How to define custom exception class in Java the easiest way

Question

I m trying to define my own exception class the easiest way  and this is what I m getting   public class MyException extends Exception     public class Foo     public bar   throws MyException       throw new MyException  try again please            This is what Java compiler says   cannot find symbol  constructor MyException java lang String    I had a feeling that this constructor has to be inherited from java lang Exception  isn t it

User · Answer

A typical custom exception I d define is something like this   public class CustomException extends Exception        public CustomException String message            super message              public CustomException String message  Throwable throwable            super message  throwable              I even create a template using Eclipse so I don t have to write all the stuff over and over again

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If you use the new class dialog in Eclipse you can just set the Superclass field to java lang Exception and check  Constructors from superclass  and it will generate the following   package com example exception   public class MyException extends Exception        public MyException                TODO Auto-generated constructor stub            public MyException String message            super message              TODO Auto-generated constructor stub            public MyException Throwable cause            super cause              TODO Auto-generated constructor stub            public MyException String message  Throwable cause            super message  cause              TODO Auto-generated constructor stub            In response to the question below about not calling super   in the defualt constructor  Oracle has this to say      Note  If a constructor does not explicitly invoke a superclass constructor  the Java compiler automatically inserts a call to the no-argument constructor of the superclass

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Exception class has two constructors    public Exception   -- This constructs an Exception without any additional information Nature of the exception is typically inferred from the class name  public Exception String s  -- Constructs an exception with specified error message A detail message is a String that describes the error condition for this particular exception

User · Answer

No  you don t  inherit  non-default constructors  you need to define the one taking a String in your class  Typically you use super message  in your constructor to invoke your parent constructor  For example  like this   public class MyException extends Exception       public MyException String message            super message

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If you inherit from Exception  you have to provide a constructor that takes a String as a parameter  it will contain the error message

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package customExceptions   public class MyException extends Exception       public MyException String exc                super exc             public String getMessage                 return super getMessage                import customExceptions MyException   public class UseCustomException        MyException newExc new MyException  This is a custom exception         public UseCustomException   throws MyException               System out println  Hello Back Again with custom exception            throw newExc                public static void main String args                  try                       UseCustomException use new UseCustomException                      catch MyException myEx                        System out println  This is my custom exception     myEx getMessage

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and don t forget the easiest way to throw an exception  you don t need to create a class   if  rgb  gt  MAX  throw new RuntimeException  max color exceeded

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Reason for this is explained in the Inheritance article of the Java Platform which says        A subclass inherits all the members  fields  methods  and nested   classes  from its superclass  Constructors are not members  so they   are not inherited by subclasses  but the constructor of the superclass   can be invoked from the subclass

[java] How to define custom exception class in Java, the easiest way?

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