We give a restriction formula on jumping numbers
which is a reformulation of Demailly–Ein–Lazarsfeld’s important restriction formula for multiplier ideal sheaves
and a generalization of Demailly–Kollár’s important restriction formula on complex singularity exponents,
and then we establish necessary conditions for the extremal case in the reformulated formula;
we pose the subadditivity property on the complex singularity exponents of plurisubharmonic functions
which is a generalization of Demailly–Kollár’s fundamental subadditivity property,
and then we establish necessary conditions for the extremal case in the generalization.
We also obtain two sharp relations on jumping numbers, introduce a new invariant of plurisubharmonic singularities and get its decreasing property for consecutive differences.