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How to initialize an array in one line in Java

How to initialize an array in one line in Java

Gareth D.

—

The Problem

In Java, you can declare an array and then add items to specific elements as follows:

Click to Copy
public class Main {

    public static void main(String[] args) {
        String[] words = new String[4];
        words[0] = "java";
        words[1] = "arrays";
        words[2] = "are";
        words[3] = "easy";
        System.out.println(words[0]);
        System.out.println(words[1]);
    }
}

However, sometimes you have all the data you need when you initialize the array, and you want to initialize the array using less code.

How can you initialize an array in one line in Java?

The Solution

You can specify the initial values for each item in an array using braces{...}. The code sample below is equivalent to the previous one.

Click to Copy
public class Main {

    public static void main(String[] args) {
        String[] words = {"java", "arrays", "are", "easy"};
        System.out.println(words[0]);
        System.out.println(words[1]);
    }
}

Output:

Click to Copy
java
arrays

Note that with this syntax, you do not specify the array length, as you usually do when creating an array in Java. The compiler will count the elements and create an array of the correct size for you.

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// this will throw an error
String[4] words = {"java", "arrays", "are", "easy"};

If you want to use an ArrayList collection instead of an array, you cannot use the {...} initialization syntax. Instead, you can achieve the same in one line using Arrays.asList, as in the following example:

Click to Copy
import java.util.ArrayList;
import java.util.Arrays;

public class Main {

    public static void main(String[] args) {
        ArrayList<String> words = new ArrayList<>(Arrays.asList("java", "arrays", "are", "easy"));
        System.out.println(words.get(0));
        System.out.println(words.get(1));
    }
}

Output:

Click to Copy
java
arrays
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