Having trouble getting readAllBytes() method to work

Other students in my class have gotten this code to work, but I get an error. I am trying to use the readAllBytes() method for an assignment and I can't get it to work. My teacher there is another way he intended it to work using That method is not defined for DataInputStream.
Take a look at the read(byte[]) method and the first integer in the datastream shows how large the byte Array is. Either way will work, I just am getting an error on line 39, and if I delete "import java.io.DataInputStream;" it fixes that error but I get an error on line 31 instead. Any help would be much appreciated enter image description here

package edu.ics211.h03;
import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.io.InputStream;
/**
* Represents a ReadFile.
*
* @author Constantine Peros
*/
public class ReadFile implements IReadFile {
/**
* Creates a New ReadFile.
*/
public ReadFile() {
// TODO Auto-generated constructor stub
}
@Override
public String readFile(String fileName) throws IOException {
// Create a FileInputStream from the file name
// Create a DataInputStream from the FileInputStream
DataInputStream data = new DataInputStream(new FileInputStream(fileName));
// Read the number of bytes using readInt
int size = data.readInt();
// Read the encoding using readByte
byte encoding = data.readByte();
// Create a byte array number of bytes long
byte[] byteArray = new byte[size];
// Fill the byte array
byteArray = data.readAllBytes();
// Close my inputs
data.close();
// Switch the encoding or use if statements
switch (encoding) {
case 1:
return new String(byteArray, StandardCharsets.US_ASCII);
break;
case 2:
return new String(byteArray, StandardCharsets.UTF_16LE);     
break;
case 3:
return new String(byteArray, StandardCharsets.UTF_8);     
break;
case 4:
return new String(byteArray, StandardCharsets.UTF_16);     
break;
default:
return null;
}
}
}

Seems to me that all you need to do is replace this line of the code

byteArray = data.readAllBytes();

with this line

data.read(byteArray);

Here is the entire method.

public String readFile(String fileName) throws IOException {
    // Create a FileInputStream from the file name
    // Create a DataInputStream from the FileInputStream
    DataInputStream data = new DataInputStream(new FileInputStream(fileName));
    // Read the number of bytes using readInt
    int size = data.readInt();
    // Read the encoding using readByte
    byte encoding = data.readByte();
    // Create a byte array number of bytes long
    byte[] byteArray = new byte[size];
    // Fill the byte array
    data.read(byteArray);
//  byteArray = data.readAllBytes();
    // Close my inputs
    data.close();
    // Switch the encoding or use if statements
    switch (encoding) {
        case 1:
            return new String(byteArray, StandardCharsets.US_ASCII);
        case 2:
            return new String(byteArray, StandardCharsets.UTF_16LE);     
        case 3:
            return new String(byteArray, StandardCharsets.UTF_8);     
        case 4:
            return new String(byteArray, StandardCharsets.UTF_16);     
        default:
            return null;
    }
}