How to convert to and from a String object in Java

String to/from array

Below are some examples of different ways to convert between arrays and their String representations.

In the examples we’ll make use of a Person class that you can check in the GitHub repository, but you can use the same approach with different types. Assume that our input array is:

private final Person[] peopleArray = new Person[] {
        new Person("Miss", "Jane", "Doe"),
        new Person("Mr", "John", "Doe"),
        new Person("Mr", "Name", "Surname")
};

Converting an array to a String using Stream

String resultString = Stream.of(peopleArray)
        .map(Person::toString) // 1
        .collect(Collectors.joining(", ")); // 2
System.out.println(resultString);

Output:

Miss. Jane Doe, Mr. John Doe, Mr. Name Surname

In this example, we have:

  1. A map operation that transforms the Person object into a String object using the toString method of the Person class, and finally,

  2. A Collector provided directly by Java that helps joining elements in the Stream using a given delimiter.

If you aren’t familiar with the :: notation, this is used to indicate a method reference. In this case, we are asking the Stream to map each Person object using the toString method. We could express the same end result in different ways, for example:

String resultString = Stream.of(peopleArray)
        .map(person -> {
            return person.toString();
        })
        .collect(Collectors.joining(", "));
System.out.println(resultString);

This would yield the same output as before.

There are different variations of the Collectors.joining method that allow for a prefix and suffix as well.

Converting an array to a String using a for-each loop

StringBuilder stringBuilder = new StringBuilder();
for (Person p : peopleArray) {
    stringBuilder.append(p.toString() + "\n");
}
System.out.println(stringBuilder.toString());

Output:

Miss. Jane Doe
Mr. John Doe
Mr. Name Surname

One thing to note is that if we want to achieve the same format as with the Collectors option we saw before, we need to add some additional checks to avoid including the comma separator after the last element.

We could do this using the following approach:

boolean firstElement = true;
StringBuilder stringBuilder = new StringBuilder();
for (Person p : peopleArray) {
    if (firstElement) {
        firstElement = false;
    } else {
        stringBuilder.append(", ");
    }
    stringBuilder.append(p.toString());
}
System.out.println(stringBuilder.toString());

Output:

Miss. Jane Doe, Mr. John Doe, Mr. Name Surname

Converting an array to a String using the Arrays class

String resultString = Arrays.toString(peopleArray);
System.out.println(resultString);

Output:

[Miss. Jane Doe, Mr. John Doe, Mr. Name Surname]

This option is the simplest one, but one that also provides less flexibility as you can’t alter the output format in the same way that the other options allow.

Converting a String into an array of Strings

In this example we’ll be covering String splitting. The conversion of a String into arrays of different types of objects will be covered in a later tutorial about marshalling/unmarshalling of data.

String inputString = "this,is,an,input,string";
String[] resultArray = inputString.split(",");

for (int i = 0; i < resultArray.length; i++) {
    System.out.println(String.format("%d: %s", i, resultArray[i]));
}

Output:

0: this
1: is
2: an
3: input
4: string

In this case, we are making use of the String.split method, indicating the comma as the delimiter. Note that the delimiter can be a regular expression.

The String.split method has an overloaded version that allows specifying the maximum number of elements that should be returned.

Code in GitHub

Get the code for this tutorial using the links below.

Project Repo
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Main class for this step