Difference between a string and an array of characters

Question

How are these declarations different from each other?

String s=\"MY PROFESSION\";
char c[]=\"MY PROFESSION\";

What about the memory allocation

Answer 1

How this declaration differentiate from each other?

Your first line produces a String instance. Your second line is simply invalid; perhaps you meant:

char[] c = {'M', 'Y', ' ', 'P', 'R', 'O', 'F', 'E', 'S', 'S', 'I', 'O', 'N'};

which creates char[] filled with those characters.

what about its memory allocation?

Storing a string as a String is slightly different memory-wise than storing it as a char[]. There are similarities though: both are objects, and have the usual object overhead.

However, a String holds a char[] internally, so naturally a String consumes more memory. Furthermore, String has 3 int fields (offset, count and hash) whereas char[] has the single int field length.

For example, storing "MY PROFESSION" as a String:

• 3 int fields: 12 bytes
• char[] field: 8 bytes
  • int field: 4 bytes
  • object overhead: 8 bytes
  • 13 characters: 26 bytes
• object overhead: 8 bytes

This comes out to about 66 bytes. I say "about" because some of this is dependent on the VM. The corresponding char[] of length 10 only consumes 38 bytes, as you can see. The memory difference here is quite negligible so you shouldn't worry about it (and just use a String!). It becomes even more insignificant the longer the string you are trying to store becomes.