异常概念 异常体系

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异常的产生过程解析

异常的产生过程解析

throw关键字

throw关键字

Objects非空判断

 public static void main(String[] args) {
        test(null);
    }
    public static  void test(Object object){
     Objects.requireNonNull(object, "object 方法为null");
     
    }

Objects非空判断

throws关键字

 public static void main(String[] args) throws FileNotFoundException {
        test("c:\\a.txt111");
    }
    public static  void test(String filrName) throws FileNotFoundException{
     if (!filrName.equals("c:\\a.txt")){
         throw new FileNotFoundException("文件没找到");
     }

    }

throws关键字

try...catch关键字

  public static void main(String[] args)  {
        try {
            test("c:\\a.txt111");
        } catch (FileNotFoundException e) {
            e.printStackTrace();
            System.out.println("出现异常");
        }
    }
    public static  void test(String filrName) throws FileNotFoundException{
     if (!filrName.equals("c:\\a.txt")){
         throw new FileNotFoundException("文件没找到");
     }

    }

try...catch关键字

Throwable处理异常的三个方法

  public static void main(String[] args)  {
        try {
            test("c:\\a.txt111");
        } catch (FileNotFoundException e) {
            System.out.println(e.getMessage());
            System.out.println(e.toString());
            e.printStackTrace();
        }
    }
    public static  void test(String filrName) throws FileNotFoundException{
     if (!filrName.equals("c:\\a.txt")){
         throw new FileNotFoundException("文件没找到");
     }

    }

![Throwable处理异常的三个方法(https://upload-images.jianshu.io/upload_images/16609281-229269a397216b69.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)

finally 代码块

  public static void main(String[] args)  {
        try {
            test("c:\\a.txt111");
        } catch (FileNotFoundException e) {
            System.out.println(e.getMessage());
            System.out.println(e.toString());
            e.printStackTrace();
        }
        finally {
            System.out.println("肯定执行");
        }
    }
    public static  void test(String filrName) throws FileNotFoundException{
     if (!filrName.equals("c:\\a.txt")){
         throw new FileNotFoundException("文件没找到");
     }

    }

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注意事项：finally里面有return语句

子父类异常

子父类异常

自定义异常

package com.mujiachao;

public class RegisterExcetion extends Exception{
    public RegisterExcetion() {
    }

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

···
public static void main(String[] args) {
test();
}
public static void test(){
String[] username={"张三","李四","王五"};
System.out.println("请输入要注册的用户名：");
Scanner scanner = new Scanner(System.in);
String next = scanner.next();
for (String s : username) {
if (s.equals(next)){
try {
throw new RegisterExcetion("用户名已存在");
} catch (RegisterExcetion registerExcetion) {
registerExcetion.printStackTrace();
return;
}
}
}
System.out.println("恭喜注册成功");
}
···

自定义异常