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POWhat parts of the JLS justify being able to throw checked exceptions as if they were unchecked?
 

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  1. POWhat parts of the JLS justify being able to throw checked exceptions as if they were unchecked?
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    <p>I have <a href="http://java.dzone.com/articles/throw-checked-exceptions">recently discovered and blogged about the fact</a> that it is possible to sneak a checked exception through the javac compiler and throw it where it mustn't be thrown. This compiles and runs in Java 6 and 7, throwing a <code>SQLException</code> without <code>throws</code> or <code>catch</code> clause:</p> <pre><code>public class Test { // No throws clause here public static void main(String[] args) { doThrow(new SQLException()); } static void doThrow(Exception e) { Test.&lt;RuntimeException&gt; doThrow0(e); } static &lt;E extends Exception&gt; void doThrow0(Exception e) throws E { throw (E) e; } } </code></pre> <p>The generated bytecode indicates that the JVM doesn't really care about checked / unchecked exceptions:</p> <pre><code>// Method descriptor #22 (Ljava/lang/Exception;)V // Stack: 1, Locals: 1 static void doThrow(java.lang.Exception e); 0 aload_0 [e] 1 invokestatic Test.doThrow0(java.lang.Exception) : void [25] 4 return Line numbers: [pc: 0, line: 11] [pc: 4, line: 12] Local variable table: [pc: 0, pc: 5] local: e index: 0 type: java.lang.Exception // Method descriptor #22 (Ljava/lang/Exception;)V // Signature: &lt;E:Ljava/lang/Exception;&gt;(Ljava/lang/Exception;)V^TE; // Stack: 1, Locals: 1 static void doThrow0(java.lang.Exception e) throws java.lang.Exception; 0 aload_0 [e] 1 athrow Line numbers: [pc: 0, line: 16] Local variable table: [pc: 0, pc: 2] local: e index: 0 type: java.lang.Exception </code></pre> <p>The JVM accepting this is one thing. But I have some doubts whether <em>Java-the-language</em> should. Which parts of the JLS justify this behaviour? Is it a bug? Or a well-hidden "feature" of the Java language?</p> <p>My feelings are:</p> <ul> <li><code>doThrow0()</code>'s <code>&lt;E&gt;</code> is bound to <code>RuntimeException</code> in <code>doThrow()</code>. Hence, no <code>throws</code> clause along the lines of <a href="http://docs.oracle.com/javase/specs/jls/se7/html/jls-11.html#jls-11.2">JLS §11.2</a> is needed in <code>doThrow()</code>.</li> <li><code>RuntimeException</code> is assignment-compatible with <code>Exception</code>, hence no cast (which would result in a <code>ClassCastException</code>) is generated by the compiler.</li> </ul>
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    1. USLukas Eder
    1. USLukas Eder
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      1. POWhat parts of the JLS justify being able to throw checked exceptions as if they were unchecked?
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      1. USdcernahoschi
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    1. COBecause `RuntimeException` extends Exception this is possible. But it is allowed.
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      1. POWhat parts of the JLS justify being able to throw checked exceptions as if they were unchecked?
      1. USAmit Deshpande
    2. COThe JVM couldn't care less, that is for sure. It's only a compile-time validation. I like this, maybe I can adapt it to finally be able to avoid all those idiotic try-catch e-throw new RuntimeException(e)!
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      1. POWhat parts of the JLS justify being able to throw checked exceptions as if they were unchecked?
      1. USMarko Topolnik
    3. CODude, this is a nice way to get both reputations on SO _and_ click-through on your blog ;)
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      1. USSaintali
 

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