异常(exception):发生在程序执行期间,表明出现了一个非法运行的情况。许多JDK中的方法在检测到非法情况时,都会抛出一个异常对象。例如:数组越界和被0除。
代码验证:
package test; import javax.swing.*; class AboutException { public static void main(String[] a) { int i=1, j=0, 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"); } } }
输出结果:
当java程序中出现多try catch的情况时,一定要注意程序执行的先后顺序。
多try catch的java异常处理代码一
package test; 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"); } } }
程序运行结果:
多try catch的java异常处理代码二
package test; 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"); } } }
程序运行结果:
当有多个try catch finally嵌套 时,要特别注意finally的执行时机。特别注意:当有多层嵌套的finally时,异常在不同的层次抛出,在不同的位置抛出,可能会导致不同的finally语句的执行顺序。再者,我们一般认为finally语句中的句子一定会被执行,这里的一定是相对而言的,并不是绝对的。例如以下程序代码的运行:
package test; 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:
在这段java代码中finally语句块并没有执行。
通过过异常的学习,自己尝试了自定义了一个异常类来处理异常,源码如下:
package classtest; import java.util.Scanner; class Myexception extends Exception { public Myexception(String message) { super(message); } } public class Mytest { public static void main(String[] args) throws Exception{ // TODO Auto-generated method stub try{ function(); } catch (Exception e) { System.out.println(e.getMessage()); System.out.println("main()函数运行时出现异常"); } finally { System.out.println("main()函数运行完毕"); } } public static int judge(String str) { int c = 0; String regex = "[0-9]+"; String regex1="[-][0-9]+"; boolean d = str.matches(regex); boolean e = str.matches(regex1); if (d == false) { c = 1; if (e == true) { c = 0; } } return c; } public static void function() { try { System.out.println("请输入一个正整数:"); Scanner input = new Scanner(System.in); String a = input.next(); int temp = judge(a); if (temp == 1) { throw new Myexception("不能输入非法字符"); } else { int num = Integer.parseInt(a); if (num < 0) throw new Myexception("输入不能为负数"); else if (num == 0) { throw new Myexception("正整数不包括0"); } } } catch (Myexception f) { System.out.println(f.getMessage()); } catch (Exception e) { System.out.println(e.getMessage()); System.out.println("function()函数运行时出现异常"); } finally { System.out.println("function()函数已运行完毕,请指示下一步动作"); } } }
原文地址:https://www.cnblogs.com/weixiao1717/p/11780111.html
时间: 2024-10-13 02:02:39