Getting a boolean from another class

Hi i'm creating a plugin that has gave me a few problems and the newest one is a java null pointer exception when i get the boolean from a diferent class my code :

Code:java

public class Teleport implements Listener {
 
private Arena a;
private Main plugin;
 
public Teleport(Main plugin) {
this.plugin = plugin;
}
 
@EventHandler
public void playertp(PlayerTeleportEvent e) {
World w = e.getTo().getWorld();
if (!w.equals(Bukkit.getWorld("Arenas"))) {
return;
} else {
if (a.on = false) {
Arena task1 = new Arena();
task1.setId(Bukkit.getServer().getScheduler()
.scheduleSyncRepeatingTask(plugin, task1, 0, 10));
} else {
Bukkit.broadcastMessage("COISO");
return;
}
}
if (!w.equals(Bukkit.getWorld("ArenasItem"))) {
return;
} else {
if (a.on = false) {
Arena task1 = new Arena();
task1.setId(Bukkit.getServer().getScheduler()
.scheduleSyncRepeatingTask(plugin, task1, 0, 10));
} else {
Bukkit.broadcastMessage("COISO");
return;
}
}
}
}

Code:java

public class Arena extends BukkitRunnable {
 
    private int id;
 
    public void setId(int id) {
        this.id = id;
    }
 
    public boolean on = false;
    World w = Bukkit.getWorld("Arenas");
    World w2 = Bukkit.getWorld("ArenasItem");
 
    @Override
    public void run() {
        for (Player p : w.getPlayers()) {
            for (Player p2 : w2.getPlayers()) {
                List<Player> pw = w.getPlayers();
                pw.add(p2);
                for (Player pp : pw) {
                    if(pp == null){
                        on = false;
                        Bukkit.getServer().getScheduler().cancelTask(id);
                        return;
                    }
                    double vida2 = pp.getHealth();
                    float vidap = (float) vida2 * 5;
                    String vida = ChatColor.RED.toString() + ChatColor.BOLD
                            + "HP: " + ChatColor.YELLOW.toString()
                            + ChatColor.BOLD + String.valueOf(vida2)
                            + ChatColor.RED.toString() + ChatColor.BOLD
                            + " Corações(20 = 10)";
                    BarAPI.setMessage(pp, vida);
                    BarAPI.setHealth(pp, vidap);
                    on = true;
                }
            }
        }
    }
}

 

Ever heard of static?
ALSO!
http://lmgtfy.com/?q=java, call a variable from a different class

try this:

Code:

    public static boolean on = false;

 

nuno1212sss

Code:java

private static boolean on = false;
 
public static boolean getOn() {
return on;
}

 

No no no NO.

Do not use static to substitute for lazy coding practices. You should be passing a reference of an object/primitive, not using static to access a member.

Some class:

Code:java

private boolean somefield = false;
private OtherClass clazz = new OtherClass();
 
void someMethod() {
    clazz.anotherMethod(somefield);
}

OtherClass:

Code:java

//...
public void anotherMethod(boolean value) {
    //work with value
}

In general, primitives are pass-by-value, and Objects are pass-by-reference.

More about passing instances: http://forums.bukkit.org/threads/using-a-string-in-different-classes.184140/#post-1916182
Why static is bad: http://stackoverflow.com/questions/7026507/why-are-static-variables-considered-evil

 

There is absolutely nothing wrong with using static variables, unless you use them wrong.

 

There is everything wrong with them. If you read the SO page I linked you would see why.

 

1Rogue I could use like constructors, but for what I want i'm not very clear on how to do because i want to check if the boolean is true or false, so do i like create a constructor and then return it true? Or can you explain a little better

 

Is your boolean a field? A common method is setting an accessor method:

Code:java

public class SomeClass {
 
    private boolean someValue = true;
 
    //...
 
    public boolean getSomeValue() {
        return this.someValue;
    }
 
}

As far as design patterns go, I usually structure mine in a way where you pass the main instance of your plugin to lower classes, and then you can always reference up. For example:

Main class:

Code:java

public class YourMain extends JavaPlugin {
 
    private SomeManager some;
    private AnotherClass another;
 
    public void onEnable() {
        this.some = new SomeManager(this);
 
        this.another = new AnotherClass(this);
    }
 
    public SomeManager getSomeManager() {
        return this.some;
    }
 
    public AnotherClass getAnotherClass() {
        return this.another;
    }
 
}

AnotherClass:

Code:java

public class AnotherClass {
 
    private final YourMain plugin;
    private boolean someValue = true;
 
    public AnotherClass(YourMain plugin) {
        this.plugin = plugin;
    }
 
    public boolean getSomeValue() {
        return this.someValue;
    }
 
}

This means that in our "SomeManager" class, we can then call the appropriate values:

SomeManager:

Code:java

public class SomeManager {
 
    private final YourMain plugin;
 
    public SomeManager(YourMain plugin) {
        this.plugin = plugin;
        if (this.plugin.getAnotherClass().getSomeValue()) {
            // value of "someValue" in "AnotherClass" instance is "true"
        } else {
            // the value is false
        }
    }
 
}

That's the gist of it, really.