Java中的自定义异常
您可以使用Java创建自己的异常，这些异常称为用户定义的异常或自定义异常。
要创建用户定义的异常，请扩展上述类之一。要显示消息，请重写toString()方法，或者以String格式绕过消息来调用超类参数化的构造函数。
MyException(String msg){
super(msg);
}
Or,
public String toString(){
return " MyException [Message of your exception]";
}然后，在需要引发此异常的其他类中，创建创建的自定义异常类的对象，然后使用throw关键字引发该异常。
MyException ex = new MyException ();
If(condition……….){
throw ex;
}自定义已检查和自定义未检查
所有异常都必须是Throwable的子级。
如果要编写由Handle或DelareRule自动执行的已检查异常，则需要扩展Exception类。
如果要编写运行时异常，则需要扩展RuntimeException类。
示例：自定义检查异常
以下Java程序演示了如何创建“自定义”检查的异常。
import java.util.Scanner;
class NotProperNameException extends Exception {
NotProperNameException(String msg){
super(msg);
}
}
public class CustomCheckedException {
private String name;
private int age;
public static boolean containsAlphabet(String name) {
for (int i = 0; i < name.length(); i++) {
char ch = name.charAt(i);
if (!(ch >= 'a' && ch <= 'z')) {
return false;
}
}
return true;
}
public CustomCheckedException(String name, int age){
if(!containsAlphabet(name)&&name!=null) {
String msg = "Improper name (Should contain only characters between a to z (all small))";
NotProperNameException exName = new NotProperNameException(msg);
throw exName;
}
this.name = name;
this.age = age;
}
public void display(){
System.out.println("Name of the Student: "+this.name );
System.out.println("Age of the Student: "+this.age );
}
public static void main(String args[]) {
Scanner sc= new Scanner(System.in);
System.out.println("Enter the name of the person: ");
String name = sc.next();
System.out.println("Enter the age of the person: ");
int age = sc.nextInt();
CustomCheckedException obj = new CustomCheckedException(name, age);
obj.display();
}
}编译时异常
在编译时，以上程序生成以下异常。
CustomCheckedException.java:24: error: unreported exception NotProperNameException; must be caught or declared to be thrown throw exName; ^ 1 error
示例：自定义未经检查的异常
如果仅将自定义异常继承的类更改为RuntimeException，它将在运行时引发
class NotProperNameException extends RuntimeException {
NotProperNameException(String msg){
super(msg);
}
}如果您通过使用上面的代码替换NotProperNameException类并运行它来运行先前的程序，它将生成以下运行时异常。
运行时异常
Enter the name of the person: Krishna1234 Enter the age of the person: 20 Exception in thread "main" july_set3.NotProperNameException: Improper name (Should contain only characters between a to z (all small)) at july_set3.CustomCheckedException.<init>(CustomCheckedException.java:25) at july_set3.CustomCheckedException.main(CustomCheckedException.java:41)