A simple example of PistonExtendEvent and PistonRetractEvent

gistfile1.java

package net.minecraftforge.test;

import net.minecraftforge.common.MinecraftForge;
import net.minecraftforge.event.world.PistonEvent;
import net.minecraftforge.fml.common.Mod;
import net.minecraftforge.fml.common.Mod.EventHandler;
import net.minecraftforge.fml.common.event.FMLPreInitializationEvent;
import net.minecraftforge.fml.common.eventhandler.SubscribeEvent;

@Mod(modid = "pistonTest")
public class PistonTest 
{
    @EventHandler
    public void preInit(FMLPreInitializationEvent pre)
    {
        MinecraftForge.EVENT_BUS.register(this);
    }
    
    @SubscribeEvent
    public void pistonRetract(PistonEvent.PistonRetractEvent event)
    {
        event.setCanceled(true); /* The piston won't retract */
    }
    
    @SubscribeEvent
    public void pistonExtend(PistonEvent.PistonExtendEvent event)
    {
        event.setCanceled(true); /* The piston won't extend */
    }
}