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copied!<p>Here is a simple example of how to use the exception:</p> <pre><code>class IntegerExceptionTest { public static void main(String[] args) { try { throw new IntegerException(42); } catch (IntegerException e) { assert e.getValue() == 42; } } } </code></pre> <p>The body of the TRy statement throws the exception with a given value, which is caught by the catch clause.</p> <p>In contrast, the following definition of a new exception is prohibited, because it creates a parameterized type:</p> <pre><code>class ParametricException<T> extends Exception { // compile-time error private final T value; public ParametricException(T value) { this.value = value; } public T getValue() { return value; } } </code></pre> <p>An attempt to compile the above reports an error:</p> <pre><code>% javac ParametricException.java ParametricException.java:1: a generic class may not extend java.lang.Throwable class ParametricException<T> extends Exception { // compile-time error ^ 1 error </code></pre> <p>This restriction is sensible because almost any attempt to catch such an exception must fail, because the type is not reifiable. One might expect a typical use of the exception to be something like the following:</p> <pre><code>class ParametricExceptionTest { public static void main(String[] args) { try { throw new ParametricException<Integer>(42); } catch (ParametricException<Integer> e) { // compile-time error assert e.getValue()==42; } } } </code></pre> <p>This is not permitted, because the type in the catch clause is not reifiable. At the time of this writing, the Sun compiler reports a cascade of syntax errors in such a case:</p> <pre><code>% javac ParametricExceptionTest.java ParametricExceptionTest.java:5: <identifier> expected } catch (ParametricException<Integer> e) { ^ ParametricExceptionTest.java:8: ')' expected } ^ ParametricExceptionTest.java:9: '}' expected } ^ 3 errors </code></pre> <p>Because exceptions cannot be parametric, the syntax is restricted so that the type must be written as an identifier, with no following parameter.</p>

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