NullPointer Exception

Alright, whenever I run the plugin on my bukkit server I get this error:

Code:

17:31:24 [SEVERE] Could not load 'plugins\volcan33.jar' in folder 'plugins'
org.bukkit.plugin.InvalidPluginException: java.lang.NullPointerException
        at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.j
ava:182)
        at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.
java:305)
        at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager
.java:230)
        at org.bukkit.craftbukkit.v1_6_R3.CraftServer.loadPlugins(CraftServer.ja
va:241)
        at org.bukkit.craftbukkit.v1_6_R3.CraftServer.<init>(CraftServer.java:21
9)
        at net.minecraft.server.v1_6_R3.PlayerList.<init>(PlayerList.java:56)
        at net.minecraft.server.v1_6_R3.DedicatedPlayerList.<init>(SourceFile:11
)
        at net.minecraft.server.v1_6_R3.DedicatedServer.init(DedicatedServer.jav
a:107)
        at net.minecraft.server.v1_6_R3.MinecraftServer.run(MinecraftServer.java
:393)
        at net.minecraft.server.v1_6_R3.ThreadServerApplication.run(SourceFile:5
83)
Caused by: java.lang.NullPointerException
        at com.gmail.mnoco8.Destruction.<init>(Destruction.java:30)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
 
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
 
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Sou
rce)
        at java.lang.reflect.Constructor.newInstance(Unknown Source)
        at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.j
ava:178)
        ... 9 more

Here is my code:

Code:java

package com.gmail.mnoco8;
 
import java.util.HashMap;
 
import java.util.Map;
import java.util.Random;
 
import org.bukkit.Location;
import org.bukkit.Material;
import org.bukkit.block.Block;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.block.BlockPlaceEvent;
import org.bukkit.plugin.java.JavaPlugin;
 
public class Destruction extends JavaPlugin implements Listener{
 
public void onEnable() {
getServer().getPluginManager().registerEvents(this, this); }
 
public void onDisable() {
 
}
 
Random rand = new Random();
Map<String, Location>
locations = new HashMap<String, Location>();
Location b = (Location) locations.get(Material.DRAGON_EGG).getBlock();
Location loc = locations.get(b);
Location loc2 = locations.put("Dragon_EGG", loc);
 
@EventHandler
public void onBlockPlace(BlockPlaceEvent e){
    Block block = e.getBlockPlaced();
    if(block.getType() == Material.DRAGON_EGG){
        loc2.add(loc);
    }
}
public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args)
{
    if (cmd.getName().equalsIgnoreCase("Volcano"));
    getServer().getWorld(label).spawnFallingBlock(loc, Material.LAVA, (byte) 0);
    return false;
}}

and here is my plugin.yml:

Code:

name: volcano
main: com.gmail.mnoco8.Destruction
version: 1.0
commands:
volcano:
  usage: volcano
    

 

Line 30 returns null

 

mnoco8 On line 29, you define a location hashmap of type <String, Location>, but you attempt to grab a value from it of the type Material on line 30. This gives a null value, because the HashMap has a key type of String, not Material. Fix that.

 

Maurdekye
I changed such, but

Code:java

Material b = locations.get(material.dragon_egg).getblock
 
 

seems to go quite funky, either resulting in changing material to block or material to location which present their own errors

 

mnoco8 At least repost your new code, or fix your original post so we can see what you've changed.

 

Maurdekye This is all I have changed:

Code:java

Map<Material,Location>
locations = new HashMap<Material, location>();
Material b = locations.get(Material.DRAGON_EGG).getBlock();
Location loc = locations.get(b);
Location loc2 = locations.put(b, loc);
 

 

mnoco8

This seems like a really easy problem because like Maurdekye was saying: You define a Hashmap on line 29, then you turn around and try to get data from the HashMap without ever populating the HashMap with data.

Hopefully this helps. Good luck!

 

Europia79 I am trying to add data, then call it so the .get i am trying to get the location of a block and then use it to put it in the hashmap and store it

 

mnoco8

I would
1. define the class
2. define the fields
3. initialize all the fields in the contructor
4. Use events gather data and populate your HashMap

Code:java

package com.gmail.mnoco8;
 
import java.util.HashMap;
 
import java.util.Map;
import java.util.Random;
import org.bukkit.Location;
import org.bukkit.Material;
import org.bukkit.block.Block;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.block.BlockPlaceEvent;
import org.bukkit.plugin.java.JavaPlugin;
 
public class Destruction extends JavaPlugin implements Listener {
 
Random rand;
Map<String, Location> locations;
 
/**
* Constructor
*/
public Destruction() {
rand = new Random();
locations = new HashMap<String, Location>();
}
 
public void onEnable() {
getServer().getPluginManager().registerEvents(this, this);
}
 
public void onDisable() {
}
 
@EventHandler
public void onBlockPlace(BlockPlaceEvent e){
Block block = e.getBlockPlaced();
if(block.getType() == Material.DRAGON_EGG){
locations.put(e.getPlayer().getName(), block.getLocation());
}
}
public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args)
{
if (cmd.getName().equalsIgnoreCase("Volcano"));
getServer().getWorld(label).spawnFallingBlock(loc, Material.LAVA, (byte) 0);
return false;
}}

 

Europia79 this presented more errors than usual, I just need to store the location, just get it simple as that then be able to call it later.

 

mnoco8

it works flawlessly for me:
I used the event to gather data and store it into the HashMap.
Then I used the "/gethashmap" command to access the data in it.

Code:java

package mc.euro.destruction;
 
import java.util.HashMap;
 
import java.util.Map;
import java.util.Random;
import org.bukkit.Location;
import org.bukkit.Material;
import org.bukkit.block.Block;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.block.BlockPlaceEvent;
import org.bukkit.plugin.java.JavaPlugin;
 
public class Destruction extends JavaPlugin implements Listener {
 
    Random rand;
    Map<String, Location> locations;
 
    /**
    * Constructor
    */
    public Destruction() {
        rand = new Random();
        locations = new HashMap<String, Location>();
 
    }
 
    @Override
    public void onEnable() {
        getServer().getPluginManager().registerEvents(this, this);
        getServer().getPluginCommand("getHashMap").setExecutor(this);
    }
 
    @Override
    public void onDisable() {
    }
 
    @EventHandler
    public void onBlockPlace(BlockPlaceEvent e) {
        e.getPlayer().sendMessage("Destruction event called.");
        Block block = e.getBlockPlaced();
        if (block.getType() == Material.DRAGON_EGG) {
            locations.put(e.getPlayer().getName(), block.getLocation());
        }
    }
 
    @Override
    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
        if (cmd.getName().equalsIgnoreCase("getHashMap") &&
                locations.containsKey(sender.getName())) {
            sender.sendMessage("" + locations.get(sender.getName()).toString());
        }
        return true;
    }
}