Your main focus is to implement the shunting-yard algorithm as described here: https://en.wikipedia.org/wiki/Shunting-yard_algorithm

You most likely should not bother with the ^(exponential) operator.

Start with a String of text tokens, each of which can be +,=,/,*,(,), or a number representing an infix expression.

Use the shunting yard algorithm to evaluate the expression. If your input line is

String theLine;

Then, you should be able to do the expressions one by one by doing something similar to this:

StringTokenizer(theLine, "+-/*() ", true);

The final true tells the tokenizer to create tokens of the various separators, so if you tokenize

theLine = "(10.0 + 12.0)/4.0 + 3.0";

your tokens will be something like

( 10.0

+

12.0 ) 4.0

+

3.0

You will need to get rid of any tokens consisting of only blank space.