Strange behaviour after using ObjectInputStream

Question

I'm trying to implement a save/load function for a game I'm developing. Basically, I have a main class which performs all the rendering and updates a game state object (the game state object holds the player, enemies, and their respective positions, speeds, etc). So I thought I would just save the game state object to a file usingObjectOutputStream and load with ObjectInputStream. The saving/loading seems to work fine, until the point where I perform an if-statement on a String field in the player class. I have remade the code as short possible to reproduce the strange behaviour.

The player class:

import java.io.Serializable;

public class Player implements Serializable
{
    /**
     * 
     */
    private static final long serialVersionUID = -5933597609049497854L;
    private String type;

    public Player()
    {
        type = "evil";
    }

    public String getType()
    {
        return type;
    }


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

The Main class:

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

public class Main
{
    private Player player;

    public Main()
    {
        player = new Player();

        System.out.println("player.getType(): ");
        System.out.println(player.getType());
        System.out.println("player.getType() == evil: ");
        System.out.println(player.getType() == "evil");

        saveGame();

        loadGame();

        System.out.println("player.getType(): ");
        System.out.println(player.getType());
        System.out.println("player.getType() == evil: ");
        System.out.println(player.getType() == "evil");
    }

    public static void main(String[] Args)
    {
        new Main();
    }

    private void saveGame()
    {
        try
        {
            FileOutputStream out = new FileOutputStream("save");

            ObjectOutputStream objectOut = new ObjectOutputStream(out);

            objectOut.writeObject(player);

            objectOut.close();

        } catch (Exception e)
        {
            e.printStackTrace();
        }
    }

    private void loadGame()
    {
        try
        {

            FileInputStream fin = new FileInputStream("save");

            ObjectInputStream objectIn = new ObjectInputStream(fin);

            player = null;

            player = (Player) objectIn.readObject();

            objectIn.close();

        } catch (Exception e)
        {
            e.printStackTrace();
        }
    }
}

I recieve the following output from the program:

player.getType():
evil
player.getType() == evil:
true
player.getType():
evil
player.getType() == evil:
false

Why is the field type not recognized as "evil"?

`player.getType() == "evil"` Use the equals method when comparing String objects. — copeg, May 05 '15 at 23:49
`==` can't be used to compare strings (or objects in general) - at least not with the output that you expect. use `equals` instead. Apart from that do some research before asking -.- — , May 05 '15 at 23:50

score 0 · Accepted Answer · answered May 05 '15 at 23:51

0

Because Object equality is tested with .equals. If you use == you are testing reference equality, and two instances of equivalent value may (and with Serialization will) have different references. You need something like

player.getType().equals("evil")

answered May 05 '15 at 23:51

Elliott Frisch

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Strange behaviour after using ObjectInputStream

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