public class StringTest
{
    public static void main( String[] args )
    {
        String s = "moose";

        // The next line doesn't compile, because [] notation doesn't work with String.
        // s[0] = 'g';

        // This also fails to compile, because String objects are unmodifiable
        // after they're initialized (and thus String has no setCharAt method).
        // s.setCharAt( 0, 'g' );


        StringBuffer sb = new StringBuffer( "moose" );

        // But StringBuffer gives you the ability to modify your string after initialization.
        sb.setCharAt( 0, 'g' );
        System.out.println( sb );
    }
}