How do I get char value of a string at a specified position?

The chartAt() method of the String class returns the char value at the specified index. An index ranges from 0 to length() - 1. If we specified an index beyond of this range a StringIndexOutOfBoundsException exception will be thrown.

These method use zero based index which means the first char value of the sequence is at index 0, the next at index 1, and so on, as for array indexing.

package org.kodejava.example.lang;

public class CharAtExample {
    public static void main(String[] args) {
        String[] colors = {"black", "white", "brown", "green", "yellow", "blue"};

        for (String color : colors) {
            // Get char value of a string at index number 3. Because
            // the index is zero based we'll get the fourth character
            // of each color in the array.
            char value = color.charAt(3);
            System.out.printf("The fourth char of %s is '%s'.%n", color, value);
        }

    }
}

Here is the program output:

The fourth char of black is 'c'
The fourth char of white is 't'
The fourth char of brown is 'w'
The fourth char of green is 'e'
The fourth char of yellow is 'l'
The fourth char of blue is 'e'

How do I replace characters in string?

package org.kodejava.example.lang;

public class StringReplace {
    public static void main(String[] args) {
        String text = "The quick brown fox jumps over the lazy dog";
        System.out.println("Before: " + text);

        // The replace method replace all occurrences of character
        // 'o' with 'u' and returns a new string object.
        text = text.replace('o', 'u');
        System.out.println("After : " + text);
    }
}

The result of the code snippet:

Before: The quick brown fox jumps over the lazy dog
After : The quick bruwn fux jumps uver the lazy dug

How do I create a repeated sequence of character?

This example show you how to create a repeated sequence of characters. To do this we use the Arrays.fill() method. This method fills an array of char with a character.

package org.kodejava.example.util;

import java.util.Arrays;

public class RepeatCharacterExample {
    public static void main(String[] args) {
        char c = 'x';
        int length = 10;

        // creates char array with 10 elements
        char[] chars = new char[length];

        // fill each element of chars array with 'x'
        Arrays.fill(chars, c);

        // print out the repeated 'x'
        System.out.println(String.valueOf(chars));
    }
}

As the result you get the x character repeated 10 times.

xxxxxxxxxx

For one liner code you can use the following code snippet, which will give you the same result.

new String(new char[10]).replace('\0', 'x');

Or

String.join("", Collections.nCopies(10, "x"));