Can only use snippet code twice before getting errors

Question

I've been using this code to read private fields in Java to later pass them into Maps for bukkit.

Field FieldF = net.minecraft.server.v1_9_R2.EntityTypes.class.getDeclaredField("F");
    FieldF.setAccessible(true);
    Object valueF = FieldF.get("valueF");

However, when I do this try or more times I get Errors.

Unhandled exception type NoSuchFieldException

Once I add throws declaration throws NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException I get another error:

After I add throws NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException

How can I use the first code without any errors? I can only use it twice before I get the error.

Full Code:

package io.github.rookietec9.EnderPlugin.Entities;

import java.lang.reflect.Field;
import java.util.Map;

import org.bukkit.Location;
import org.bukkit.World;

import net.minecraft.server.v1_9_R2.Entity;

public enum CustomBase {

// NAME("Entity name", Entity ID, yourcustomclass.class)

CUSTOM_SKELETON("Skeleton", 54, CustomSkeleton.class); // You can add as
                                                        // many as you want.

private CustomBase(String name, int id, Class<? extends Entity> custom) {
    addToMaps(custom, name, id);
}

public static void spawnEntity(Entity entity, Location loc) {
    Location Loc = new Location((World) entity.getWorld(), loc.getX(), loc.getY(), loc.getZ(), loc.getYaw(),
            loc.getPitch());
    spawnEntity(entity, Loc);
}

@SuppressWarnings({ "rawtypes", "unchecked" })
private static void addToMaps(Class clazz, String name, int id) {
    // Remove the lines with // in front of them if you want to override
    // default entities (You'd have to remove the default entity from the
    // map first though).
    Field FieldF = net.minecraft.server.v1_9_R2.EntityTypes.class.getDeclaredField("F");
    FieldF.setAccessible(true);
    Object valueF = FieldF.get("valueF");
    Field FieldC = net.minecraft.server.v1_9_R2.EntityTypes.class.getDeclaredField("D");
    FieldC.setAccessible(true);
    Object valueC = FieldC.get("valueC");
    Field FieldD = net.minecraft.server.v1_9_R2.EntityTypes.class.getDeclaredField("C");
    FieldD.setAccessible(true);
    Object valueD = FieldD.get("valueD");



    ((Map) valueC).put(name, clazz);
    ((Map) valueD).put(clazz, name);
    ((Map) valueF).put(clazz, Integer.valueOf(id));
    // ((Map)getPrivateField("e",
    // net.minecraft.server.v1_7_R4.EntityTypes.class,
    // null)).put(Integer.valueOf(id), clazz);
    // ((Map)getPrivateField("g",
    // net.minecraft.server.v1_7_R4.EntityTypes.class, null)).put(name,
    // Integer.valueOf(id));
}

}

score 1 · Accepted Answer · answered Jun 24 '16 at 16:06

First, learn a bit of Java. https://docs.oracle.com/javase/tutorial/essential/exceptions/

Use try/catch blocks instead of throws declarations in addToMaps()

An example:

 Class clazz = null;
 try{
  clazz = Class.forName("YourClass");
 } catch (ClassNotFoundException e){
  e.printStackTrace();
 }

score 1 · Answer 2 · answered Jun 24 '16 at 16:19

Firstly your reflection usage isn't exactly correct. This is how it should be set up:

// field.get(Object reference) = gets the field value of the given instance
Object ref = MyApplication.getExample();
Field f = Example.class.getField("exampleField");
f.setAccessible(true);
Object val = f.get(ref);

// If the field is static you don't need a reference
Field staticField = Example.class.getField("staticField");
staticField.setAccessible(true);
Object val = staticField.get(null);

As for syntax, you are calling methods that throw exceptions. You will need to handle them with a try-catch. If your constructor throws exceptions you won't be able to create those enum constants.

Unrelated to errors, capitalized variable names aren't smiled upon. Nor are capitalized package names.

Can only use snippet code twice before getting errors

2 Answers2