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基本原则

自定义异常类通常需要编写几个重载的构造器。

自定义的异常通过

throw

抛出。

自定义异常最重要的是异常类的名字，当异常出现时，可以根据名字判断异常类型。

简单的代码案例

继承了Exception的自定义异常处理类MyException

class MyException extends Exception {
     //异常信息
    private String message;
    public MyException(String message) {
        super(message);
        this.message = message;
    }
}

调用自定义的异常处理类

public class UseMyException{
    public void regist(int num) throws MyException {
        if (num < 0)
            throw new MyException("输入参数有误，不能为负值");
        else
            System.out.println(num);
	}
}

try-catch自定义的异常处理类

public class UseMyExceptionTest {
    @Test
    public void test(){
        try{
            UseMyException useMyException=new UseMyException();
            useMyException.regist(-1);
        }catch (MyException me){
            System.out.println("MyException:"+me.getMessage());
        }
    }
}

测试结果

包含更多现场信息的异常类定义

class UseMyException{
    public void regist(int num) throws MyException {
        if (num < 0)
            throw new MyException("输入参数有误，不能为负值",1);
        else
            System.out.println(num);
    }
    public void regist2(int id) throws AdditionalInformationException {
        if (id < 0)
            throw new AdditionalInformationException("输入参数有误，不能为负值",id);
        else
            System.out.println(id);
    }
}
class AdditionalInformationException extends Exception {
    private int amount;
    public AdditionalInformationException(String message,int amount) {
        super(message);
        this.amount = amount;
    }
    public double getAmount(){
        return amount;
    }
}
class AdditionalInformationExceptionTest {
    public static void main(String[] args) {
        try{
            UseMyException useMyException=new UseMyException();
            useMyException.regist2(-1);
        }catch (AdditionalInformationException me){
            System.out.println("AdditionalInformationException:"
                                +me.getMessage()+" 错误的参数值为："
                                +me.getAmount());
        }
    }
}

测试结果