Java: custom-exception-error

Question

$ javac TestExceptions.java 
TestExceptions.java:11: cannot find symbol
symbol  : class test
location: class TestExceptions
            throw new TestExceptions.test("If you see me, exceptions work!");
                                    ^
1 error

Code

import java.util.*;
import java.io.*;

public class TestExceptions {
    static void test(String message) throws java.lang.Error{
        System.out.println(message);
    }   

    public static void main(String[] args){
        try {
             // Why does it not access TestExceptions.test-method in the class?
            throw new TestExceptions.test("If you see me, exceptions work!");
        }catch(java.lang.Error a){
            System.out.println("Working Status: " + a.getMessage() );
        }
    }
}

Community · Accepted Answer · 2016-08-11 16:41:11Z

6

TestExceptions.test returns type void, so you cannot throw it. For this to work, it needs to return an object of a type that extends Throwable.

One example might be:

   static Exception test(String message) {
        return new Exception(message);
    }

However, this isn't very clean. A better pattern would be to define a TestException class that extends Exception or RuntimeException or Throwable, and then just throw that.

class TestException extends Exception {
   public TestException(String message) {
     super(message);
   }
}

// somewhere else
public static void main(String[] args) throws TestException{
    try {
        throw new TestException("If you see me, exceptions work!");
    }catch(Exception a){
        System.out.println("Working Status: " + a.getMessage() );
    }
}

(Also note that all classes in package java.lang can be referenced by their class name rather than their fully-qualified name. That is, you don't need to write java.lang.)

edited Aug 11, 2016 at 16:41

CommunityBot

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answered Apr 13, 2010 at 16:37

danben

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1 Comment

danben Over a year ago

That's because String is not Throwable. See the second sentence of my answer.

Community · Accepted Answer · 2016-08-11 15:42:20Z

3

Working Code

Try this:

public class TestExceptions extends Exception {
    public TestExceptions( String s ) {
      super(s);
    }

    public static void main(String[] args) throws TestExceptions{
        try {
            throw new TestExceptions("If you see me, exceptions work!");
        }
        catch( Exception a ) {
            System.out.println("Working Status: " + a.getMessage() );
        }
    }
}

Problems

There are a number of issues with the code you posted, including:

Catching Error instead of Exception
Using a static method to construct the exception
Not extending Exception for your exception
Not calling the superclass constructor of Exception with the message

The posted code resolves those issues and displays what you were expecting.

edited Aug 11, 2016 at 15:42

CommunityBot

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answered Apr 13, 2010 at 16:38

Dave Jarvis

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