Why Do Leading Zeros in Java Integer Literals Change Their Value?

Interpretation of Integer Literals with Leading Zeroes

Integer literals with leading zeroes can behave unexpectedly in Java, exhibiting a different numerical value from their counterparts without leading zeroes. This behavior stems from the interpretation of leading zeroes as a base prefix.

When a numeric literal is prefixed with a zero, it is interpreted as an octal (base-8) number. This is because in octal notation, numbers can range from 0 to 7. Thus, "0123" represents the octal number 123.

To convert this octal number to its decimal equivalent, each digit is multiplied by its corresponding power of 8 and the results are summed. For "0123," this calculation is:

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

Therefore, the code "System.out.println(0123)" prints 83.

In contrast, "123" without a leading zero is interpreted as a decimal number. The decimal number 123 is simply the sum of its digits (1 2 3), which is 123. Thus, "System.out.println(123)" prints 123.

Avoid Misinterpretation

To avoid the unexpected behavior of leading zeroes in integer literals, it is recommended to always start decimal numbers with a non-zero digit. If a literal is intended to be expressed in base-10, it should not have a leading zero.

Alternative Base Notations

While octal is no longer commonly used, Java does provide a way to specify hexadecimal (base-16) numbers using the "0x" prefix. For example, "0x123" represents the hexadecimal number 123, which is equivalent to the decimal number 291.

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