  In this paper, we firstly character the structures of symmetries $J$ such
that a projection $P$ is $J$-contractive. Then the minimal and maximal elements
of the symmetries $J$ with $P^{\ast}JP\leqslant J$(or $JP\geqslant0)$ are
given. Moreover, some formulas between $P_{(2I-P-P^{\ast})^{+}}$
$(P_{(2I-P-P^{\ast})^{-}})$ and $P_{(P+P^{\ast})^-}$ $(P_{(P+P^{\ast})^+})$ are
established.
