java.lang.NullPointerException - Probably a stupid error...

Hi Guys, im currently starting at making bukkit plugin so i just want to make a simple plugin but now all i have is this annoying error:

Code:

2011-03-12 12:26:29 [SEVERE] Could not load plugins/Citywars.jar in plugins: null
org.bukkit.plugin.InvalidPluginException
    at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:85)
    at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.java:129)
    at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager.java:94)
    at org.bukkit.craftbukkit.CraftServer.loadPlugins(CraftServer.java:55)
    at org.bukkit.craftbukkit.CraftServer.reload(CraftServer.java:195)
    at org.bukkit.command.SimpleCommandMap$ReloadCommand.execute(SimpleCommandMap.java:189)
    at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:77)
    at org.bukkit.craftbukkit.CraftServer.dispatchCommand(CraftServer.java:173)
    at net.minecraft.server.MinecraftServer.b(MinecraftServer.java:362)
    at net.minecraft.server.MinecraftServer.h(MinecraftServer.java:347)
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:253)
    at net.minecraft.server.ThreadServerApplication.run(SourceFile:366)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:532)
    at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:80)
    ... 11 more
Caused by: java.lang.NullPointerException
    at me.linkupdated.citywars.CitywarsBlockListener.<init>(CitywarsBlockListener.java:19)
    at me.linkupdated.citywars.Citywars.<init>(Citywars.java:18)
    ... 16 more

So if anyone could help me, it would be very apreciated.
Thanks

 

Well, hard to do with so little info.

You have a null pointer exception at line 19 of your file: CitywarsBlockListener.java.

I would suggest looking at that line and seeing if all variables are correctly initialised.

 

ok, i think i found my problem :

Code:

    public Connection connect() {
        try {
            Class.forName("com.mysql.jdbc.Driver");

            String url = "jdbc:mysql://localhost:3306/*****";
            String user = "*****";
            String passwd = "*****";

            Connection conn = DriverManager.getConnection(url, user, passwd);
            System.out.println("CITYWARS MYSQL CONNECTED-------------------------");
            return conn;
        } catch (Exception e) {
            System.out.println("CITYWARS MYSQL ERROR : " + e);
        }
        return null;
    }

when i call this function to connect to my bdd it crash, i call it in my BlockListener class

Code:

    public static Citywars plugin;
    Connection conn = plugin.connect();

So it seem im calling it wrong, im new to mysql in java, pretty much used to php anyone could help?
thanks!
[MERGETIME="1299971641"][/MERGETIME]
now it seemed to be fixed but each block destroyed i have this error :

Code:

2011-03-12 17:39:38 [SEVERE] Could not pass event BLOCK_BREAK to Citywars
java.lang.NullPointerException
        at me.linkupdated.citywars.CitywarsBlockListener.onBlockBreak(CitywarsBlockListener.java:41)
        at org.bukkit.plugin.java.JavaPluginLoader$31.execute(JavaPluginLoader.java:282)
        at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:59)
        at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:225)
        at net.minecraft.server.ItemInWorldManager.d(ItemInWorldManager.java:112)
        at net.minecraft.server.ItemInWorldManager.a(ItemInWorldManager.java:42)
        at net.minecraft.server.EntityPlayer.f_(EntityPlayer.java:72)
        at net.minecraft.server.World.a(World.java:1011)
        at net.minecraft.server.WorldServer.a(WorldServer.java:53)
        at net.minecraft.server.World.f(World.java:993)
        at net.minecraft.server.World.d(World.java:970)
        at net.minecraft.server.MinecraftServer.h(MinecraftServer.java:335)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:253)
        at net.minecraft.server.ThreadServerApplication.run(

 

Could you post your CitywarsBlockListener code?

 

here it is :

Code:

package me.linkupdated.citywars;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Date;
import java.text.DateFormat;
import java.text.SimpleDateFormat;

import org.bukkit.block.Block;
import org.bukkit.entity.Player;
import org.bukkit.event.block.BlockBreakEvent;
import org.bukkit.event.block.BlockListener;

public class CitywarsBlockListener extends BlockListener {

    public static Citywars plugin;
    Connection conn = this.connect();
    PreparedStatement stmt = null;

    public CitywarsBlockListener(Citywars instance) {
        plugin = instance;
    }

    public void onBlockBreak(BlockBreakEvent event) {
        Block block = event.getBlock();
        Player player = event.getPlayer();
        boolean PlayerFound = false;
        DateFormat format = new SimpleDateFormat("dd/MM/yyyy");
        /*
         * if(block.getType() == Material.TORCH && plugin.enabled(player)){
         * player.sendMessage(ChatColor.RED + "You Broke a torch ;)");
         * System.out.println(player.getDisplayName() + " Broke a torch!"); }
         * else if(block.getType() == Material.TORCH){
         * System.out.println(player.getDisplayName() + " Broke a torch! && " +
         * plugin.enabled(player)); }
         */
        try {
            ResultSet rs = stmt.executeQuery("SELECT * FROM citywars_plugin");

