Lab: XMLTree Methods

Objectives

The objective of this lab is to familiarize yourself with the XMLTree methods and how they can be used to extract information from an XMLTree object.

The Problem

For this lab, you will load an XMLTree object from an XML URL; then, from this object, you will extract various pieces of information using the XMLTree methods and you will output that information to the console. Make sure you successfully and correctly complete each task before moving on to the next.

Setup

Follow these steps to set up a project for this lab.

1. Create a new Eclipse project by copying ProjectTemplate. Name the new project XMLTreeExploration.
2. Open the src folder of this project and then open (default package). As a starting point you should use ProgramWithIO.java. Rename it XMLTreeExploration and delete the other files from the project.
3. In a browser window open the documentation for the XMLTree component . You will need to refer to it throughout the lab.

Method

Edit XMLTreeExploration.java to perform the following tasks. Note that at the beginning you will hard code specific method calls to solve specific tasks that rely on the input being the specific input you are manipulating.

Getting Started: Constructing and Displaying an XMLTree

1. Declare an XMLTree variable, name it xml, and initialize it with an object of XMLTree1 type constructed from the URL https://cse22x1.engineering.osu.edu/2221/web-sw1/extras/instructions/xmltree-model/columbus-weather.xml:

   XMLTree xml =
   new XMLTree1("https://cse22x1.engineering.osu.edu/2221/web-sw1/"
       + "extras/instructions/xmltree-model/columbus-weather.xml");
   

2. Two instance methods in the XMLTree component are particularly useful when trying to visualize the value of an XMLTree object: toString which produces a textual representation of the XMLTree and can be used to output it to an output stream (e.g., a SimpleWriter) and display which opens a new window and displays the XMLTree in a way similar to the XMLTree Viewer application you used in the last lab. See the documentation for the complete description of these methods.

3. Modify your program so that it outputs the XMLTree xml to the console using the open output stream and it also displays the XMLTree in a new window.

4. Run your current program and compare the textual XML output with the tree representation in the displayed window. Once you have verified that the two views essentially provide the same information, you can comment out the statement that produces the textual output to the console (you won't need it for the rest of the lab).

The Root

1. A node in an XMLTree has a label which can be either a tag or text. Two XMLTree instance methods are useful in determining the nature of a node: isTag which tells us whether the root node of the XMLTree is a tag or not (i.e., text) and label which returns the label (tag or text) of the root node of the XMLTree.
2. Modify your program so that, using these methods, it outputs whether the root of the XMLTree xml is a tag or text and the label of the root of the XMLTree xml.
3. Verify that the output matches your expectations by checking the root node in the XMLTree display.

The Children

1. Every tag node (a node whose label is a tag) in an XMLTree can have 0 or more children, i.e., subtrees that are also XMLTrees. Two XMLTree instance methods are used to access the children of the root: numberOfChildren returns the number of children of the root node of the XMLTree and child returns a child of the root node of the XMLTree given the index (starting at 0) of the child among all the children.
2. Modify the program as follows:
   1. Declare a new XMLTree variable, name it results, and initialize it to the results child of the root node of the XMLTree xml (should be the first child, but you need to verify that in the displayed tree).
   2. Declare a new XMLTree variable, name it channel, and initialize it to the channel child of the XMLTree results (should be the first child, but you need to verify that in the displayed tree).
   3. Output the number of children of the root of the XMLTree channel.
   4. Then declare another XMLTree variable, name it title, and initialize it to the title child of the root node of the channel XMLTree (it should be the second child, but you need to verify that in the displayed tree).
   5. Declare a fourth XMLTree variable, name it titleText, and initialize it to the text child of the root node of the title XMLTree.
   6. Finally, output the label of the titleText XMLTree.
3. Now for a little challenge: can you achieve the same result of the previous step with a single statement directly from XMLTree xml? In other words, output the same string of characters with just one statement involving variable xml. (Note: this is not necessarily good programming practice, but it is worth knowing that you can do it.) Add the new statement; do not delete or comment out those you entered earlier. (If you are not sure how to do this, see Slide #50 in XMLTree Methods.)

The Attributes

1. Every tag node (a node whose label is a tag) in an XMLTree can have 0 or more attributes, where each attribute has a name and a value. Two XMLTree instance methods are used to access individual attributes of the root: hasAttribute which, given a String argument, returns whether the root node of the XMLTree has an attribute with that name and attributeValue which, given a String argument, returns the value of the given attribute of the root node of the XMLTree.
2. Modify the program as follows:
   1. Declare a new XMLTree variable, name it astronomy, and initialize it to the yweather:astronomy child of the root node of the channel XMLTree.
   2. Using the hasAttribute method, output whether the root of the astronomy XMLTree has an attribute named "sunset" and whether it has an attribute named "midday".
   3. Output the values of attributes sunrise and sunset of the root of the astronomy XMLTree.

One More Challenge

1. Implement the following static method that extracts the middle child of the given XMLTree and outputs to the given output stream

   1. the middle child's label,
   2. whether the middle child's label is a tag or text, and
   3. if the middle child's label is a tag, its number of children

   Use the numberOfChildren method to determine the index of the middle child.

   /**
    * Output information about the middle child of the given {@code XMLTree}.
    *
    * @param xt
    *            the {@code XMLTree} whose middle child is to be printed
    * @param out
    *            the output stream
    * @updates out.content
    * @requires
    * [the label of the root of xt is a tag]  and
    * [xt has at least one child]  and  out.is_open
    * @ensures
    * out.content = #out.content * [the label of the middle child
    *   of xt, whether the root of the middle child is a tag or text,
    *   and if it is a tag, the number of children of the middle child]
    */
   private static void printMiddleNode(XMLTree xt, SimpleWriter out) {...}
   

2. Modify the main program to output information about the middle child of the channel XMLTree by calling the printMiddleNode static method.

3. Verify in the displayed tree that the output is correct.

Additional Activities

One Last Challenge

1. Implement the following static method that outputs all the attributes (names and values) of the root of a given XMLTree. For this task, you will need to use the last instance method provided by the XMLTree component, namely, attributeNames. (If you are not sure how to do this, see Slides #52-60 in XMLTree Methods.)

   /**
    * Output all attributes names and values for the root of the given
    * {@code XMLTree}.
    *
    * @param xt
    *            the {@code XMLTree} whose root's attributes are to be printed
    * @param out
    *            the output stream
    * @updates out.content
    * @requires [the label of the root of xt is a tag] and out.is_open
    * @ensures
    * out.content =
    *   #out.content * [the name and value of each attribute of the root of xt]
    */
   private static void printRootAttributes(XMLTree xt, SimpleWriter out) {...}
   

2. Modify the main program to output information about the forecast for February 2, 2017 as follows:

   1. Declare a new XMLTree variable, name it item, and initialize it to the item child of the root node of the channel XMLTree.
   2. Declare another XMLTree variable, name it forecast, and initialize it to the yweather:forecast child of the root node of the item XMLTree with the weather forecast for February 2, 2017.
   3. Call the printRootAttributes static method to output the attributes of the root node of the forecast XMLTree.

3. Verify in the displayed tree that the output is correct.