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Introduction. In Python, the string is an immutable object. You can use the '+' operator to append two strings to create a new string. There are various ways such as using join, format, string IO, and appending the strings with space.
The format() method of String class in Java 5 is the first choice. You just need to add "%03d" to add 3 leading zeros in an Integer. Formatting instruction to String starts with "%" and 0 is the character which is used in padding. By default left padding is used, 3 is the size and d is used to print integers.
+ "" evaluates to the number 0. This is because in order to apply the unary plus operator, "" is coerced to a number--the same as Number(""), which results in 0 if the string is empty or blank.
When you then "add" (+ or in this case +=) the number 0 to the string "abc", it is coerced to the string "0", resulting in "abc0".
From the spec:
A StringNumericLiteral that is empty or contains only white space is converted to +0.
As you can see in TypeScript (+ "") is a number (0):
from: http://xkr.us/articles/javascript/unary-add/
In JavaScript it is possible to use the + operator alone before a single element. This indicates a math operation and tries to convert the element to a number. If the conversion fails, it will evaluate to NaN. This is especially useful when one wants to convert a string to a number quickly, but can also be used on a select set of other types.
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