length and charAt

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().

Exercise 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.

Show example solution

public class Main {
    public static void main(String[] args) {
        String word = "Java";
        System.out.println(word.length());
        System.out.println(word.charAt(0));
    }
}

Test yourself

What does "Java".length() return?
- 4
- 3
- 5
- 0
Show answer

4 — length() gives the character count.

Complete the charAt call

char first = name.____(0);

Show answer

char first = name.charAt(0);

Match the methods

length()

Length
charAt(0)

First char
charAt(n-1)

Last char
"Java"

String

Next lesson: equals and equalsIgnoreCase

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