java基础-异常Exception-day10

目录

• 1. 练习
• 2. 异常三联 try-catch-finally
• 3.异常的分类
• 3. 子类throws的异常 小于等于父类的异常
• 4.自定义异常

1. 练习

package com.msb01;

import java.util.Scanner;

/**
 * @Auther: jack.chen
 * @Date: 2023/9/17 - 09 - 17 - 10:58
 * @Description: com.msb01
 * @version: 1.0
 */
public class Test {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入第一个数：");
        int num1 = sc.nextInt();

        System.out.println("请输入第二个数：");
        int num2 = sc.nextInt();

        System.out.println(num1/num2);
    }
}

通过 if-else堵住异常 可读性 差

2. 异常三联 try-catch-finally

package com.msb01;

import java.util.Scanner;

/**
 * @Auther: jack.chen
 * @Date: 2023/9/17 - 09 - 17 - 10:58
 * @Description: com.msb01
 * @version: 1.0
 */
public class Test {
    public static void main(String[] args) {
        try {
            Scanner sc = new Scanner(System.in);
            System.out.println("请输入第一个数：");
            int num1 = sc.nextInt();

            System.out.println("请输入第二个数：");
            int num2 = sc.nextInt();

            System.out.println(num1/num2);
        } catch (Exception e) {
            e.printStackTrace();
        }

        System.out.println(1111);
        System.out.println(222);
        System.out.println(333);
    }
}

异常被打印 后续代码正常执行

如果catch中异常的类型不匹配 不会走catch的逻辑 相当于 没捕获

异常捕获后如何处理

1. 不处理
2. 自定义输出
3. 打印异常
4. 抛出异常

![](https://img2023.cnblogs.com/blog/1422290/202309/1422290-20230917110918461-828857373.png)

什么情况下 try-catch 后面的逻辑(谢谢使用计算器)不会执行

1. throw抛出异常
2. catch 没有捕获住异常
3. try中遇到return 方法里面将返回值返回调用方

怎样才能 无论如何都执行try-catch 后面的逻辑

将逻辑放入 finally

reuturn与finally的先后顺序

先finally后return （记忆方法 f排序在r的前面）

哪些逻辑会放入finally

关系数据源 关闭io 关闭socket

有一句代码很厉害可以不让finally里面的逻辑执行

System.exit(0)； jvm虚拟机退出

package com.msb01;

import java.util.Scanner;

/**
 * @Auther: jack.chen
 * @Date: 2023/9/17 - 09 - 17 - 10:58
 * @Description: com.msb01
 * @version: 1.0
 */
public class Test {
    public static void main(String[] args) {
        try {
            Scanner sc = new Scanner(System.in);
            System.out.println("请输入第一个数：");
            int num1 = sc.nextInt();

            System.out.println("请输入第二个数：");
            int num2 = sc.nextInt();

            System.out.println(num1/num2);

//            System.exit(0);
            return;
        } catch (Exception e) {
            System.out.println("对不起输出有误 无法计算");

            System.out.println(e.toString());
            System.out.println(e.getMessage());
            e.printStackTrace();

//            throw e;
        } finally {
            System.out.println("谢谢使用计算器");
        }
    }
}

并列符| 连接多个异常

package com.msb01;

import java.util.InputMismatchException;
import java.util.Scanner;

/**
 * @Auther: jack.chen
 * @Date: 2023/9/17 - 09 - 17 - 10:58
 * @Description: com.msb01
 * @version: 1.0
 */
public class Test {
    public static void main(String[] args) {
        try {
            Scanner sc = new Scanner(System.in);
            System.out.println("请输入第一个数：");
            int num1 = sc.nextInt();

            System.out.println("请输入第二个数：");
            int num2 = sc.nextInt();

            System.out.println(num1/num2);

//            System.exit(0);
            return;
        } catch (ArithmeticException |InputMismatchException |Exception) {
            System.out.println("对不起输出有误 无法计算");
        } finally {
            System.out.println("谢谢使用计算器");
        }
    }
}

3.异常的分类

检查异常：防范于未然 写代码的时候就要对代码的异常进行处理

运行异常：写代码的会后不用特意对异常进行处理 运行过程中没法执行 才会抛出异常

package com.msb01;

/**
 * @Auther: jack.chen
 * @Date: 2023/9/17 - 09 - 17 - 11:38
 * @Description: com.msb01
 * @version: 1.0
 */
public class TestException01 {

    public static void main(String[] args) {
        int[] a1 = {1, 2,3};
        System.out.println(a1[10]);
    }
}

public class TestException01 {

    public static void main(String[] args) {
        int[] a1 = {1, 2,3};
//        System.out.println(a1[10]);
        int[] a2 = null;
        System.out.println(a2.length);
    }
}

package com.msb01;

/**
 * @Auther: jack.chen
 * @Date: 2023/9/17 - 09 - 17 - 11:41
 * @Description: com.msb01
 * @version: 1.0
 */
public class TestException02 {

    public static void main(String[] args) {
        Class.forName("com.msb01.Test").newInstance();
    }
}
![](https://img2023.cnblogs.com/blog/1422290/202309/1422290-20230917114307186-307719948.png)

package com.msb01;

/**
 * @Auther: jack.chen
 * @Date: 2023/9/17 - 09 - 17 - 11:41
 * @Description: com.msb01
 * @version: 1.0
 */
public class TestException02 {

    public static void main(String[] args) {
        try {
            Class.forName("com.msb01.Test").newInstance();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

package com.msb01;

/**
 * @Auther: jack.chen
 * @Date: 2023/9/17 - 09 - 17 - 11:41
 * @Description: com.msb01
 * @version: 1.0
 */
public class TestException02 {

    public static void main(String[] args) {
        try {
            Class.forName("com.msb01.Test").newInstance();
        } catch (InstantiationException|IllegalAccessException|ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

alt+enter快捷键

提示两种处理方式 一个是 throws 一个是 try/catch

package com.msb01;

/**
 * @Auther: jack.chen
 * @Date: 2023/9/17 - 09 - 17 - 11:41
 * @Description: com.msb01
 * @version: 1.0
 */
public class TestException02 {

    public static void main(String[] args) throws ClassNotFoundException, IllegalAccessException, InstantiationException {
        Class.forName("com.msb01.Test").newInstance();

    }
}

3. 子类throws的异常 小于等于父类的异常

package com.msb01;

/**
 * @Auther: jack.chen
 * @Date: 2023/9/17 - 09 - 17 - 11:47
 * @Description: com.msb01
 * @version: 1.0
 */
public class Person {

    public void eat() throws RuntimeException{
        System.out.println("eat");

    }
}

4.自定义异常

package com.msb01;

/**
 * @Auther: jack.chen
 * @Date: 2023/9/17 - 09 - 17 - 11:51
 * @Description: com.msb01
 * @version: 1.0
 */
public class MyException extends RuntimeException {
    static final long serialVersionUID = -70348971907L;

    public MyException() {
    }

    public MyException(String message) {
        super(message);
    }
}

检查异常 需要使用try-catch捕获 或者throws