java基础 异常

 异常概述：

try{ } catch{ }：

package daysreplace;
 
import com.sun.jdi.IntegerValue;
 
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Arrays;
import java.util.Calendar;
import java.util.Date;
import java.util.Scanner;
 
public class Test {
    public static void main(String[] args) throws ParseException {
        System.out.println("开始");
         try {
             a1();
         }catch (Exception e){
             System.out.println("您访问的下标越界了！");
             e.printStackTrace();//打印异常的结果
         }
        System.out.println("结束");
    }
 
    public static void a1(){
        int[] arr={22,323,22};
        System.out.println(arr[3]);
    }
}

 

Throwable的成员方法： 

 

package daysreplace;
 
import com.sun.jdi.IntegerValue;
 
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Arrays;
import java.util.Calendar;
import java.util.Date;
import java.util.Scanner;
 
public class Test {
    public static void main(String[] args) throws ParseException {
 
        try{
            System.out.println("开始");
            a1();
 
        }catch (Exception e){
            e.printStackTrace();
            System.out.println("异常内容："+e.getMessage());//e.get
            System.out.println("异常内容："+e.toString());
            System.out.println("转换类型错误啦！");
        }
        System.out.println("结束");
 
 
    }
    public static void a1(){
 
          String str="1,2,34,4";
        int i = Integer.parseInt(str);
        System.out.println(i);
 
//        int[] arr={22,323,22};
//        System.out.println(arr[3]);
    }
 
 
}

编译时异常和运行时异常的区别： 

 

 

throws 关键字：

 

自定义异常，继承Exception即可：

LoginException.java:

package dateStudy;
 
public class LoginException extends Exception{
    //alt+insert 生成一个有参构造
    public LoginException(String message) {
        super(message);
    }
 
}

 LoginTest.java:

package dateStudy;
 
import java.util.Locale;
import java.util.Scanner;
 
public class LoginTest {
    public static void main(String[] args) throws LoginException {
 
        System.out.println("开始");
 
        System.out.println("请输入账号");
        Scanner sc = new Scanner(System.in);
        String s = sc.nextLine();
        System.out.println("请输入密码");
        Scanner sc1 = new Scanner(System.in);
        String s1 = sc1.nextLine();
 
        try {
            login(s,s1);
      } catch (LoginException e) {
            e.printStackTrace();
        }
        System.out.println("结束");
    }
 
    public static void login(String userName, String pwd) throws LoginException {
        if (!("wwx".equals(userName)&&"123456".equals(pwd))) {
            throw new LoginException("用户输入的账号和密码不正确");
        }
        System.out.println("输入正确，登陆成功");
 
    }
 
}