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    <p>It tells the clients of your class that the DoBlah method can throw a BlahException or <em>any other exception that extends it</em>. </p> <p>If it's a checked exception, the compiler will require that they wrap calls to this method in a try/catch block. If it's unchecked, they can choose to not catch the exception, but they have to be aware that if they don't it'll be bubbled further up the call stack.</p> <p>It doesn't say anything about unchecked exceptions like NullPointException or errors. Those can always be thrown as well. They aren't required in the throws clause.</p> <p>This code shows how it works: </p> <p>ExceptionDemo.java:</p> <pre><code>package exceptions; public class ExceptionDemo { public static void main(String[] args) { ExceptionDemo demo = new ExceptionDemo(); try { // Removing the try/catch will result in a compilation error demo.doChecked(); } catch (CheckedException e) { e.printStackTrace(); } // Note: Not inside a try/catch, in spite of the throws clause demo.doUnchecked(); } public void doChecked() throws CheckedException { System.out.println("doing something that may throw a checked exception"); } // Note: "throws" clause is unnecessary for an unchecked exception public void doUnchecked() throws UncheckedException { System.out.println("doing something that may throw an unchecked exception"); } } </code></pre> <p>CheckedException.java: </p> <pre><code>package exceptions; public class CheckedException extends Exception { public CheckedException() { super(); } public CheckedException(String message) { super(message); } public CheckedException(String message, Throwable cause) { super(message, cause); } public CheckedException(Throwable cause) { super(cause); } } </code></pre> <p>UncheckedException.java: </p> <pre><code>package exceptions; public class UncheckedException extends RuntimeException { public UncheckedException() { super(); } public UncheckedException(String message) { super(message); } public UncheckedException(String message, Throwable cause) { super(message, cause); } public UncheckedException(Throwable cause) { super(cause); } } </code></pre>
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    1. POThe throws keyword for exceptions in Java
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    1. COBizarrely, there's no mention at all that I can find of Exceptions in the Java Tutorial (http://java.sun.com/docs/books/tutorial/java/TOC.html). What a peculiar omission.
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    2. COJust for my curiosity, how exactly do you specify whether a (user-defined) exception is supposed to be checked or unchecked? Is it as simple as having it appear in that "throws" section, or is there something you have to do in the exception class itself?
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    3. CO@skaffman Exceptions are covered in Essential Java Classes (http://java.sun.com/docs/books/tutorial/essential/index.html) rather than Learning the Java Language.
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