Extract Characters From Strings

You can extract characters from strings in a number of ways. We discuss about each technique in this section.

Internally, strings store characters in an array. However, you cannot access the characters of the string using the array subscript operator. But many methods in the String class require indexes to operate. Just like array, string indexes are zero based. So it would help you to understand strings better if you think of them as arrays.

You can extract a single character from a String using the charAt() method. It accepts an index of the character you want to retrieve. You cannot specify negative values. It throws a StringIndexOutOfBoundsException if the index is invalid.

Here is the declaration of the chartAt() method.

char charAt(int where)

It returns the character at the specified index.

Here is an example.

String color = "Neon";
char c = color.charAt(2);
System.out.println(c);

This snipet prints the following output.

o

You can retrieve a range of characters at a time using the getChars() method.

Here is the declaration of the getChars() method.

void getChars(int startIndex, int stopIndex, char[] destination, int destinationIndex)

Here, the startIndex specifies the index from which the copying begins. It is inclusive.

The stopIndex specifies the index at which the copying ends. This index is exclusive, which means the character at this index is not copied.

The characters are copied to the destination array you specify. The characters are copied into the destination array beginning at the index specified by destinationIndex. You need to make sure that the destination array is large enough to store the range of characters.

Here is an example which copies a range of characters.

public class ExtractRangeOfCharactersDemo {

    public static void main(String ... arguments) {
        String message = "How you doin?";
        int startIndex = 4;
        int stopIndex = 7;
        char[] destination = new char[3];
        message.getChars(startIndex, stopIndex, destination, 0);
        
        String message2 = new String(destination);
        System.out.println(message2);
    }
}

This example prints the following.

you

If you want to convert all the characters in your string into a character array, invoke the toCharArray() method. It returns an array of characters from your string.

The declaration of the toCharArray() method is shown here.

char[] toCharArray()

You can use the getChars() method to perform the same operation, except getChars() makes you write more code.

The substring() method allows you to extract a region of your string, usually referred as substring.

The declaration of this method is shown here.

String substring(int index)

Here, the index indicates the index from which the substring is extracted. The substring begins from the specified index and extends to the end of the string.

Here is an example of the substring() method.

String lastName = "Nikola Tesla".substring(7);
System.out.println(lastName);

This example prints the following output.

Tesla

An overloaded version of the substring() method allows you to extract a range of characters from the string.

Here is the declaration of the substring() method.

String substring(int startIndex, int stopIndex)

Here the startIndex specifies the start index of the substring and the stopIndex specifies the end index of the substring. The startIndex is inclusive, whereas, the stopIndex is exclusive.

Here is an example of the overloaded version of the substring() method.

String name = "Nikola Tesla".substring(2, 6);
System.out.println(name);

This example prints the following output.

kola