Paper/src/main/java/net/minecraft/server/ItemMonsterEgg.java

package net.minecraft.server;

public class ItemMonsterEgg extends Item {

    public ItemMonsterEgg(int i) {
        super(i);
        this.a(true);
    }

    public boolean interactWith(ItemStack itemstack, EntityHuman entityhuman, World world, int i, int j, int k, int l) {
        if (world.isStatic || itemstack.getData() == 48 || itemstack.getData() == 49 || itemstack.getData() == 63) { // CraftBukkit
            return true;
        } else {
            int i1 = world.getTypeId(i, j, k);

            i += Facing.b[l];
            j += Facing.c[l];
            k += Facing.d[l];
            double d0 = 0.0D;

            if (l == 1 && i1 == Block.FENCE.id || i1 == Block.NETHER_FENCE.id) {
                d0 = 0.5D;
            }

            if (a(world, itemstack.getData(), (double) i + 0.5D, (double) j + d0, (double) k + 0.5D) && !entityhuman.abilities.canInstantlyBuild) {
                --itemstack.count;
            }

            return true;
        }
    }

    public static boolean a(World world, int i, double d0, double d1, double d2) {
        if (!EntityTypes.a.containsKey(Integer.valueOf(i))) {
            return false;
        } else {
            Entity entity = EntityTypes.a(i, world);

            if (entity != null && entity instanceof EntityLiving) { // CraftBukkit
                entity.setPositionRotation(d0, d1, d2, world.random.nextFloat() * 360.0F, 0.0F);
                world.addEntity(entity, org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.SPAWNER_EGG); // CraftBukkit
                ((EntityLiving) entity).ay();
            }

            return entity != null;
        }
    }
}