,ThreeException {} //编译失败
    //public void event()throws TwoException {}//编译失败
    public void event(){
    }
    public void show() throws ThreeException  {
    }

}

子类方法抛出的异常可以是基类方法异常的子类

package example;
class OneException extends Exception{}
class TwoException extends Exception{}
class ThreeException extends TwoException{}
class a{
    public a() throws OneException{

    }
    public void event() throws TwoException{}
}

public class Test extends a {

    public Test() throws TwoException, OneException {
        super();
    }

    public void event() throws ThreeException{
    }

}