5. 什么是异常
定义：在程序的运行过程中所发生的异常事件，它中断指令的正常执行。 Java中提供了一种独特的异常处理机制。
没有处理错误的程序 3. 以常规方法处理错误 8.1 异常的概念 read-file {
openTheFile;
determine its size;
allocate that much memory;
read the file into memory;
statement；
closeTheFile;
} openFiles;
if (theFilesOpen) {
determine the lenth of the file;
if (gotTheFileLength){
allocate that much memory;
if (gotEnoughMemory) {
read the file into memory;
if (readSuccess){
statement;
if(closeTheFile) closeFile;
else errorCode=-1;
}else errorCode=-2;
}else errorCode=-3;
}else errorCode=-4;
}else errorCode=-5; 缺点
16. 例子3，处理replaceValue引发的异常8.6 try、catch和finally Object value = new Integer(8);
try{
attributedObj.replaceValue("Age", value);
}catch (NoSuchAttributeException e) {
// shouldn't happen, but recover if it does
Attr attr = new Attr(e.attrName, value);
attributeObj.add(attr);
}
17. 捕获异常对象的顺序和catch语句的顺序有关，当捕获到一个异常对象时，剩下的catch语句就不再进行匹配。因此，在安排catch语句的顺序时，首先应该捕获最特殊的异常对象，然后再逐渐一般化。即先安排子类，再安排父类。
若引发的异常与catch中的异常类型或超类类型都不匹配，该异常将被转送到调用这个方法的代码。8.6 try、catch和finally class SuperException extends Exception { }
class SubException extends SuperException { }
class BadCatch {
public void goodTry() {
/* This is an INVALID catch ordering */
try {
throw new SubException();
} catch (SuperException superRef) {
// Catches both SuperException and SubException
} catch (SubException subRef) {
// This would never be reached
}
}
}
