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

import java.util.Scanner;

public class ScoreRange {
    public static void main(String[] args) {
        System.out.println("请输入成绩");
        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("您输入的数据非法，请重新输入");
            }
            else if(score>=0&&score<60) {
                System.out.println("不及格");
            }
            else if(score>=60&&score<70) {
                System.out.println("及格");
            }
            else if(score>=70&&score<80) {
                System.out.println("中等");
            }
            else if(score>=80&&score<90) {
                System.out.println("良好");
            }
            else {
                System.out.println("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;
    }
}

截图：