How can I throw a general exception in Java

Question

Consider this simple program  The program has two files  File Vehicle java class Vehicle       private int speed   0      private int maxSpeed   100       public int getSpeed                 return speed             public int getMaxSpeed                 return maxSpeed             public void speedUp int increment                if speed   increment  gt  maxSpeed                  Throw exception          else              speed    increment                       public void speedDown int decrement                if speed - decrement  lt  0                  Throw exception          else              speed -  decrement                     File HelloWorld java public class HelloWorld                    param args             public static void main String   args             Vehicle v1   new Vehicle            Vehicle v2   new Vehicle                    Do something                 Print something useful  TODO         System out println v1 getSpeed               As you can see in the first class  I have added a comment   quot    throw exception quot   where I would like to throw an exception  Do I have to define my own class for exceptions or is there some general exception class in Java I can use

User · Answer

Java has a large number of built-in exceptions for different scenarios   In this case  you should throw  an IllegalArgumentException  since the problem is that the caller passed a bad parameter

User · Answer

Well  there are lots of exceptions to throw  but here is how you throw an exception  throw new IllegalArgumentException  quot INVALID quot     Also  yes  you can create your own custom exceptions  A note about exceptions  When you throw an exception  like above  and you catch the exception  the String that you supply in the exception can be accessed throw the getMessage   method  try      methodThatThrowsException     catch IllegalArgumentException e      e getMessage

User · Answer

You can define your own exception class extending java lang Exception  that s for a checked exception - these which must be caught   or extending java lang RuntimeException - these exceptions does not have to be caught  The other solution is to review the Java API and finding an appropriate exception describing your situation  in this particular case I think that the best one would be IllegalArgumentException

User · Answer

You could create your own Exception class   public class InvalidSpeedException extends Exception      public InvalidSpeedException String message        super message            In your code   throw new InvalidSpeedException  TOO HIGH

User · Answer

It really depends on what you want to do with that exception after you catch it  If you need to differentiate your exception then you have to create your custom Exception  Otherwise you could just throw new Exception  message goes here

User · Answer

You could use IllegalArgumentException   public void speedDown int decrement        if speed - decrement  lt  0           throw new IllegalArgumentException  Final speed can not be less than zero         else          speed -  decrement

User · Answer

The simplest way to do it would be something like  throw new java lang Exception     However  the following lines would be unreachable in your code  So  we have two ways    Throw a generic exception at the bottom of the method  Throw a custom exception in case you don t want to do 1

User · Answer

It depends  You can throw a more general exception  or a more specific exception  For simpler methods  more general exceptions are enough  If the method is complex  then  throwing a more specific exception will be reliable

[java] How can I throw a general exception in Java?

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