[zappchance]

I asked your question to Claude but added a line specifying that I wanted more technical details. It actually included a line mentioning a cache but that's about it.

Here is Claude's response:

---

Strings in Java are implemented as objects of the String class. Under the hood, Java strings use the following internal representation:

- A char array to store the characters of the string

- An integer storing the length of the string

- Some other internal fields for synchronization and cache (since Java 5)

When a string is created in Java, a char array is allocated to store the characters of that string. The length integer is set to the actual length of the string.

For example, if you create a string like this:

  ```java
  String s = "hello";
  ```

Java will do the following:

- Allocate a char array of size 5 to store the 5 characters 'h', 'e', 'l', 'l', 'o'

- Set the length field to 5

- Initialize the char array with the string characters

So the internal representation in this case would be:

- A char[5] array initialized to {'h', 'e', 'l', 'l', 'o'}

- length = 5

When string operations like concatenation are performed, a new char array is allocated to store the resultant string and the length is updated accordingly. The String class then manages this char array and length field.

So in summary, Java strings use a char array and length field as their internal representation, and the String class encapsulates and manages this representation. The char array approach provides an efficient implementation for string operations in Java.

[fweimer]

That's fairly underwhelming? I don't think it's correct for any version of the JVM. Really old versions had offset/length fields, but never a length field on its own. (Back then, substring() didn't make full copies.) For mainline Java, since version 9, strings can use a byte[] to store characters if the string consists entirely of characters in the Latin-1 subset. String literal assignment does not allocate, and concatenation allocates a new String object and internal array.

What is being described is closer to a typical implementation of C++ std::string, without the small-strings optimization. And it's written rather convincingly.

[never_inline]

Yeah right nothing about hashcode either.

[zubairshaik]

I found Phind's response[0] to be the most detailed, but I cannot verify it's accuracy.

[0] https://www.phind.com/search?cache=d4888145-a89d-4a65-9eb8-8...

[pmoriarty]

Here is Claude+'s[1] response (note that's "Claude Plus", not just plain "Claude"). It mentioned hash code. I don't know Java, so can't comment on its accuracy.. but here it is, for what it's worth...

In Java, strings are represented by the String class. Under the hood, strings are represented by char arrays.

When a string is created in Java, it is stored in the heap memory. For example:

```java String s = "Hello"; ```

This will create a char array like this:

`['H', 'e', 'l', 'l', 'o']`

And the String s will point to this array.

The String class is immutable, meaning the char array cannot be changed once created. So when you do:

```java s = s + " World"; ```

This will actually create a new char array:

`['H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd']`

And s will now point to this new array. The old array will eventually be garbage collected.

Under the hood, String uses a char[] value field to store the characters. For example:

```java public final class String { private final char value[]; } ```

The array is marked final, meaning it cannot be changed after initialization. This is how String achieves immutability.

For small strings, the value array points to a char[s.length] array in the String object itself. For larger strings, value points to a separate char[] on the heap. This cutoff is determined by the MIN_VALUE_SIZE which is currently 15 characters.

The String class also has a hash field which caches the hash code for fast lookups in hash tables. There is also a serialVersionUID used for serialization.

Other details:

- String is backed by char, using UTF-16 encoding. - String pool is used to reuse similar strings and save memory. - Substring creates a new backing char array and shares it with the original string. - String is Comparable and has compareTo(), startsWith(), endsWith(), etc methods. - Escape sequences can be used in String literals, e.g. "\n" is newline. - Much more! Strings have many useful methods in the Java API.

Hope this helps provide lots of technical details on the internal representation of strings in Java! Let me know if you have any other questions.

[1] - https://poe.com/Claude%2B