20191102Java课堂记录

1.

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("111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");
    }
  }
}

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

3.

public class CatchWho2 {
    public static void main(String[] args) {
        try {
                try {
                    throw new ArrayIndexOutOfBoundsException();
                }
                catch(ArithmeticException e) {
                    System.out.println( "11ArrayIndexOutOfBoundsException" + "/内层try-catch");
                }
            throw new ArithmeticException();
        }
        catch(ArithmeticException e) {
            System.out.println("22发生ArithmeticException");
        }
        catch(ArrayIndexOutOfBoundsException e) {
            System.err.println( "33ArrayIndexOutOfBoundsException" + "/外层try-catch"); 

        }
    }
}

运行结果：

33ArrayIndexOutOfBoundsException/外层try-catch

4.

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");

        }

    }

}

结论：

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。

5.

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");

        }

    }

}

结论：

finally不一定会执行