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();
         }
     }
 }