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

User · Answer

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

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The heap part gets worse  my friends  UTF-16 isn t guaranteed to be limited to 16 bits and can expand to 32

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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

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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

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Have you considered using BigDecimal instead of String to hold your numbers

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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  lt  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 e g  emojis  you will only get around 500 million characters

User · Answer

You should be able to get a String of length    Integer MAX VALUE always 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  OR   Half your maximum heap size  since each character is two bytes  whichever is smaller

[java] How many characters can a Java String have?

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