“is-a”，“has-a”，“like-a”

1.“is-a” It's an inherited relationship , such as An equilateral triangle is a triangle , that , Triangle is the base class of equilateral triangle .
2.“has-a” It's an aggregated relationship ,, When A At the time of creation ,B Not necessarily create ; When A When they die ,B Not necessarily dead .
3.“like-a” It's a combinatorial relationship , When creating a A Object time , It will also create a B object ; When A When an object dies , As A Property of B Objects also die .