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JAVA动手动脑异常处理
1>请阅读并运行AboutException.java示例,然后通过后面的几页PPT了解Java中实现异常处理的基础知识。
import javax.swing.*;
class AboutException {
public static void main(String[] a)
{
float i=1, j=0, k;
k=i/j;
System.out.println(k);
try
{
k = i/j; // Causes division-by-zero exception
//throw new Exception("Hello.Exception!"); }
catch ( ArithmeticException e)
{
System.out.println("被0除. "+ e.getMessage());
}
catch (Exception e)
{
if (e instanceof ArithmeticException)
System.out.println("被0除");
else
{
System.out.println(e.getMessage());
}
}
finally
{
JOptionPane.showConfirmDialog(null,"OK");
}
}
}
异常处理:Java中异常捕获语句
try{用于监控可能发生错误的语句}
catch(异常类型 异常对象引用)
{ 用于捕获并处理异常的代码 }
finally
{ //用于“善后” 的代码 }
不管是否有异常发生,finally语句块中的语句始终保证被执行。
2>阅读以下代码(CatchWho.java),写出程序运行结果:
public class CatchWho {
public static void main(String[] args) {
try {
try {
throw new ArrayIndexOutOfBoundsException();
}
catch(ArrayIndexOutOfBoundsException e) {
System.out.println( "ArrayIndexOutOfBoundsException" + "/内层try-catch");
}
throw new ArithmeticException();
}
catch(ArithmeticException e) {
System.out.println("发生ArithmeticException");
}
catch(ArrayIndexOutOfBoundsException e) {
System.out.println( "ArrayIndexOutOfBoundsException" + "/外层try-catch");
}
}
}
运行结果:
ArrayIndexOutOfBoundsException/内层try-catch
发生ArithmeticException
结果分析:当内层捕获异常并处理后,外层则不再捕获该异常。
3>写出CatchWho2.java程序运行的结果
public class CatchWho2 {
public static void main(String[] args) {
try {
try {
throw new ArrayIndexOutOfBoundsException();
}
catch(ArithmeticException e) {
System.out.println( "ArrayIndexOutOfBoundsException" + "/内层try-catch");
}
throw new ArithmeticException();
}
catch(ArithmeticException e) {
System.out.println("发生ArithmeticException");
}
catch(ArrayIndexOutOfBoundsException e) {
System.out.println( "ArrayIndexOutOfBoundsException" + "/外层try-catch");
}
}
}
运行结果:
ArrayIndexOutOfBoundsException/外层try-catch
结果分析:当异常未被处理时无法接受新的异常。
4>请先阅读 EmbedFinally.java示例,再运行它,观察其输出并进行总结。
public class EmbededFinally {
public static void main(String args[]) {
int result;
try {
System.out.println("in Level 1");
try {
System.out.println("in Level 2");
//result=100/0; //Level 2
try {
System.out.println("in Level 3");
result=100/0; //Level 3 }
catch (Exception e) {
System.out.println("Level 3:" + e.getClass().toString());
}
finally {
System.out.println("In Level 3 finally");
}
// result=100/0; //Level 2 }
catch (Exception e) {
System.out.println("Level 2:" + e.getClass().toString());
}
finally {
System.out.println("In Level 2 finally");
}
// result = 100 / 0; //level 1 }
catch (Exception e) {
System.out.println("Level 1:" + e.getClass().toString());
}
finally {
System.out.println("In Level 1 finally");
}
}
}
运行结果:
结果分析:当外层异常未被处理时,内层异常不会被处理并且finally也不会执行,当有多层嵌套的finally语句时,异常在不同层次不同位置抛出时,也会导致不同的finally语句块执行顺序。
5>finally语句块一定会执行吗?
请通过 SystemExitAndFinally.java示例程序回答上述问题
public class SystemExitAndFinally {
public static void main(String[] args)
{
try{
System.out.println("in main");
throw new Exception("Exception is thrown in main");
//System.exit(0); }
catch(Exception e)
{
System.out.println(e.getMessage());
System.exit(0);
}
finally
{
System.out.println("in finally");
}
}
}
运行结果:
运行结果:首先只有与finally对应的try语句得到执行的情况下finally语句才会执行,但如果finally语句之前出现例如System.exit(0) 等使Java虚拟机停止运行的语句时finally语句也不会被执行。
6>编写一个程序,此程序在运行时要求用户输入一个 整数,代表某门课的考试成绩,程序接着给出“不及格”、“及格”、“中”、“良”、“优”的结论。
import java.util.Scanner;class MyException extends Exception
{
MyException(String str)
{
super(str);
}
}class GradeTest{
private double grade;
public void InputGrade(String s)
{
boolean flag = true;
try
{
for(int i = 0;i<s.length();i++)
{
if((s.charAt(i) < ‘0‘ || s.charAt(i) > ‘9‘)&& s.charAt(i) != ‘.‘)
flag = false;
}
if(!flag)
{
throw new MyException("请输入数字!");
}
try{
grade = Double.parseDouble(s);
if(grade < 0.0 || grade > 100.0)
{
throw new MyException("请输入0.0到100.0的数据!");
}
if(grade < 60.0)
System.out.println("不及格");
else if(grade <70.0)
System.out.println("及格");
else if(grade < 80.0)
System.out.println("中");
else if(grade < 90.0)
System.out.println("良");
else
System.out.println("优");
}
catch(MyException e)
{
System.out.println(e.getMessage());
}
}
catch(MyException e)
{
System.out.println(e.getMessage());
}
}
}public class Grade {
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner in = new Scanner(System.in);
GradeTest G = new GradeTest();
System.out.println("请输入成绩:");
String str = in.nextLine();
G.InputGrade(str);
in.close();
}
}
运行结果:
JAVA动手动脑异常处理