Maps

Overview

A Map is an object that maps keys to values. A map cannot contain duplicate keys, and each key can map to at most one value. A Map in WOX is the equivalent to java.util.HashMap in Java, and System.Collections.Hashtable in C#, as can be seen in the Data types mapping section. A Map is represented in a unique way, which means that it can be de-serialized either to Java or C#.

The code for the example in this section is provided in both Java and C#.

The Course class

For this section, we will use again the Course class, which has three fields: code of type int, name of type string, and term of type int.

//Java
public class Course {
    private int code;
    private String name;
    private int term;
    //constructors and methods omitted
}

//C#
public class Course {
    private Int32 code;
    private String name;
    private Int32 term;
    //constructors and methods omitted
}

Serializing a map of Course objects to XML

We will create a map of four entries: the keys will be of type int, and the values will be of type Course objects.

//Java
HashMap map = new HashMap();
map.put(6756, new Course(6756, "XML and Related Technologies", 3));
map.put(9865, new Course(9865, "Object Oriented Programming", 2));
map.put(1134, new Course(1134, "E-Commerce Programming", 2));
map.put(4598, new Course(4598, "Enterprise Component Architecture", 3));

//C#
Hashtable map = new Hashtable();
map.Add(6756, new Course(6756, "XML and Related Technologies", 3));
map.Add(9865, new Course(9865, "Object Oriented Programming", 2));
map.Add(1134, new Course(1134, "E-Commerce Programming", 2));
map.Add(4598, new Course(4598, "Enterprise Component Architecture", 3));

We use the save method of the Easy class to serialize the map to XML, and store it to the specified file.

In Java you will require woxSerializer.jar and jdom.jar files in the classpath. In C# you will require woxSerializer.dll.

//Java
String filename = "mapCourses.xml";
Easy.save(map, filename);

//C#
String filename = "mapCourses.xml";
Easy.save(map, filename);

The XML representation of the map is shown below. Note that the order of the entries may vary between the XML representation generated by WOX in Java, and the XML representation generated by WOX in C#. This is because the hash function may not be the same in both languages. This does not affect the de-serialization process, which means you could take the XML representation of the map generated by WOX in Java and de-serialize it in C#; or viceversa.

<object type="map" id="0">
    <object type="entry">
        <object type="int" value="1134" id="1" />
        <object type="Course" id="2">
            <field name="code" type="int" value="1134" />
            <field name="name" type="string" value="E-Commerce Programming" />
            <field name="term" type="int" value="2" />
        </object>
    </object>
    <object type="entry">
        <object type="int" value="6756" id="3" />
        <object type="Course" id="4">
            <field name="code" type="int" value="6756" />
            <field name="name" type="string" value="XML and Related Technologies" />
            <field name="term" type="int" value="3" />
        </object>
    </object>
    <object type="entry">
        <object type="int" value="4598" id="5" />
        <object type="Course" id="6">
            <field name="code" type="int" value="4598" />
            <field name="name" type="string" value="Enterprise Component Architecture" />
            <field name="term" type="int" value="3" />
        </object>
    </object>
    <object type="entry">
        <object type="int" value="9865" id="7" />
        <object type="Course" id="8">
            <field name="code" type="int" value="9865" />
            <field name="name" type="string" value="Object Oriented Programming" />
            <field name="term" type="int" value="2" />
        </object>
    </object>
</object>

The root is an object element, which is the map of four entry objects. Each entry object has two children: the fisrt object represents the key, and the second object is the value associated with that key. The key is an object of type int, and the value is an object of type Course. The XML representation of a Course object has been explained in other sections.

De-serializing a map of Course objects back from XML

Since the map is not specific to Java or C#, we can use the load method of the Easy class de-seralize the map back from XML either to Java or C#. Note that WOX in Java does not require the Course class to have a default constructor; but WOX in C# does.

//Java
HashMap newMap = (HashMap)Easy.load(filename);

//C#
Hashtable newMap = (Hashtable)Easy.load(filename);

The map has been reconstructed and you can now iterate to display its elements.