32.Java基础_异常

JVM虚拟机默认异常处理机制

Java异常处理：

1.try...catch...

2.throw

1.try...catch...

public class test{
    public static void main(String[] args) {
        System.out.println("开始");
        method();
        System.out.println("结束");
    }
    public static void method(){
        int[] arr={1,2,3};
        try {
            System.out.println(arr[3]); //访问超出索引
        }
        catch (ArrayIndexOutOfBoundsException e){
            e.printStackTrace();
        }
    }
}
/*
开始
java.lang.ArrayIndexOutOfBoundsException: Index 3 out of bounds for length 3
    at pack2.test.method(test.java:13)
    at pack2.test.main(test.java:7)
结束
 */

Exception异常类常用方法

编译时异常和运行时异常

2.throws

throws将异常抛出去，让try_catch_来处理

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
public class test{
    public static void main(String[] args) {
        System.out.println("开始");
        try {
            method();
        }
        catch (ArrayIndexOutOfBoundsException e){
            e.printStackTrace();
        }
        try {
            method2();
        }
        catch (ParseException e){
            e.printStackTrace();
        }
        System.out.println("结束");
    }
    //编译时异常,不加throws ParseException不能编译
    public static void method2() throws ParseException {
        String s="2048-08-09";
        SimpleDateFormat sdf=new SimpleDateFormat("yyy-MM-dd");
        Date d=sdf.parse(s);
        System.out.println(d);
    }
    //运行时异常，不加throws ArrayIndexOutOfBoundsException可以编译
    public static void method() throws ArrayIndexOutOfBoundsException{
        int[] arr={1,2,3};
        System.out.println(arr[3]);
    }
}
/*
开始
java.lang.ArrayIndexOutOfBoundsException: Index 3 out of bounds for length 3
    at pack2.test.method(test.java:36)
    at pack2.test.main(test.java:13)
Sun Aug 09 00:00:00 CST 2048
结束
 */

自定义异常

public class ScoreException extends Exception{
    public ScoreException() {}
    public ScoreException(String message) {
        super(message);
    }
}

public class Teacher{
    public void checkScore(int score) throws ScoreException{
        if(score<0||score>100){
            throw new ScoreException(); //抛出异常对象
        }
        else {
            System.out.println("分数正常");
        }
    }
}

import java.util.Scanner;
public class test{
    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();
        }
    }
}