目录

自定义异常

1. 为什么要使用自定义异常

自定义运行时异常语法

自定义检查异常语法

示例

2. 异常使用注意事项

Java SE文章参考:Java SE入门及基础知识合集-CSDN博客

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自定义异常

1. 为什么要使用自定义异常

自定义运行时异常语法

public class 类名 extends RuntimeException {}

自定义检查异常语法

public class 类名 extends Exception {}

示例

package com . we . exception ;

/**

* 用户名不存在异常

*

* 异常命名规范：场景描述 +Exception

*/

public class UsernameNotFoundException extends Exception {

        public UsernameNotFoundException (){}

        public UsernameNotFoundException ( String msg ){

                super ( msg );

        }

}

package com . we . exception ;

/**

* 账号或密码错误异常

*/

public class BadCredentialsException extends Exception {

        public BadCredentialsException (){

        }

        public BadCredentialsException ( String msg ){

                super ( msg );

        }

}

package com . we . exception ;

import java . util . Scanner ;

public class Login {

        private static Scanner sc = new Scanner ( System . in );

        public static void main ( String [] args ) {

                System . out . println ( " 请输入账号： " );

                String username = sc . next ();

                System . out . println ( " 请输入密码： " );

                String password = sc . next ();

                try {

                        login ( username , password );

                } catch ( UsernameNotFoundException e ) {

                        e . printStackTrace ();

                } catch ( BadCredentialsException e ) {

                        e . printStackTrace ();

        }

}

        public static void login ( String username , String password ) throws UsernameNotFoundException , BadCredentialsException {

                if ( "admin" . equals ( username )){

                        if ( "123456" . equals ( password )){

                                System . out . println ( " 登录成功 " );

                        } else {

                                throw new BadCredentialsException ( " 账号或密码错误 " );

                        }

                } else {

                        throw new UsernameNotFoundException ( " 账号不存在 " );

                }

        }

}

2. 异常使用注意事项

1. 运行时异常可以不处理。
2. 如果父类抛出了多个异常,子类覆盖父类方法时,只能抛出相同的异常或者是该异常的子集。(与协变返回类型原理一致)
3. 父类方法没有抛出异常，子类覆盖父类该方法时也不可抛出检查异常。此时子类产生该异常，只能捕获处理，不能声明抛出

package com . we . exception ;

public class Father {

        public void eat () throws Exception {

        }

        public void sleep (){

        }

        public void login (){

        }

}

package com . we . exception ;

public class Child extends Father {

        private String username ;

        private String password ;

        public Child ( String username , String password ) {

                this . username = username ;

                this . password = password ;

        }

        @Override

        public void eat () throws UsernameNotFoundException {

        }

        //父类中的方法没有声明抛出异常，子类中方法可以声明抛出运行时异常

        @Override

        public void sleep () throws RuntimeException {

        }

        //父类中的方法没有声明抛出异常，子类中方法不能声明抛出检查异常

        @Override

        public void login () {

                try {

                        Login . login ( username , password );

                } catch ( UsernameNotFoundException e ) {

                        e . printStackTrace ();

                } catch ( BadCredentialsException e ) {

                        e . printStackTrace ();

                }

        }

}

Java SE文章参考:Java SE入门及基础知识合集-CSDN博客