Java从字符串中提取多个值

Question

As part of a calulator program I am writing, I am required to have the user input all the parameters in one string and I need to extract the corresponding values from it.

For example the user enters "3 5 *" he'll get "15" back.

So the program I need to write will take '3' and assign that to double input1 , '5' to double input2 , and '*' to char operator . How do I get java to assign parts of a string to different members.

I was thinking of maybe splitting the user's string into multiple strings and parsing the values out but I don't know how effective that would be. Thanks in advance.

Answer 1

You will need to consider the order of operations if you have more then one operation. IE (3 4 +) 3 *. A common method for this would be to use a stack. Push the values onto the stack and perform the operation on the values you pop following the operation itself. For parsing simply split on the space ' '. However if you have more complex expressions consider a post order traversal, or stack implementation.

Answer 2

This question has already been answered here: Evaluating a math expression given in string form

I gave a very simple breakdown in my answer here as well: Calculating String-inputed numerical expressions?

Answer 3

You can use the StringTokenizer to split the string wherever it finds a space.

String s = "3 5 *"; StringTokenizer st = new StringTokenizer(s);

You can check if there are more tokens via st.hasMoreTokens(). You can use the token aka string via st.nextToken() (it returns a string).

You can also cast each "string" such as the "3" into a double via: String firstNumString = "3"; Double first = Double.parseDouble(firstNumString);

This results in the Double variable 'first' containing the number 3.