黑马程序员——面向对象-异常

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异常处理的捕捉模式：

class FuShuIndexException extends Exception {FuShuIndexException() {}FuShuIndexException(String msg) {super(msg);}}class Demo {public int method(int[] arr, int index) throws Exception// throws// NullPointerException,FuShuIndexException{if (arr == null)throw new NullPointerException("没有任何数组实体");if (index < 0)throw new FuShuIndexException();return arr[index];}}class ExceptionDemo4 {public static void main(String[] args) throws Exception {int[] arr = new int[3];Demo d = new Demo();try {int num = d.method(null, -1);System.out.println("num=" + num);}catch (NullPointerException e) {System.out.println(e.toString());} catch (FuShuIndexException e) {System.out.println("message:" + e.getMessage());System.out.println("string:" + e.toString());e.printStackTrace();// jvm默认的异常处理机制就是调用异常对象的这个方法。System.out.println("负数角标异常!!!!");}/* * catch(Exception e)//多catch父类的catch放在最下面。 { *  * } */System.out.println("over");}}

异常转化：

/* 毕老师用电脑上课。 问题领域中涉及两个对象。 毕老师，电脑。 分析其中的问题。 比如电脑蓝屏啦。冒烟啦。 */class LanPingException extends Exception {LanPingException(String msg) {super(msg);}}class MaoYanException extends Exception {MaoYanException(String msg) {super(msg);}}class NoPlanException extends Exception {NoPlanException(String msg) {super(msg);}}class Computer {private int state = 2;public void run() throws LanPingException, MaoYanException {if (state == 1)throw new LanPingException("电脑蓝屏啦！！");if (state == 2)throw new MaoYanException("电脑冒烟啦！！");System.out.println("电脑运行");}public void reset() {state = 0;System.out.println("电脑重启");}}class Teacher {private String name;private Computer comp;Teacher(String name) {this.name = name;comp = new Computer();}public void prelect() throws NoPlanException {try {comp.run();System.out.println(name + "讲课");} catch (LanPingException e) {System.out.println(e.toString());comp.reset();prelect();} catch (MaoYanException e) {System.out.println(e.toString());test();// 可以对电脑进行维修。// throw e;throw new NoPlanException("课时进度无法完成，原因：" + e.getMessage());}}public void test() {System.out.println("大家练习");}}class ExceptionTest {public static void main(String[] args) {Teacher t = new Teacher("毕老师");try {t.prelect();} catch (NoPlanException e) {System.out.println(e.toString() + "......");System.out.println("换人");}}}

异常这部分是很重要的，与之重要性相同的是学习难度也挺大。主要在于理解抛出和捕捉两种模式。

我是这样理解的：抛出就是在程序本身解决不了的要抛出给用户看到。而捕捉的异常一般是可以在程序内部进行调整的，当然也可以抛出。有理解不到位的地方，大家多指点。

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