Solidity allows a source file to import other source files. Here is an example to demonstrate this:
//This statement imports all global symbols from "filename" (and //symbols imported therein) to the current global scope. "filename" can //be an absolute or relative path. It can only be an HTTP URL //import "filename"; //creates a new global symbol symbolName whose members are all the //global symbols from "filename". import * as symbolName from "filename"; //creates new global symbols alias and symbol2 which reference symbol1 //and symbol2 from "filename", respectively. import {symbol1 as alias, symbol2} from "filename"; //this is equivalent to import * as symbolName from "filename";. import "filename" as symbolName;