Checked Exceptions

Please keep in mind that it is Java bytecode that executes, not the Java source code. However the bytecode file contains information about how lines of source code and bytecodes correspond. The other line numbers are not very useful for us because they refer to the source code for the parseInt() method (written at Sun Microsystems) that is not part of our file.

Some exception types are checked exceptions, which means that a method must do something about them. The compiler checks each method to be sure that it does. There are two things a method can do with a checked exception:

1. Handle the exception in a catch{} block, or
2. throw the exception to the caller of the method.

For example, an IOException is a checked exception. In the past your programs have done something like this:

public class DoesIO
{
  public static void main ( String[] a ) throws IOException
  {
    BufferedReader stdin = 
        new BufferedReader ( new InputStreamReader( System.in ) );

    // More Java statements ...
  }
}

The reserved word throws says that this method does not catch the IOException, and that if one occurs in this method it will be thrown to the method that called this one. (In this example, it will be thrown back to the Java runtime system.)