Java String 可以有多少个字符？
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How many characters can a Java String have?
提问by andandandand
I'm trying The Next Palindromeproblem from Sphere Online Judge (SPOJ) where I need to find a palindrome for a integer of up to a million digits. I thought about using Java's functions for reversing Strings, but would they allow for a String to be this long?
我正在尝试来自 Sphere Online Judge (SPOJ)的下一个回文问题，我需要在其中找到最多一百万位整数的回文。我想过使用 Java 的函数来反转字符串，但是它们会允许字符串这么长吗？
采纳答案by Bill the Lizard
You should be able to get a String of length
你应该能够得到一个长度的字符串
Integer.MAX_VALUEalways 2,147,483,647(231- 1)
(Defined by the Java specification, the maximum size of an array, which the String class uses for internal storage)
ORHalf your maximum heap size(since each character is two bytes) whichever is smaller.
Integer.MAX_VALUE始终为2,147,483,647(2 31- 1)
（由 Java 规范定义，数组的最大大小，String 类用于内部存储）
或Half your maximum heap size（因为每个字符是两个字节）以较小者为准。
回答by aperkins
I believe they can be up to 2^31-1 characters, as they are held by an internal array, and arrays are indexed by integers in Java.
我相信它们最多可以有 2^31-1 个字符，因为它们由内部数组保存，并且数组在 Java 中由整数索引。
回答by Mite Mitreski
Integer.MAX_VALUE is max size of string + depends of your memory size but the Problem on sphere's online judge you don't have to use those functions
Integer.MAX_VALUE 是字符串的最大大小 + 取决于您的内存大小，但 Sphere 在线判断问题您不必使用这些函数
回答by Thorbj?rn Ravn Andersen
Have you considered using BigDecimalinstead of Stringto hold your numbers?
您是否考虑过使用BigDecimal而不是String保存您的号码？
回答by Joe Plante
The heap part gets worse, my friends. UTF-16 isn't guaranteed to be limited to 16 bits and can expand to 32
堆部分变得更糟，我的朋友们。UTF-16 不保证限于 16 位，可以扩展到 32
回答by Peter Lawrey
While you can in theory Integer.MAX_VALUE characters, the JVM is limited in the size of the array it can use.
虽然理论上您可以使用 Integer.MAX_VALUE 字符，但 JVM 可以使用的数组大小受到限制。
public static void main(String... args) {
for (int i = 0; i < 4; i++) {
int len = Integer.MAX_VALUE - i;
try {
char[] ch = new char[len];
System.out.println("len: " + len + " OK");
} catch (Error e) {
System.out.println("len: " + len + " " + e);
}
}
}
on Oracle Java 8 update 92 prints
在 Oracle Java 8 update 92 上打印
len: 2147483647 java.lang.OutOfMemoryError: Requested array size exceeds VM limit
len: 2147483646 java.lang.OutOfMemoryError: Requested array size exceeds VM limit
len: 2147483645 OK
len: 2147483644 OK
Note: in Java 9, Strings will use byte[] which will mean that multi-byte characters will use more than one byte and reduce the maximum further. If you have all four byte code-points e.g. emojis, you will only get around 500 million characters
注意：在 Java 9 中，字符串将使用 byte[] 这意味着多字节字符将使用一个以上的字节并进一步减少最大值。如果您拥有所有四个字节的代码点，例如表情符号，您将只能获得大约 5 亿个字符
回答by Revin
Java9 uses byte[] to store String.value, so you can only get about 1GB Strings in Java9. Java8 on the other hand can have 2GB Strings.
Java9 使用 byte[] 来存储 String.value，所以在 Java9 中你只能得到大约 1GB 的字符串。另一方面，Java8 可以有 2GB 的字符串。
By character I mean "char"s, some character is not representable in BMP(like some of the emojis), so it will take more(currently 2) chars.
通过字符，我的意思是“字符”，某些字符在 BMP 中无法表示（如某些表情符号），因此需要更多（当前为 2 个）字符。
