[bohh]

given the two classes:

class Document {
private String type = "dummy";
private byte [] data;
// enter get and set //

public classTestClass {
public static void main (String [] args) {
Document d = new PdfDocument ();
System.out.prinln (d.getType ());

I will write the code for the PdfDocument class so that Test Class will print "pdf" when run.

??????
HELP ME HEL ME

[MavenGradle]

What part isn't clear to you? It seems to be a rather simple exercise that should take no more than 2 minutes of your time.
Inheritance and system.out.println are your friends.

[bohh]

I did it and print pdf, but I don't use that part of the code from the data array part ... but it works.

the pdfDocument
public class PdfDocument extends Document {

public String getType() {//Override del metodo in Document
return "PDF";
}
}

e il test:

public class TestClass {

public static void main(String[] args) {
Document d = new PdfDocument();
System.out.println(d.getType());
}
}

class Document {
private String type = "dummy";//dummy viene sovrascitto dalla classe PdfDocument
private byte[] data;

public String getType() {
return type;
}

public void setType(String type) {
this.type = type;
}

public byte[] getData() {
return data;
}

public void setData(byte[] data) {
this.data = data;
}
}

[G.P.D.]

You can use the Apache Commons Java library :

Code

FileUtils.readFileToByteArray(File)

Where File is the object containing your pdf.
You can initialize it like so :

Code

File file = new File("/path/to/your/file.pdf");

So it'll look like :

Code

File myPdf = new File("/path/to/your/file.pdf");
byte[] pdfByteArray = FileUtils.readFileToByteArray(myPdf);

You'll maybe need to add a path variable to your Document object.

Whait.