Why Does `0123` Print `83` in Java?

Leading Zeroes Confuse Integer Interpretation

When dealing with integer literals, the presence of leading zeroes can have unexpected consequences. Consider the following code:

System.out.println(0123); // prints 83
System.out.println(123);  // prints 123

Why does the first line print 83 instead of 123? The key lies in the leading zero.

Octal Interpretation

A leading zero in an integer literal indicates that the number is expressed in octal (base-8). To convert an octal number to decimal, multiply each digit from right to left by the appropriate power of 8 and sum the results.

In the case of 0123, we have:

(1 * 8 * 8) + (2 * 8) + (3) = 83

Therefore, 0123 is interpreted as the decimal value 83.

Why No Octal Floats?

Curiously, Java does not allow octal floating-point literals, so this behavior only applies to integers.

Best Practice

To avoid confusion, it is generally recommended to avoid using leading zeroes in integer literals unless you specifically intend the number to be interpreted as octal.

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