1.
import javax.swing.*; class AboutException { public static void main(String[] a) { double i=1, j=0, k; k=i/j; System.out.print(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"); } } }
运行结果:
Hello.Exception!
总结:Java 中所有可捕获的异常都派生自 Exception 类。
把可能会发生错误的代码放进try语句块中。 当程序检测到出现了一个错误时会抛出一个异常对象。
异常处理代码会捕获并处理这个错误。 catch语句块中的代码用于处理错误。
当异常发生时,程序控制流程由try语句块跳转到catch语句块。
不管是否有异常发生,finally语句块中的语句始终保证被执行。
如果没有提供合适的异常处理代码,JVM将会结束掉整个应用程序。
2,
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
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
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"); } } 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:
in Level 1
in Level 2
in Level 3
Level 3:class java.lang.ArithmeticException
In Level 3 finally
In Level 2 finally
In Level 1 finally
改变 result=100/0; 位置
运行结果:
in Level 1
in Level 2
in Level 3
In Level 3 finally
Level 2:class java.lang.ArithmeticException
In Level 2 finally
In Level 1 finally
总结:
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语句块执行顺序。
当程序中出现异常时,JVM会依据方法调用顺序依次查找有关的错误处理程序。
3.
public class SystemExitAndFinally { public static void main(String[] args) { try{ System.out.println("in main"); throw new Exception("Exception is thrown in main"); } catch(Exception e) { System.out.println(e.getMessage());//getmessage()输出错误信息,可直接用对象调用。 //System.exit(0); } finally { System.out.println("in finally"); } } }
运行结果:
in main
Exception is thrown in main
总结:不管是否有异常发生,finally语句块中的语句始终保证被执行。特殊情况,在catch中有“System.exit(0);”执行此语句后,就已经结束程序,故不会运行finally语句。