How many characters can a Java String have?

Question

I'm trying The Next Palindrome problem 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?

Answer 1

You should be able to get a String of length

1. Integer.MAX_VALUE always 2,147,483,647 (2 ³¹ - 1)
   (Defined by the Java specification, the maximum size of an array, which the String class uses for internal storage)
   OR

2. Half your maximum heap size (since each character is two bytes) whichever is smaller .

Answer 2

我相信它们最多可以包含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。

Answer 3

While you can in theory Integer.MAX_VALUE characters, the JVM is limited in the size of the array it can use.

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

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 eg emojis, you will only get around 500 million characters

Answer 4

您是否考虑过使用BigDecimal而不是String来保存数字？

Answer 5

Integer.MAX_VALUE是字符串的最大大小+取决于您的内存大小，但是球的在线问题认为您不必使用这些函数

Answer 6

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.

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.

Answer 7

The heap part gets worse, my friends. UTF-16 isn't guaranteed to be limited to 16 bits and can expand to 32