10 Examples of Joining String in Java 8 - StringJoiner and String.join()

It's quite common in day to day programming to join Strings e.g. if you have an array or List of String let's say {Sony, Apple, Google} and you want to join them by comma to produce another String "Sony, Apple, Google", there is not an easy way to do it in Java. You need to iterate through array or list and then use a StringBuilder to append a comma after each element and finally to remove the last comma because you don't want a comma after the last element. A JavaScript-like Array.join() method or join() method of Android's TextUtils class is what you need in this situation, but you won't find any of such method on String, StringBuffer, StringBuilder, Arrays, or Collections class until Java 8. Now, you have a class called StringJoiner which allows you to join multiple String by a delimiter.

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How to Remove Duplicate Characters from String in Java

This week's coding exercise is to remove duplicate characters from String in Java. For example, if given String is "aaaaaa" then output should be "a", because rest of  the "a" are duplicates. Similarly, if the input is "abcd" then output should also be "abcd" because there is no duplicate character in this String.  By the way, you can not use any third-party library or Java API method to solve this problem, you need to develop your own logic or algorithm and then write code to implement that algorithm. This is one of the interesting problems from Java coding interviews and you can use this program to weed out Java programmers who cannot write code. This problem is much better than Fizzbuzz because it requires more logic and coding than solving Fizzbuzz.

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How to Convert an Array to Comma Separated String in Java

The simplest way to convert an array to comma separated String is to create a StringBuilder, iterate through the array, and add each element of the array into StringBuilder after appending comma. You just need Java 1.5 for that, even if you are not running on Java 5, you can use StringBuffer in place of StringBuilder. The joining of String has got even easier in JDK 8, where you have got the join() method right in the String class itself. The join() method takes a delimiter and a source, which can be array or collection and returns a String where each element is joined by a delimiter. If you want to create a CSV string, just pass comma as a delimiter. Btw, these two methods are not the only way to create a comma separated String from an array, you can also use Apache Commons or Spring framework's utility class to do the same.

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How to Reverse a String in place in Java - Example

It's possible to reverse a String in place by using a StringBuilder. Since String is Immutable in Java, it's not possible to reverse the same String, but you can minimize the number of intermediate String objects by using StringBuilder or StringBuffer, which are mutable. The algorithm to reverse the String in place is similar to the algorithm we have used earlier to reverse an array in place. You need to traverse the String from one end, swapping characters at another end until you reach the middle of the String. At the point characters in your String is reversed. This algorithm only requires one extra character of memory to facilitate the swapping of characters. The time complexity of this algorithm is O(n/2) i.e. O(n) where n is the length of String.

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How to Remove First and Last Character of String in Java - Example Tutorial

You can use the substring() method of java.lang.String class to remove the first or last character of String in Java. The substring() method is overloaded and provides a couple of versions which allows you to remove a character from any position in Java. Alternatively, you can convert String to StringBuffer or StringBuilder and then use its remove() method to remove the first or last character. Both StringBuffer and StringBuilder provides a convenient deleteCharAt(int index) method which removes a character from the corresponding index. You can use this method to remove both first and last character from String in Java. In the last article, I have showed you how to get the first and last character from String and today I will teach you how to remove the first and last character of String in Java. Let's see a couple of examples and how you can use these two techniques to solve this problem.

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2 ways to Split String with Dot (.) in Java using Regular Expression

You can use the split() method of java.lang.String class to split a String based on the dot. Unlike comma, colon, or whitespace, a dot is not a common delimiter to join String, and that's why beginner often struggles to split a String by dot. One more reason for this struggle is the dot being a special character in the regular expression. If you want to split String on the dot you need to escape dot as \\. instead of just passing "." to  the split() method. Alternatively, you can also use the regular expression [.] to split the String by a dot in Java. The dot is mostly used to get the file extension as shown in our example. The logic and method are exactly same as earlier examples of split string on space and split the string on a comma, the only difference is the regular expression. Once you know how to write the regular expression, all these examples will be same for you. Java's regular expression is inspired by Perl.

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How to remove all special characters from String in Java

You can use regular expression and replaceAll() method of java.lang.String class to remove all special characters from String. A special character is nothing but characters like ! #, % etc. Precisely, you need to define what is a special character for you. Once you define that you can use a regular expression to replace those character with empty String, which is equivalent to removing all special characters from String. For example, suppose, your String contains some special characters e.g. "Awesome!!!" and you want to remove those !!! to reduce some excitement, you can use replaceAll("!", "") to get rid of all exclamation mark from String. Similarly, if you String contains many special characters, you can remove all of them by just picking alphanumeric characters e.g. replaceAll("[^a-zA-Z0-9_-]", ""), which will replace anything with empty String except a to z, A to Z, 0 to 9,_ and dash. Let's see couple fo examples to remove all special characters from String in Java.

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How to get first and last character of String in Java - Example

You can get the first and last character of a String using charAt() method in Java. This method accepts an integer index and returns the corresponding character from String. Since Java String is backed by an array, their index is also zero-based, which means the first character resides at index zero and the last character is at index, length-1, where length is the number of characters in the String. You can get the length of String by calling the length() method. The charAt() method is not defined on java.lang.String class, but on its super interface java.lang.CharSequence, hence it will also work for StringBuffer and StringBuilder. This method returns the char value at the specified index. An index ranges from 0 to length() - 1. The first char value of the sequence is at index 0, the next at index 1, and so on, as for array indexing. If the char value specified by the index is a surrogate, the surrogate value is returned.

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How to check if String is not null and empty in Java?

In Java, since null and empty are two different concept, it's a little bit tricky for beginners to check if a String is both not null and not empty. A String reference variable points to null if it has not been initialized and an empty String is a String without any character or a String of zero length. Remember, a String with just whitespace may not be considered as empty String by one program but considered as empty String by others, so, depending upon your situation, you can include the logic to check for that as well. A String with just white space is also referred as blank String in java. In this tutorial, I will teach you a couple of right ways to test if a String is not null and not empty in Java.

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