java - Regular expression for arithmetic expression

Question

I,m trying to write a regex to check if the given string is like a + b, 2 + a + b, 3 + 6 * 9 + 6 * 5 + a * b, etc...

Only + and * operators.

I tried

if (str.matches("(\d|\w \+|\*){1,} \d|\w"))

Unfortunately it only handles cases like 3 * 7 ... (numeric * numeric).

Waiting for your answers, thanks for reading me.

Answer 1

Put * and + inside a character class.

str.matches("\w(?:\s[+*]\s\w)+");

DEMO