Why is the output of this code 7 and not 1001?

Question

String a = “101”;
String b = “010”;
int a1 = Integer.parseInt(a,2);
int b1 = Integer.parseInt(b,2);
int sum = a1 + b1;
System.out.print(sum);

I’m confused with how .parseInt() works in this code.

Answer 1

in parenthesis (a, 2) and (b,2)means that number in binary.
a1 = 5
b1 = 2
a1 + b1 = 7

Answer 2

Integer.parseInt(a,2) returns the decimal value of a binary number (base 2 to base 10).

"101" (binary) -> 5 (decimal)
"010" (binary) -> 2 (decimal)

5 + 2 == 7.