Finally

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layout: default title: finally

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A try/catch block optionally can be followed by a finally block.

• The finally block executes whether or not an exception occurs.

try {
  mayCrash();
  System.out.println("No exception.");
}
catch (FileNotFoundException e) {
  System.out.println("Exception occurred.");
  }
finally {
  System.out.println("mayCrash() was called.");
}

The finally block always executes, unless the JVM itself exits in the try or a catch.

try {
  mayCrash();
  System.out.println("No exception, returning.");
  return; // Return from method....
}
catch (FileNotFoundException e) {
  System.out.println("Exception occurred, returning.");
  return; // Return from method....
}
finally {
  // ... but execute the finally block on the way out.
  System.out.println("finally block: mayCrash() was called.");
}

Exception occurred, returning.
finally block: mayCrash() was called.

A finally block comes after all catch blocks.

try {
  mayCrash();
}
finally {
  System.out.println("Hello from finally!");
}
catch (Exception e) {  // WILL NOT COMPILE: Syntax error.
  e.printStackTrace();
}

• A try can be followed by finally, with no catch blocks.

try {
  System.out.println("Trying to print, then returning.");
  return;
}
finally {
  System.out.println("Hello from finally!");
}

Trying to print, then returning.
Hello from finally!

Drill

Exceptions/com.example.exceptions.drills.FinallyDrill * Run FinallyDrill and examine the stack trace. Does main finish executing? * In runMethod add a finally block that uses System.err to print a message. Run FinallyDrill again. Does the new message print? Does main finish executing? * In launch, surround the call to runMethod with a try/catch. (Tip: in Eclipse, highlight the method call line, right-click, and choose Surround With and Try/catch block). In the catch block, use System.err to print a message, followed by return. Run and examine the results. * Add a finally to the try/catch in launch, which uses System.err to print a message, followed by return. Does the message print? Does main complete? * In the catch block in launch, change the return to System.exit(1). What happens when you run it?

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