Java read multiple objects from a file

Question

consider i have 2 different classes

public class A {

    String name;
    int A1;
    int A2;

}

and the other class is:

public class B {

    String B0;
    int B1;
    int B2;
}

and now i have a file which contains an integer, and several object of A and several of B

The file could be like

3
"Jim"; 1;2
"jef";3;5
"Peter";6;7
"aa";1;1
"bb";2;3
"cc";3;4

You can consider that the3 (in the beginning of the file)is the number of objects in class A and the rest are objects from class B.

The question is, how can i read and separate all objects from the file?

The main problem is that i don't know how can i read the first int from the file. what i did is

     InputStream inputFileStream = Main.class.getResourceAsStream("/inputFile.txt");
ObjectInputStream ois = new ObjectInputStream(inputStream);      
int i = ois.readInt();
     ois.close();

but it gives me an error:

Exception in thread "main" java.io.StreamCorruptedException: invalid stream header: 350A4261

Your question is a multi-step question, and the steps include 1) reading lines from a file, 2 using loops to read in the first x A types, then a while loop to read the remaining lines 3) converting each line to an A or B type. So.... where exactly are you stuck? Show what you've tried please. — Hovercraft Full Of Eels
– Hovercraft Full Of Eels, Commented Apr 3, 2016 at 19:35

Hovercraft Full Of Eels · Accepted Answer · 2016-04-03 19:52:32Z

0

The main problem is that i don't know how can i read the first int from the file.

You're reading a text file, not a data file, so don't use readInt(). Either use a BufferedReader, or my recommendation -- a Scanner object.

InputStream inputFileStream = Main.class.getResourceAsStream("/inputFile.txt");
Scanner scanner = new Scanner(inputFileStream);
int int = scanner.nextInt(); // get that first int
scanner.nextLine();   // go to the next line (swallow the end-of-line token)
//.....

Then use the same Scanner to read lines. Use

while (scanner.hasNextLine) {
    String line = scanner.nextLine();
    // here process the line into an A or B depending on the results of a counter variable
    // then increment the counter here
}

Note that your processing will likely use the split(...) method of String to split on ; and create an array of String with the items you need. You'll then need to parse the int related items via Integer.parseInt(...)

edited Apr 3, 2016 at 19:52

answered Apr 3, 2016 at 19:45

Hovercraft Full Of Eels

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3 Comments

Jeff Over a year ago

but when i go to the objects i have to change again my streaminput. right?

Hovercraft Full Of Eels Over a year ago

@KamyarParastesh: heck no. Use the same Scanner. See edit above. You will want to try something and see what happens.

Hovercraft Full Of Eels Over a year ago

@KamyarParastesh: Any further questions?

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