The first thing to learn is that every document should begin with beginDocument() and end with a call to endDocument().

reportGenerator.beginDocument();
reportGenerator.endDocument();
         

    A document must have a head, where some things are declared (for example new colors, page margins, etc). For now, let's just declare it without anything besides their normal behavior (it's mandatory to every document have a head explicitly declared).

reportGenerator.beginDocument();

reportGenerator.beginDocumentHead();
reportGenerator.endDocumentHead();

reportGenerator.endDocument();
         

    You are a clever person and are thinking: "if we must have a document head, we probably must have a document body". And I can say: "You are absolutely right!", all report elements that will be visible in the report final format are inserted inside the document's body. Thus, we must declare the body block.

reportGenerator.beginDocument();

reportGenerator.beginDocumentHead();
reportGenerator.endDocumentHead();

reportGenerator.beginDocumentBody();
reportGenerator.endDocumentBody();

reportGenerator.endDocument();
         

    "And if we have a body, the text to be visible should be inside that", you are thinking. Gosh, right again! is this tutorial really necessary?

reportGenerator.beginDocument();

reportGenerator.beginDocumentHead();
reportGenerator.endDocumentHead();

reportGenerator.beginDocumentBody();
reportGenerator.addText("Hello world!");
reportGenerator.endDocumentBody();

reportGenerator.endDocument();