JAVA 如何从一个表达式中读取包含数学运算符和数字的用户输入？

Question

I have an assignment that asks me to create a Basic calculator, by taking an input from the user in one expressions as in "4 - 1" or "5 + 3", and I need to check each number(1-9) and the operator (+,-,*,/) to see whether it is applicable. My question is how do I check whether the expression has a valid operator and spaces in between numbers and operator? (I'm a beginner in Java, and thank you in advance to whoever answers)

Answer 1

Though I am not entirely sure where you are stuck, this example expression may be your best friend:

    String exampleString = "Example String";
    char exampleChar = example.charAt(3);

This statement is true:

    exampleChar == 'm'

EDIT FOR ADDITIONS

To read the user input, you would need to read different types of characters. To read a number using the Scanner class, you would use .nextInt() or .nextDouble() to check for spaces and symbols, using .next() only reads till the next break. Please elaborate where you are getting stuck/where we can be more specific:)