I want to check if there there isn't a block in specific coodinates

 

Block block = world.getBlock(x, y, z);

 

so have i to say

 

if (block == null).... or if(block == Blocks.air)....  ??

 

or is it the same?

Do instead

 

if (block == null || block.material == Material.air)

 

The first one checks to make sure the block isn't null (to avoid null reference errors) the second check checks to see if the block that is there is of the material air, because with mods there can be blocks that should be treated like air, but are not air.

 

(Gasses, technical lighting blocks, etc.)

I may be wrong, but in 1.7 and up it shouldn't really be possible to get a null reference to a block anymore (unless you are working with world gen and have the possibility of not-yet loaded chunks), since air blocks are real blocks now. That being said, it doesn't hurt to check

The whole point of getBlock is to return a block no matter what.

It can't be null, at worst it would already crash while trying to get the block.

It defaults to Blocks.air in most cases.

By the way, you have World#isAirBlock.

I want to check if there there isn't a block in specific coodinates

 

Block block = world.getBlock(x, y, z);

 

so have i to say

 

if (block == null).... or if(block == Blocks.air)....  ??

 

or is it the same?

 

if(block .isAir(world, x, y, z))

 

would check for air just remember if you pull the code form a specific block when your checking around that block to increase the coordinates as needed

 

if(block .isAir(world, x, y + 1, z)) would check if there's an air block above the Block