String.toCharArray() / String.copyValueOf()

// Converts a string to a char array.
string.toCharArray();

// Creates a string from a char array.
String.copyValueOf(char[] data);
String.copyValueOf(char[] data, int offset, int count);

// Returns an IntStream of code points for each character in the string (Java 8 and later).
string.chars();

// Convert a string to a char array using toCharArray().
String str = "Hello";
char[] chars = str.toCharArray();
for (char c : chars) {
    System.out.print(c + " "); // Prints "H e l l o ".
}
System.out.println();

// Modify the char array, then convert it back to a string.
char[] arr = "banana".toCharArray();
arr[0] = 'B'; // Change the first character to uppercase.
String modified = new String(arr);
System.out.println(modified); // Prints "Banana".

// Create a string from a char array using String.copyValueOf().
char[] data = {'J', 'a', 'v', 'a'};
String result = String.copyValueOf(data);
System.out.println(result); // Prints "Java".

// Specify offset and count to extract a portion of the array.
String partial = String.copyValueOf(data, 0, 2);
System.out.println(partial); // Prints "Ja".

// Use chars() with the Stream API.
long count = "Hello World".chars()
        .filter(c -> c == 'l')
        .count();
System.out.println(count); // Prints "3".

toCharArray() converts a string into an array of char values. The returned array is a copy, so modifying its elements does not affect the original string (strings in Java are immutable). This is convenient when writing a loop to process a string one character at a time.

In Java 8 and later, chars() enables a more declarative style using the Stream API. Note that chars() returns a stream of int values (IntStream), not char values, so you must explicitly cast to (char) when treating the elements as characters.

To get the length of a string or retrieve a character at a specific position, use length() / charAt(). To extract a substring, use substring().