Question

I am not able to understand the why such output when long variable with leading zero.

public class Test{
        public static void main(String[] args) {
             long var1=00123l;
             long var2=123l;
             System.out.println("Variable 1--->"+var1);
             System.out.println("Variable 2--->"+var2);
             System.out.println(var1==var2);
        }
    }

output:

Variable 1--->83
Variable 2--->123
false

Answer 1

The leading zero turns 00123l into an octal literal, and 123₈=83₁₀.

From the JLS:

An octal numeral consists of an ASCII digit 0 followed by one or more of the ASCII digits 0 through 7 interspersed with underscores, and can represent a positive, zero, or negative integer.

When you print the value, it gets printed in base-10, so you see 83.