How To Find Duplicate Characters In A String In Java ? Here will discuss about how to find How To Find Duplicate Characters In A String Java . It is very easy and tricky question .Most of the interviewers will ask this question . For example, if given input to your program is “Java”, it should print all duplicates characters, i.e. characters appear more than once in String and their count e.g. a = 2 because character ‘a’ has appeared twice in String “Java”. This is also a very popular coding question on the various level of Java interviews and written test, where you need to write code. On difficulty level, this question is at par with prime numbers or Fibonacci series. I personally like this exercise because it gives beginners an opportunity to familiar with the concept of Map data structure, which allows you store mappings in the form of key and value. Since Map is heavily used in any enterprise Java application, good knowledge of this data structure is highly desirable among any level of Java programmers.
You can do Java sort string characters alphabetically using Arrays.sort, if you put the characters into an array first. (It must be an array of Character objects rather than char primitives, in order to use a custom case-insensitive comparator .
Sorting as a task has a lower bound of O(n*logn), with n being the number of elements to sort. What this means is that if you are using a single loop with simple operations, it will not be guaranteed to sort correctly. A key element in sorting is deciding what you are sorting by. In this case its alphabetically, which, if you convert each character to a char, equates to sorting in ascending order, since a char is actually just a number that the machine maps to the character, with ‘a’ < ‘b’. The only gotcha to look out for is mixed case, since ‘z’ < ‘A’. To get around, this, you can use str.tolower().