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：

类型不匹配：不能从Mammal转换为Dog

类型不匹配：不能从Cat转换为Dog

二.CatchWho.java

三.CatchWho2.java

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

import java.util.Scanner;
public class Scorelevel {
 public static void main(String[] args) {
  System.out.println("请输入学生的成绩：");
  Scanner sc = new Scanner(System.in);
  String ss = sc.next(); //将数据以String类型的方式读入
  if(isInt(ss)==false) {
   System.exit(0);
  }
  else {
   int score = Integer.valueOf(ss);
   if(score<0||score>100) {
    System.out.println("您输入的数据不合法，请重新输入：");
   }
   else if(score>=0&&score<60) {
    System.out.println("成绩等级为不及格");
   }
   else if(score>=60&&score<70) {
    System.out.println("成绩等级为及格");
   }
   else if(score>=70&&score<80) {
    System.out.println("成绩等级为中等");
   }
   else if(score>=80&&score<90) {
    System.out.println("成绩等级为良好");
   }
   else {
    System.out.println("成绩等级为优秀");
   }
   sc.close();
  }
 }
 public static boolean isInt(String ss) {
  Integer it = null;
  try {
   it = Integer.valueOf(ss);
  } catch (NumberFormatException e) {
   System.out.println("您输入的数据不合法，请重新输入：");
   return false;
  }
  return true;
 }
}