Understanding Java's String length() Method and Unicode Characters

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질문:

Why is it said that the length() method of String class doesn't return accurate results In Java? Is this statement correct? What do you think?

답변:

The statement that the length() method of the String class in Java doesn't return accurate results is not correct. The length() method in Java's String class accurately returns the number of characters in the string, as defined by the Unicode standard.

However, there are some nuances that might lead to confusion:

  1. Character Representation: In Java, a String is a sequence of char values, where each char is a 16-bit Unicode character. The length() method counts the number of char values in the string, not necessarily the number of visible characters. For example, certain characters, such as surrogate pairs (used to represent characters outside the Basic Multilingual Plane), may be represented by two char values but are visually perceived as a single character.

  2. Combining Characters: Some characters can be represented using multiple Unicode code points. For instance, an accented character can be represented as a base character followed by a combining character. The length() method will count each of these code points separately, which may not align with the visual representation of the string.

  3. Normalization: If a string contains characters that can be represented in multiple ways (e.g., an accented character can be represented as a single character or as a base character plus a combining character), the length() method will return different results depending on how the string is constructed.

In summary, while the length() method itself is accurate in terms of counting char values, it may not always align with the visual or logical representation of characters in certain cases involving complex Unicode characters. If you need to count the number of visually distinct characters, you may need to normalize the string and handle surrogate pairs and combining characters appropriately.