main class:

OliveLeaves = new BasicBlock(Material.WOOD, MapColor.WOOD, "OliveLeaves");


public class BasicBlock extends Block {

	public BasicBlock(Material blockMaterialIn, MapColor blockMapColorIn, String blockName) {
		super(blockMaterialIn, blockMapColorIn);
		setCreativeTab(testmod.testtab);
        setRegistryName(blockName);
        setUnlocalizedName(blockName);
        GameRegistry.register(new ItemBlock(this).setRegistryName(this.getRegistryName()));
	}

    @SideOnly(Side.CLIENT)
    public void initModel() {
        ModelLoader.setCustomModelResourceLocation(Item.getItemFromBlock(this), 0, new ModelResourceLocation(getRegistryName(), "inventory"));
    }
}


json files:

blockstates > OliveLeaves.json:

{
    "variants": {
        "inventory": { "model": "testmod:OliveLeaves" }
    }
}

models > block > OliveLeaves.json

{
    "parent": "block/cube_all",
    "textures": {
        "all": "jerrysmod:blocks/OliveLeaves"
    }
}