Char array, String

Often we need Strings to pass to methods and use in Java programs. But sometimes, we have character data in an array—a char array—and must convert it.

With the String constructor, we can convert a char array to a String. We can convert even just a range of characters in the char array. One or three arguments are needed.

Char array to String

This program uses the String constructor. It first creates and fills a char array of 8 characters. It then converts char ranges to Strings.

public class Program {
    public static void main(String[] args) {

        // An example char array.
        char[] values = new char[8];
        values[0] = 'W';
        values[1] = 'e';
        values[2] = 'l';
        values[3] = 'c';
        values[4] = 'o';
        values[5] = 'm';
        values[6] = 'e';
        values[7] = '!';

        // Create a string with the entire char array.
        String result = new String(values);
        System.out.println(result);

        // Use first 7 characters for a new String.
        String result2 = new String(values, 0, 7);
        System.out.println(result2);

        // Create a string with an offset.
        String result3 = new String(values, 3, 4);
        System.out.println(result3);
    }
}
Welcome!
Welcome
come

ToCharArray

The String class provides a useful toCharArray method. This takes the characters in the string and places them in a new char array.

public class Program {
    public static void main(String[] args) {

        // A string.
        String value = "HERO";
        System.out.println(value);

        // Convert String to char array with toCharArray method.
        char[] result = value.toCharArray();
        for(char element:result)
        {
            System.out.println(element);
        }

        // Round-trip our conversion.
        String roundTrip = new String(result);
        System.out.println(roundTrip);
    }
}
HERO
H
E
R
O
HERO

For performance, I have found that avoiding String creation is a good option. If you can redesign your methods to use char arrays, you can often avoid many allocations.

Chars are two bytes

In a char array, we can manipulate these elements without forcing a String allocation. This improves performance.

With char arrays, we introduce extra complexity to our algorithms. But the benefits outweigh the costs. With the String constructor and toCharArray we convert back to Strings.