length and charAt
- Java course
- Beginner
- Lesson 30/116
- 4 min
Learn string access with length() and charAt().
length and charAt
The length of a String is given by the length() method. To get a specific character use charAt(i); i starts at zero.
String name = "Alex";
int n = name.length(); // 4
char first = name.charAt(0); // 'A'The first character has index 0, the last has index length() - 1. Going beyond this throws StringIndexOutOfBoundsException.
In loops, i < name.length() is a safe bound.
Index bounds
String indices start at 0. For a String of length n, valid indices are between 0 and n - 1.
String s = "Java"; // length 4
s.charAt(0); // 'J' - valid
s.charAt(3); // 'a' - valid (last)
s.charAt(4); // ERROR!An out-of-range index throws StringIndexOutOfBoundsException. So loops use i < s.length(), not i <= s.length().
Practice Use length and charAt
Write a Main class with a main method. Assign "Java" to String word. Print word.length() and word.charAt(0) on separate lines with println.
Sample solution
public class Main {
public static void main(String[] args) {
String word = "Java";
System.out.println(word.length());
System.out.println(word.charAt(0));
}
}Expected output
4 J
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does "Java".length() return?
- 4 Correct answer
- 3
- 5
- 0
Explanation: length() gives the character count.
2 Complete the charAt call
char first = name.____(0);char first = name.charAt(0);Explanation: charAt(0) gives the first character.
3 Match the methods
| Term | Meaning |
|---|---|
length() |
Length |
charAt(0) |
First char |
charAt(n-1) |
Last char |
"Java" |
String |