Answer 1

there are third-party libraries, e.g. mXparser
https://en.wikipedia.org/wiki/Mxparser#User-defined_functions[3]
http://mathparser.org/api/org/mariuszgromada/math/mxparser/Function.html

Function f = new Function("f(x, y) = sin(x)+cos(y)");
Expression e = new Expression("f(1,2)", f);
double v = e.calculate();

Answer 2

There are no predefined functions in java to do what you are asking for. You have to write the code but it will be specific for a single equation.

For eg- Like you showed.
There can be three operands, each separated by an operator. It could be any legal operator and the input should be a string type.