How to create a custom exception type in Java

Question

I would like to create a custom exception in Java  how do I do it        try        String word reader readLine     if word contains           create custom exception      catch      When I create my custom exception with throw new     I obtain the error unreported exception   must be caught or declared to be thrown

User · Answer

Great answers about creating custom exception classes  If you intend to reuse the exception in question then I would follow their answers advice  However  If you only need a quick exception thrown with a message then you can use the base exception class on the spot  String word reader readLine     if word contains           create custom exeception     throw new Exception  My one time exception with some message

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You have to define your exception elsewhere as a new class  public class YourCustomException extends Exception     Required inherited methods here     Then you can throw and catch YourCustomException as much as you d like

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You need to create a class that extends from Exception  It should look like this   public class MyOwnException extends Exception       public MyOwnException                  public MyOwnException  String message            super  message              public MyOwnException  Throwable cause            super  cause              public MyOwnException  String message  Throwable cause            super  message  cause             Your question does not specify if this new exception should be checked or unchecked   As you can see here  the two types are different    Checked exceptions are meant to flag a problematic situation that should be handled by the developer who calls your method  It should be possible to recover from such an exception  A good example of this is a FileNotFoundException  Those exceptions are subclasses of Exception  Unchecked exceptions are meant to represent a bug in your code  an unexpected situation that you might not be able to recover from  A NullPointerException is a classical example  Those exceptions are subclasses of RuntimeException   Checked exception must be handled by the calling method  either by catching it and acting accordingly  or by throwing it to the calling method  Unchecked exceptions are not meant to be caught  even though it is possible to do so

User · Answer

An exception is a class like any other class  except that it extends from Exception  So if you create your own class  public class MyCustomException extends Exception   you can throw such an instance with     throw new MyCustomException              using whatever constructor params you decide to use   And this might be an interesting read

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You can create you own exception by inheriting from java lang Exception  Here is an example that can help you do that

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As a careful programmer will often throw an exception for a special occurrence  it worth mentioning some general purpose exceptions like IllegalArgumentException and IllegalStateException and UnsupportedOperationException  IllegalArgumentException is my favorite   throw new IllegalArgumentException  Word contains blank      word

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You should be able to create a custom exception class that extends the Exception class  for example   class WordContainsException extends Exception            Parameterless Constructor       public WordContainsException                Constructor that accepts a message       public WordContainsException String message                   super message                Usage   try        if word contains                        throw new WordContainsException             catch WordContainsException ex             Process message however you would like

User · Answer

You just need to create a class which extends Exception  for a checked exception  or any subclass of Exception  or RuntimeException  for a runtime exception  or any subclass of RuntimeException   Then  in your code  just use   if  word contains           throw new MyException  some message        Read the Java tutorial  This is basic stuff that every Java developer should know  http   docs oracle com javase tutorial essential exceptions

User · Answer

Since you can just create and throw exceptions it could be as easy as  if   word contains               throw new RuntimeException    Word contains one or more spaces          If you would like to be more formal  you can create an Exception class  class SpaceyWordException extends RuntimeException        Either way  if you use RuntimeException  your new Exception will be unchecked

[java] How to create a custom exception type in Java?

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