java - long value with 0 on left

Question

Why this behavior happens?

long value = 123450;
System.out.println("value: " + value); 

value: 123450

 

long value = 0123450;
//           ^
System.out.println("value: " + value); 

value: 42792

What is this 42792?

Answer 1

Why this behavior happens?

Just as literals starting with 0x are treated as hexadecimal numbers (base 16), literals starting with a 0 are treated as octal numbers, i.e., numbers in base 8.

(Try writing 0789, and you'll see that the compiler will complain.)

What is this 42792?

The number 123450 in base 8 represents the number

1×8⁵ + 2×8⁴ + 3×8³ + 4×8² + 5×8¹ + 0×8⁰ = 42792