Variants

Figure 522. Just finally, no catch

Scanner scanner = null;
try {
  scanner = new Scanner(System.in);
   ... // Something may fail
} finally {
  if (null != scanner) {
    scanner.close(); // Clean up, save resources!
  }
}

Figure 523. try-with-resources (Java™ 7)

try (final Scanner❶  scanner❷ = new Scanner(System.in)) {
   ... // Something may fail
}❸ // implicitly calling scanner.close()

❶	Class must implement interface `AutoCloseable`.
❷	Variable `scanner`'s scope limited to block.
❸	`close()` method will be called automatically before leaving block scope.

Figure 524. Scanner implementing AutoCloseable

public class Scanner
  implements AutoCloseable ❶, ... {

  ...

  public void close() {...} ❷

}

Interface AutoCloseable {
  public void close(); // Signature, no
                       // implementation
}

❶	Promise to implement all methods being declared in `AutoCloseable`.
❷	Actually implementing a `close()` method.

Figure 525. No close() method in e.g. class String

try (final String s = new String()) { // Error: Required type: AutoCloseable; Provided: String
   ...
}

Prev	Up	Next
Exceptions and Junit	Home	Class `java.lang.Exception`

Error Handling

Variants