indexOf and substring

Learn searching and slicing with indexOf() and substring().

indexOf and substring

indexOf gives the first position of a substring. If not found, it returns -1. substring takes a slice.

String s = "Hello world";
int i = s.indexOf("wor");      // 6
String part = s.substring(0, 5); // "Hello"

substring(start) goes from start to the end; substring(start, end) goes from start to end (exclusive).

Check with if (i != -1) before using the found position.

Searching with indexOf

indexOf gives the first index where a character or substring appears. If not found, it returns -1.

String s = "Java";
int i = s.indexOf('a');  // 1 (first 'a')
int j = s.indexOf('z'); // -1 (not present)

If the result is -1, the substring is not present. So if (s.indexOf(x) != -1) is a common pattern.

To find the second occurrence, use the indexOf(x, start) form.

Exercise Use indexOf and substring

Write a Main class with a main method. Assign "Hello world" to String s. Print s.indexOf("world") and s.substring(0, 5) with println.

Show example solution

public class Main {
    public static void main(String[] args) {
        String s = "Hello world";
        System.out.println(s.indexOf("world"));
        System.out.println(s.substring(0, 5));
    }
}

Test yourself

Complete the substring call

String part = s.____(0, 5);

Show answer

String part = s.substring(0, 5);

Match the methods

indexOf

Search
substring

Slice
length

Length
charAt

Character
What does indexOf return when not found?
- 0
- null
- -1
- false
Show answer

-1 — indexOf returns -1 when not found.

Next lesson: toUpperCase and trim

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies