动手动脑集合五

题目一：请阅读并运行AboutException.java示例

AboutException.java

import javax.swing.JOptionPane;

public class AboutException {
    public static void main(String[] args) {
        int i=1,j=0,k;
        k=i/j;
        
        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：

 

题目二：阅读以下代码（CatchWho.java）

CatchWho.java

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"); 
        } 
    } 
}

执行结果：

 

CatchWho2.java

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"); 
        } 
    } 
}

执行结果：

 

题目三：请先阅读 EmbedFinally.java示例，再运行它，观察其输出并进行总结。

EmbedFinally.java

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 
                }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");
        }
    }
}

执行结果为：

 

 将result的表达式换在第二个try里面，其执行代码为：

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 
                }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");
        }
    }
}

执行结果为：

 

  将result的表达式换在第一个try里面，其执行代码为：

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 
                }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");
        }
    }
}

执行结果为：

总结：

在try..catch...finally语句中，try里面的是率先执行的，若是try内的语句有错误，catch中的语句才会执行，若是无错误，便会执行finally内的语句。

 

题目四：辨析：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

SystemExitAndFinally.java

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");
        }
    }
}

执行结果为：

 

 若程序改为：

 

 则会出现以下错误：

 结论：finally代码块不一定会被执行