Here's an example:

public void someMethod()
{
  try
  {
    // some code, which may throw a NullPointerException
    System.out.println("1");
    throw new NullPointerException("just testing");
    System.out.println("2");
  }
  catch (NullPointerException npe)
  {
    System.out.println("Encountered a NullPointerException: " + npe.getMessage());
  }
  System.out.println("3");
}

This code prints:

1
Encountered a NullPointerException: just testing
3

If you wouldn't catch the exception with a try-catch block, the execution would stop abruptly after printing "1".