I'm going to try to make the dragon egg unbreakable (by pistons, etc.)

 

 

How do I add the method to the dragon egg class without editing the class?

I know very little about dragon eggs, so I'm not sure what you want. You need it to make it unmovable by pistons, blocking pistons from extending?

 

edit: if that's all you want, why would you need to add a method to the class?

 

Anyway, if all you need to do is make the block unmovable by pistons, just add this code somewhere in your mod (I'm thinking the PreInitializationEvent, but the InitializationEvent or some other may work as well)

 

Block dragonEggBlock = Block.dragonEgg;

try
{
     Material dragonEggMaterial = dragonEggBlock.blockMaterial;
     Class materialClass = Material.class;
     Field mobilityFlagField = materialClass.getDeclaredField("mobilityFlag");
     mobilityFlagField.setAccessible(true);

     mobilityFlagField.set(dragonEggMaterial, 2);
     mobilityFlagField.setAccessible(false);

}
catch (Exception e)
{
     System.err.println("An Exception was thrown while making Dragon Eggs unmovable: " + e.getClass() + "\n[[" + e.getMessage() + "]]"); 
     e.printStackTrace();
}

 

And if any exception is thrown let me know.

 

Note that if there's any other thing in the game that has the same Material as the DragonEggBlock (which is Material.dragonEgg), this other thing will also be unmovable. If that's not desirable, we need to rethink our strategy.

 

If you need to make the block unbreakable (like bedrock) it will also be unmovable by pistons but it's a lot easier to do. Ignore all the code above, and just invoke this method:

 

Block.dragonEgg.setBlockUnbreakable();

 

And finally, if you also need it to be undestructible by blasts, you also need this:

//I'll set it's blast resistance to the same of bedrock's, which is an exageration, but it doesn't make any difference, as long as it's a big number
Block.dragonEgg.setResistance(6000000.0F);

 

Although it was not clear to me what exactly did you want, I hope I gave you the information you needed.

 

edit2: there was an unecessary line on the code for changing the mobility flag. I spotted it and removed it.

edit3: of course, any mods that expect dragon eggs to have their vanilla behaviour will be incompatible with yours. If thats a concern, you should subclass dragon egg and make your own version where you can change whatever you want, but leaving the original dragon eggs where they should be and behaving as they should.