Saturday, 28 July 2012

About Using System.Exit() in Try Catch Finally Java Statements

This post is an attempt at summarizing issues around using the Java system.exit() statements inside try {...} catch (...) {...} finally {...} statements.

We will use the following piece of code:
public class TryCatchFinallySystemExit {

  public static void main(String[] args) {

    System.setSecurityManager(new SecurityManager() {

      @Override
      public void checkPermission(Permission perm) { }

      @Override
      public void checkExit(int status) {
        // throw new SecurityException();
      }

    });

    System.out.println("Before Check");
    check();
    System.out.println("After Check");

  }

  public static void check() {

    try {

      System.out.println("Before System.exit(-1)");
      System.exit(-1);
      System.out.println("After System.exit(-1)");

    } catch(Throwable t) {

      System.out.println("Before System.exit(-2)");
      System.exit(-2);
      System.out.println("After System.exit(-2)");

    } finally {

      System.out.println("Before System.exit(-3)");
      System.exit(-3);
      System.out.println("After System.exit(-3)");

    }

    System.out.println("After try statement");

  }

}

The main method implements a SecurityManager, then calls the check() method. If we run this application as is, the output is the following:

Before Check
Before System.exit(-1)

We can conclude that:
  • System.exit(-1) is the last statement excuted.
  • Catch and Finally statements are not called.
  • The check() method does not return.

If we uncomment the throw new SecurityException(); and execute the application again, we get:

Before Check
Before System.exit(-1)
Before System.exit(-2)
Before System.exit(-3)

We can conclude that:
  • The SecurityException get the catch and finally statements to be executed.
  • Statements after System.exit() statements are not executed.
  • The check() method does not return.

For return, continue and break statements in try statements, see this post.

Disclaimer: this post contains information from personal notes and information available on StackOverflow.com.