课后作业

一.下列语句哪一个将引起编译错误?为什么?哪一个会引起运行时错误?为什么?

m=d;

d=m;

d=(Dog)m;

d=c;

c=(Cat)m;

d=m;和d=c;引起编译错误；

原因：

二.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"); 
        } 
    } 
}

三.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"); 
        } 
    } 
}

结果：ArrayIndexOutOfBoundsException/外层try-catch

四.EmbededFinally.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 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

五.课后作业2

package score;
import java.io.BufferedReader;//
import java.io.InputStreamReader;//
public class Score {
public static void main(String[] args){
    int num=110 ;
    String str ;
    BufferedReader brd=new BufferedReader(new InputStreamReader(System.in)) ;//构造方法
    while(true)
    {
        System.out.print("请输入数字:") ;
        try
        {
            str=brd.readLine() ;
            System.out.print("输入为："+str);
            num=Integer.parseInt(str) ;
            
        }
        catch(Exception e)
        {
            System.out.println("	对不起，只能输入整数，请重新输入。") ;
        }
        
        
        if(num>100||num<0)
        {
            
            System.out.println("对不起，只能输入1-100整数，请重新输入。") ;
        }
        else break;
    }
    if(num<60)
        System.out.println("你输入的整数是: "+num+"成绩为：不及格") ;
    else if(num<70)
        System.out.println("你输入的整数是: "+num+"成绩为：及格") ;
    else if(num<80)
        System.out.println("你输入的整数是: "+num+"成绩为：良") ;
    else if(num<90)
        System.out.println("你输入的整数是: "+num+"成绩为：中") ;
    else System.out.println("你输入的整数是: "+num+"成绩为：优") ;
    
}
}