I want to know which block is under the Player .And if the BLock is identical to another block (selected before), do something. i tried something like this: (But I know it doesn't work at all). Thank you!
BlockPos PlayerIsStandingOn = player.getPosition().down();
Block PlayerIsStandingOnBlock = worldIn.getBlockState(PlayerIsStandingOn);
if (PlayerIsStandingOn == randomBlock) { }
You're close but getBlockState returns IBlockState not Block. You could do it like this:
BlockPos posBelow = player.getPosition().down();
IBlockState blockStateBelow = player.world.getBlockState(posBelow);
then you can either check if the block is a specific material like so, I think this is likely what you're after; this will return if the Material is not GROUND (dirt):
if(blockStateBelow.getMaterial() != Material.GROUND)
return;
//your logic here
Or you can do a comparison to check if two blocks are the same:
if(!Block.isEqualTo(blockStateBelow.getBlock(), <your other block>))
return;
//your logic here
And so on...
This answer was originally written for 1.12.2, it seems a few things have changed in 1.15.2
BlockPos posBelow = player.getPosition().down();
BlockState blockStateBelow = player.world.getBlockState(posBelow);
Block below = blockStateBelow.getBlock();
if(!below.equals(<your other block>))
return;