Java foundation abnormal Review _day12_

abnormal

1 Overview

• An exception is that the program appeared in unusual circumstances

2. Architecture

3. JVM the default way to handle exceptions

• The output unusual name, location and cause of the error exception occurs in the console
• Program to stop execution

4. try-catch manner exception

① Definition Format

try {
	可能出现异常的代码;
} catch(异常类名 变量名) {
	异常的处理代码;
}

② execution process

• Program starts executing code from a try inside
• If an exception occurs, it will jump to the corresponding catch inside to perform
• After execution is completed, the program can continue down

Example ③

public class ExceptionDemo01 {
    public static void main(String[] args) {
        System.out.println("开始"); // 输出开始
        method();// 方法中存在异常, 但并不会终止程序
        System.out.println("结束"); // 输出结束
    }

    public static void method() {
        try {
            int[] arr = {1, 2, 3};
            System.out.println(arr[3]); // 索引越界异常,程序跳转到catch中
            System.out.println("这里能够访问到吗");// 该条代码不会执行
        } catch (ArrayIndexOutOfBoundsException e) {
            e.printStackTrace(); // 输出异常信息
        }
    }
}

5. throws exception manner

① Definition Format

public void 方法() throws 异常类名 {
    
}

② example

public class ExceptionDemo {
    public static void main(String[] args) {
        System.out.println("开始");
//        method();
        try {
            method2();
        }catch (ParseException e) {
            e.printStackTrace();
        }
        System.out.println("结束");
    }

    //编译时异常
    public static void method2() throws ParseException {
        String s = "2048-08-09";
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        Date d = sdf.parse(s);
        System.out.println(d);
    }

    //运行时异常
    public static void method() throws ArrayIndexOutOfBoundsException {
        int[] arr = {1, 2, 3};
        System.out.println(arr[3]);
    }
}

The difference between abnormal and abnormal operation 6. compile time

① compile-time anomaly

• Exception class and its subclasses are
• Must display processing, otherwise the program will error, not compile

② runtime exception

• It is RuntimeException and its subclasses
• Without displaying processing, can also be treated as an exception and compile-time

7. custom exception

// 自定义异常类
class ScoreException extends Exception {

    public ScoreException() {}

    public ScoreException(String message) {
        super(message);
    }
}
// 老师类
class Teacher {
    public void checkScore(int score) throws ScoreException {
        if(score<0 || score>100) {
//            throw new ScoreException();
            throw new ScoreException("你给的分数有误，分数应该在0-100之间");
        } else {
            System.out.println("成绩正常");
        }
    }
}
// 测试类
public class Demo {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入分数：");

        int score = sc.nextInt();

        Teacher t = new Teacher();
        try {
            t.checkScore(score);
        } catch (ScoreException e) {
            e.printStackTrace();
        }
    }
}