exceptions - What's finally for

The finally clause is necessary to clean up something other than memory. Examples include an open file or network connection, something you’ve drawn on the screen, or even a switch in the outside world: 

// exceptions/Switch.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.

public class Switch {
  private boolean state = false;

  public boolean read() {
    return state;
  }

  public void on() {
    state = true;
    System.out.println(this);
  }

  public void off() {
    state = false;
    System.out.println(this);
  }

  @Override
  public String toString() {
    return state ? "on" : "off";
  }
}

// exceptions/OnOffException1.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
public class OnOffException1 extends Exception {}

 

// exceptions/OnOffException2.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
public class OnOffException2 extends Exception {}

// exceptions/OnOffSwitch.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Why use finally?

public class OnOffSwitch {
  private static Switch sw = new Switch();

  public static void f() throws OnOffException1, OnOffException2 {}

  public static void main(String[] args) {
    try {
      sw.on();
      // Code that can throw exceptions...
      f();
      sw.off();
    } catch (OnOffException1 e) {
      System.out.println("OnOffException1"); // does not output
      sw.off();
    } catch (OnOffException2 e) {
      System.out.println("OnOffException2"); // does not output
      sw.off();
    }
  }
}
/* Output:
on
off
*/

// exceptions/WithFinally.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Finally Guarantees cleanup

public class WithFinally {
  static Switch sw = new Switch();

  public static void main(String[] args) {
    try {
      sw.on();
      // Code that can throw exceptions...
      OnOffSwitch.f();
    } catch (OnOffException1 e) {
      System.out.println("OnOffException1"); // does not output
    } catch (OnOffException2 e) {
      System.out.println("OnOffException2"); // does not output
    } finally {
      sw.off();
    }
  }
}
/* Output:
on
off
*/

references:

1. On Java 8 - Bruce Eckel

2. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/exceptions/Switch.java

3. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/exceptions/OnOffException1.java

4. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/exceptions/OnOffException2.java

5. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/exceptions/OnOffSwitch.java

7. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/exceptions/WithFinally.java