            while (rs.next()) {
                String PlayerName = rs.getString("citywars_plugin_player_name");
                if (PlayerName == player.getDisplayName()) {
                    PlayerFound = true;
                    try {
                        stmt.executeUpdate("UPDATE citywars_plugin SET citywars_plugin_block_broke='"+ block.getType() +"', citywars_plugin_time='"+ format.format(new Date()) +"' WHERE citywars_plugin_player_name='"+ player.getDisplayName() +"'");
                    } catch (SQLException e) {
                        System.out.println("CITYWARS MYSQL ERROR : " + e);
                    }
                }
            }
            if(PlayerFound == false){
                try {
                    stmt.executeUpdate("INSERT INTO citywars_plugin(citywars_plugin_player_name, citywars_plugin_time, citywars_plugin_block_broke) VALUE('"+ player.getDisplayName() +"', '"+ format.format(new Date()) +"', '"+ block.getType() +"')");
                } catch (SQLException e) {
                    System.out.println("CITYWARS MYSQL ERROR : " + e);
                }
            }

        } catch (SQLException e) {
            System.out.println("CITYWARS MYSQL ERROR : " + e);
        }
    }

    public Connection connect() {
        try {
            Class.forName("com.mysql.jdbc.Driver");

            String url = "jdbc:mysql://localhost:3306/*****";
            String user = "******";
            String passwd = "*******";

            Connection conn = DriverManager.getConnection(url, user, passwd);
            System.out.println("CITYWARS MYSQL CONNECTED-------------------------");
            return conn;
        } catch (Exception e) {
            System.out.println("CITYWARS MYSQL ERROR : " + e);
        }
        return null;
    }
}

and ill post my main class :

Code:

package me.linkupdated.citywars;

import java.sql.Connection;
import java.sql.DriverManager;
import java.util.ArrayList;
import java.util.HashMap;

import org.bukkit.block.Block;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.event.Event;
import org.bukkit.plugin.PluginManager;
import org.bukkit.plugin.java.JavaPlugin;

public class Citywars extends JavaPlugin {

    private final CitywarsBlockListener blockListener = new CitywarsBlockListener(this);
    public final HashMap<Player, ArrayList<Block>> citywarsUsers = new HashMap<Player, ArrayList<Block>>();

    /*
     * try { state = conn.createStatement();state.execute(
     * "UPDATE accounts SET accounts_online='Online' WHERE accounts_id='"
     * +User_Id+"'"); } catch (SQLException e) { e.printStackTrace(); }
     */

    public void onEnable() {
        PluginManager pm = getServer().getPluginManager();
        pm.registerEvent(Event.Type.BLOCK_BREAK, blockListener, Event.Priority.Normal, this);
        System.out.println("Citywars Started ----------------------------------------------");
    }

    public void onDisable() {
        System.out.println("Citywars Stopped -----------------------------------------------");
    }

    /*public boolean onCommand(CommandSender sender, Command cmd,
            String commandLabel, String[] args) {
        if (commandLabel.equalsIgnoreCase("Citywars")) {
            toggleCitywars((Player) sender);
            return true;
        }
        return false;
    }

    public void toggleCitywars(Player player) {
        if (enabled(player)) {
            this.citywarsUsers.remove(player);
            player.sendMessage("Citywars Disabled");
        } else {
            this.citywarsUsers.put(player, null);
            player.sendMessage("Citywars Enabled");
        }
    }

    public boolean enabled(Player player) {
        return this.citywarsUsers.containsKey(player);
    }*/

}

Hlaf of it is commented out, i suspect im really not good with bdd handling so i may need help about that if anyone could help me it would be greatly appreciated!

Thanks all.

 

Well it shouldn't be hard to fix :
PreparedStatement stmt = null;

You set it to null and never change it anywhere so it crashes when you call stmt.executeQuery

 

Hi again, And thank you crash i change the way i call my bdd connection and it worked, but now i have this whole other problem :

Code:

while (rs.next()) {
                String PlayerNameDb = rs.getString("citywars_plugin_player_name");
                String PlayerName = player.getDisplayName();
                if (PlayerNameDb == PlayerName) {
                    PlayerFound = true;
                    try {
                        stmt.executeUpdate("UPDATE citywars_plugin SET citywars_plugin_block_broke='"+ block.getType() +"', citywars_plugin_time='"+ format.format(new Date()) +"' WHERE citywars_plugin_player_name='"+ player.getDisplayName() +"'");
                    } catch (SQLException e) {
                        System.out.println("CITYWARS MYSQL ERROR : " + e);
                    }
                }
            }

i can't succeed to make : if (PlayerNameDb == PlayerName) { } The two vars are the same text but they wont pass as equals, i tought it was a var type error but now i put both to string any ideas?
[MERGETIME="1300201955"][/MERGETIME]
Or i will use regex as a final solution loll...

 

The '==' operator doesn't work for string comparison in java (although it does in some languages). You must use if(string1.equals(string2))

 

ohh i seee, thank you so much i didnt now, im kinda new to java. But in php im an advanced used lol...