抛出异常的时候,异常处理系统会安装代码书写顺序找出"最近"的处理程序. 找到匹配的程序后,它就认为异常将得到清理,然后就不再继续查找.
查找的时候并不要求抛出的异常同处理程序的异常完全匹配.派生类的对象也可以配备其基类的处理程序
package exceptions;
//: exceptions/Human.java
// Catching exception hierarchies. class Annoyance extends Exception {}
class Sneeze extends Annoyance {} public class Human {
public static void main(String[] args) {
// Catch the exact type:
try {
throw new Sneeze();
} catch(Sneeze s) {
System.out.println("Caught Sneeze");
} catch(Annoyance a) {
System.out.println("Caught Annoyance");
}
// Catch the base type:
try {
throw new Sneeze();
} catch(Annoyance a) {
System.out.println("Caught Annoyance");
}
}
} /* Output:
Caught Sneeze
Caught Annoyance
*///:~
换句话说,捕获基类的异常,就可以匹配所有派生类的异常
try {
throw new Sneeze();
} catch(Annoyance a) {
} catch(Sneeze s) { //这句编译器会报错,异常已由前面catch子句处理
}