If you do not like the String class name then you can use "typedef" to rename the String class.
In all the files where you do include String.h, insert these lines:
// If you do not like the class name String, then you can rename using typedef
typedef String StringSomethingElseIwant;
// Your remaing code may be like this ....
int main()
{
        StringSomethingElseIwant aa_renstr; 
        aa_renstr = "I renamed the String Class using typedef";
        .......etc...
}
If there is a conflict with another class-name having the same name, and you want to use both this class and conflicting class then you use this technique - in all the files where you do include String.h, insert these lines:
#define  String  String_somethingelse_which_I_want
#include "String.h"
#undef String
#include "ConflictingString.h"  // This also has String class...
// All your code goes here...
main()
{
        String_somethingelse_which_I_want aa;
        String bb; // This string class from conflicting string class
        aa = " some sample string";
        bb = " another string abraka-dabraka";
        .......
}