My serialization class - warning

[Dawid Skrzypczynski]

Hi,
I wrote class to write and read serialization objects. I used generalized types but i had one warning whose i don't understand.
Code:

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;


class ObjectSerialization {
	public static <T> T readObject(String name) {
		T object = null;
		try {
			FileInputStream fileInputStream = new FileInputStream(name);
			ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);
			
			object = (T) objectInputStream.readObject();
			objectInputStream.close();
		}
		catch (IOException e) {
			e.printStackTrace();
		}
		catch (ClassNotFoundException e) {
			e.printStackTrace();
		}
		
		return object;
	}
	public static <T> void writeObject(String fileName, T obj) {
		try {
			FileOutputStream fileOutputStream = new FileOutputStream(fileName);
			ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream);
			
			objectOutputStream.writeObject(obj);
			objectOutputStream.close();
		}
		catch (FileNotFoundException e) {
			e.printStackTrace();
		}
		catch (IOException e) {
			e.printStackTrace();
		}
	}
}

Using:

import java.io.Serializable;


public class testowa {
	public static void main(String[] args) {
		
		String fileName = "data.bin";
		
		SerializationTest t = new SerializationTest(50, "Ala");
		ObjectSerialization.writeObject(fileName, t);
		
		SerializationTest xxx = ObjectSerialization.readObject(fileName);
		System.out.println(xxx._1);
		System.out.println(xxx._2);
	}
}
class SerializationTest implements Serializable {
	private static final long serialVersionUID = 1L;
	public int _1;
	public String _2;
	
	public SerializationTest(int x, String x2) {
		_1 = x;
		_2 = x2;
	

Program works correctly but in line 8 my Eclipse says: "Type safety: Unchecked cast from Object to T". What does this mean ?

[Rob Spoor]

Because of type erasure, the generic type is no longer available at runtime. That means that the JVM cannot check at that point if the cast is valid. If the object is not a T then you will get a ClassCastException, only at a different point in your code. It will be harder to trace back the cause to the unsafe cast.