12 Methods to Convert a List to String in Java
Looking to convert List to String in Java? Let’s have a look at how to convert a Java Collections List of elements to a String in Java. In this post, we have talked about these best 12 methods of convert list string in java, you can learn and also implement it easily.
To Convert a list to string in java, You can do by,
1. Using toString()
2. List Of Object To String
3. Join Method(StringUtils)
4. Stream Collectors
5. Comma Separator(delimiter)
6. Convert Character List To String
7. With Double Quotes
8. Sort Method
9. toJSON Method
10. The method in Java 8
11. ReplaceAll Method
12. LinkList to String
Introduction to Convert List to String in Java
Basically List in Java is an ordered collection or a default sequence.
List accepts duplicate elements unlike Map doesn’t accept duplicate values and also holds the object in key-value pairs.
We can print the contents of a List element in a readable form while debugging the code, which is helpful.
List interface and String class were part of Java object-oriented programming API.
We can add any type of Java object to a List. If the List does not type, then using Java Generics we can apply objects of various types in the same List.
Typically we will enclose the generic type in square brackets.
Using toString()
From the below Java program, let’s see how to convert Java list to string array using the toString method.
We are passing an integer argument(number) to create a java string array using the Java Arrays asList() method.
In other words, we are passing a list of integers as an array to list.
As per the output code above, we can see a list of array values printed as an array of strings or string array in java.
This way of implementation uses the inbuilt toString() method within the List.
Here Integer Java generics type has an internal implementation of the toString() method.
In the above example, we used Arrays.asList to create an array in java in an optimal manner.
But we can also use standard ArrayList in java and can add the values using the list.add() method or addAll method.
Also, we can convert from traditional ArrayList to String Array using ArrayList Class.
Interview Question 1 -> Primitive Types in Java:
boolean, byte, char, short, int, long, float, and double are the primitive types in Java API.
List of Object to String
Let’s see how Object toString() method works as per below java program class.
Here the custom toString() function which returns in a custom string object format.
Here custom toString() in the HelloObject will convert the Object into String representation format.
As per output, we can see the list of string.
Interview Question 2 -> ArrayList vs LinkedList:
Array List in java API applies a dynamic array to store the elements.
Whereas LinkedList uses a double linked list to store the elements.
Also, the ArrayList String value can convert to a byte array using the Java programming language.
Again both ArrayList and LinkedList accept duplicate values.
But we can remove duplicates using plain Java code, Lambdas, Guava.
Join Method (StringUtils)
We can use the join method of Apache Commons Lang StringUtils class to achieve the java list to string conversion.
StringUtils.join method have inbuilt toString() method.
As we can see from the above output, it prints the List elements as String data type with space delimiter.
we can also use java regular expressions to define a search pattern for strings.
A regular expression is best applicable for pattern matching of expressions or functions.
Here is the maven dependency for Apache commons-lang StringUtils class of java API.
you can use this in your project pom.xml file as a dependency.
The latest version of the dependency will be available here.
Stream Collectors
java list to string
Now let’s use the Java Util Stream Collectors API package to convert List to String.
Here we leverage Java streams method stream() for conversion.
In the above example, we can see the usage of the stream(). map, note that it is different from standard java map.
Comma Separator(delimiter)
Let’s go through how to convert using comma-separated values.
As per the output above, we can see conversion using delimiter i,e. separated by Comma or Comma separated.
Using join method, you can convert List to String with Separator comma, backslash, space, and so on.
Convert Character List to String
Let’s go through how to convert List of Characters to String using StringBuilder class.
with Double Quotes
Using Apache Commons StringUtils package, convert List to String with Quotes using Java.
Refer to the below implementation
Of course, you can convert using Single Quotes with Single String as well.
Sort Method
we can convert using Java Sort with the below implementation.
toJson Method
Let’s convert List to String JSON in Java using Google GSON library.
It is a straight forward method ToJson() which will set and convert the input to JSON String.
In Java 8
Let’s convert List to String using String.join() method in Java 8.
replaceAll Method
Lets convert List to String using replaceAll() and String.join() method.
You can also notice inline lambda expressions used in the replaceAll method.
LinkedList to String
Let’s convert LinkedList to String using String.join() method.
In case of any issues during conversion, we can notice the error message in the console log.
To conclude, in this tutorial we gone through different ways to convert a Java List to String data type.
List to String methods conversion is also common in other programming languages like JavaScript, Python, Jquery.
In a nutshell, JavaScript uses an str function for concatenate, likewise, the python program uses join method for conversion and concatenate a string.
Interested to read JavaScript resources, check out this JavaScript split method article.
Преобразование списка в строку Java
В этом посте мы обсудим, как преобразовать список в строку в Java. Решение должно объединять элементы предоставленного списка в одну строку с заданным разделителем. Решение не должно добавлять разделитель до или после списка.
1. Использование StringBuilder
Идея состоит в том, чтобы пройтись по списку и объединить каждый элемент списка с StringBuilder экземпляр с указанным разделителем. Наконец, мы возвращаем строковое представление StringBuilder . Обратите внимание, что решение должно иметь дело с завершающими символами разделителей.
Java Program to Convert the ArrayList into a string and vice versa
In this example, we will learn to convert the arraylist into a string and vice versa in Java.
To understand this example, you should have the knowledge of the following Java programming topics:
Example 1: Convert the Arraylist into a String
Output
In the above example, we have created an arraylist named languages . Notice the line,
Here, the toString() method converts arraylist into a string. The entire arraylist is converted as a single string.
Note: We can also convert the arraylist into a string array. To learn more, visit Java ArrayList to Array Conversion.
Example 2: Convert ArrayList to String Using join()
Output
In the above example, we have used the join() method of the String class to convert the arraylist into a string. To learn more, visit Java String join().
Example 3: Convert a String to ArrayList
Output
In the above example, we have created a string named str . We have used the split() method to convert the given string into an array. To learn more about splitting a string, visit Java String split().
Преобразование ArrayList в массив String[] в Java
Преобразование коллекций в массивы — это общая задача, с которой сталкиваются разработчики на Java. Например, есть задача преобразовать ArrayList<String> в массив String[].
Предположим, есть следующий ArrayList<String>:
Задача — преобразовать его в массив String[]. Первый подход, который может прийти в голову — это использовать метод toArray() :
Однако, этот код вызовет ClassCastException на этапе выполнения, так как метод toArray() возвращает массив Object[] , а не String[] .
Для преобразования ArrayList<String> в String[] правильным путем будет использование перегруженной версии метода toArray(T[] a) . Этот метод возвращает массив, содержащий все элементы списка в правильной последовательности; типом возвращаемого массива будет тип массива, переданного в метод. Если список вмещает в переданный массив, он возвращается. В противном случае, новый массив выделяется с типом и размером переданного массива.
Вот как правильно преобразовать ArrayList<String> в String[]:
В этом примере создается новый массив String[] с размером 0. Если список больше этого размера, то метод toArray() сам выделит память под новый массив нужного размера. Если же размер списка меньше или равен размеру переданного массива, то будет использован переданный массив. Значения списка будут помещены в этот массив и он будет возвращен.
Таким образом, для преобразования ArrayList<String> в String[] нужно использовать метод toArray(T[] a) , передав в него массив нужного типа.