Java: custom-exception-error
-
26-09-2019 - |
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() );
}
}
}
Solution
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 ofException
- 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.
OTHER TIPS
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
.)
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