An exception in a ``++throws++`` declaration in Java is superfluous if it is:

* listed multiple times
* a subclass of another listed exception
* completely unnecessary because the declared exception type cannot actually be thrown


== Noncompliant Code Example

----
void foo() throws MyException, MyException {}  // Noncompliant; should be listed once
void bar() throws Throwable, Exception {}  // Noncompliant; Exception is a subclass of Throwable
----


== Compliant Solution

----
void foo() throws MyException {}
void bar() throws Throwable {}
----


== Exceptions

The rule will not raise any issue for exceptions that cannot be thrown from the method body:

* in overriding and implementation methods
* in interface ``++default++`` methods
* in non-private methods that only ``++throw++``, have empty bodies, or a single return statement.
* in overridable methods (non-final, or not member of a final class, non-static, non-private), if the exception is documented with a proper JavaDoc

Also, the rule won't raise issues on ``++RuntimeException++``, or one of its descendants, because explicating runtime exceptions which could be thrown can ultimately help the method's users, and can even be considered as good practice.

----
class A extends B {
  @Override
  void doSomething() throws IOException {
    compute(a);
  }

  public void foo() throws IOException {}

  public void qix() throws MyRuntimeException {}

  protected void bar() throws IOException {
    throw new UnsupportedOperationException("This method should be implemented in subclasses");
  }

  Object foobar(String s) throws IOException {
    return null;
  }

  /**
   * @throws IOException Overriding classes may throw this exception if they print values into a file
   */
  protected void print() throws IOException { // no issue, method is overridable and the exception has proper javadoc
    System.out.println("foo");
  }
}
----


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== Comments And Links
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