Java语言之异常处理类

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package step1;

import java.util.Scanner;

public class ThrowException {
	public static void function(String id) {  //利用throws关键字声明该方法可能出现异常IllegalArgumentException
		/********** Begin *********/
		if (id.length() == 7) {
			//输出ID合法时的语句
System.out.print("ID格式正确："+id);
		}
	    else {
			//利用throw关键字抛出异常IllegalArgumentException
throw new IllegalArgumentException();
		}
		/********** End *********/
	}

	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		String id=sc.nextLine();
		try {
	        function(id);
	    }
	    catch (IllegalArgumentException e) {           //可以看成一个flag？  
			/********** Begin *********/
			//输出ID不合法时的语句
System.out.print("ID长度应为7");


			/********** End *********/
	    }
	}
}

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package step2;
import java.io.*;

public class CatchException {
    public static void main(String[] args) {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String str;
        int letter=0,space=0,number=0,other=0;
        /********** Begin *********/
        //补全try/catch块，异常类型为IOException
        try
        {
        	str=reader.readLine();//必须放在try里面，因为要有一个返回值来判断是否抛出
            char str1[]=str.toCharArray();
        	for (int i=0;i<str1.length;i ++)
        	{
        		if (Character.isLetter(str1[i]))
        		{
        			letter++;
        		}
        		else if (Character.isSpaceChar(str1[i]))
        		{
        			space++;
        		}
        		else if (Character.isDigit(str1[i]))
        		{
        			number++;
        		}
        		else other++;
        	}
        	System.out.println("letter="+letter +",space="+ space + ",number=" + number+",other="+other);
        	
        }catch(IOException e){
        	e.printStackTrace();
          }
        /********** End *********/
    }
}

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package step3;

import java.util.Scanner;

class MyException extends Exception {
    public MyException(String m) {
        super(m);
    }
}
public class MyExceptionTest {
    public static void main(String[] args) {
        try {
            Scanner scanner = new Scanner(System.in);
            int num = scanner.nextInt();
            /********** Begin *********/
            if(num<0)
            {
                throw new MyException("Number cannot be negative!");
            }
            else 
            System.out.print("The number you entered is: "+num);

            /********** End *********/
        }
        catch(MyException e) {
            System.out.print(e);
        }
    }
}