So this line is okay to get the reader.

JsonReader reader = Json.createReader(new FileReader("Elements.JSON"));

Your problem is that JsonStructure is an interface that doesn't have the method getJsonArray, but JsonObject does.

Therefore, you need to be doing

JsonObject jsonst = reader.readObject();

And then you can use the methods of JsonObject like so

JsonArray elements = jsonst.getJsonArray("Elements");
for (int i = 0; i < elements.size(); i++) {
    JsonObject element = elements.getJsonObject(i);
    String name = element.getString("name");
}

Finally, when you are done with the reader, you need to close it.

reader.close();

It's included in Java EE 7 (not SE 7/8)

In javax.json package, both available types support emptiness checks because they both implement a java.collection interfaces:

JsonObject is-a java.util.Map<String, JsonValue>. As a result, one can check if such object contains any values by simply calling isEmpty() method.

JsonArray is-a java.util.List<JsonValue>. As a result, one - again - can check if the array is empty by calling isEmpty() method on it.

For traversing a tree of JsonStructures while marking all empty nodes, you can use this helper method:

boolean isValueEmpty(JsonValue v) {
  if (v == null) {
    return true; // or you may throw an exception, for example
  }
  switch(v.getValueType()) {
    case NULL:
      return true; // same as with Java null, we assume that it is Empty
    case ARRAY: 
      return ((JsonArray) v).isEmpty();
      // additionally, you can say that empty array is array with only empty elements
      // this means a check like this:
      // return ((JsonArray v).stream().allMatch(isValueEmpty); // recurse
    case OBJECT:
      return ((JsonObject v).isEmpty();
    case STRING:
      // optionally: if you want to treat '' as empty
      return ((JsonString v).getString().isEmpty();
    default:
      return false; // to my knowledge, no other Json types can be empty
  }
}

If using Maven, add this dependency to your pom.xml

<dependency>
    <groupId>javax.json</groupId>
    <artifactId>javax.json-api</artifactId>
    <version>1.0</version>
</dependency>

For Gradle, add this to your build.gradle

compile 'javax.json:javax.json-api:1.0'

include the following dependency in your "pom.xml" file.

<dependency>
    <groupId>com.googlecode.json-simple</groupId>
    <artifactId>json-simple</artifactId>
    <version>1.1.1</version>
</dependency>