Java - String indexOf() method example

Simple example:

String text = "Here we are";
int index = text.indexOf("H"); // 0

System.out.println( text.indexOf("H")   ); // 0
System.out.println( text.indexOf("e")   ); // 1
System.out.println( text.indexOf("r")   ); // 2
System.out.println( text.indexOf(" ")   ); // 4
System.out.println( text.indexOf("we")  ); // 5
System.out.println( text.indexOf("are") ); // 8

In this post we cover usage of String indexOf() method with simple code examples.

Definition:

We use Java String indexOf() method to find index of specified substring or char in given String.

1. String indexOf(String str)

public class Example1 {

    public static void main(String[] args) {

        String text = "Here we are";
        int index = text.indexOf("we");
        System.out.println(index); // 5
    }
}

Output:

5

Why indexOf() method printed index 5? Explanation below.

2. Explanation of index

Why indexOf() method printed index 5?

Below code prints indexes of each character.

public class IndexExplanation {

    public static void main(String[] args) {

        String text = "Here we are, we";
        for (int i = 0; i < text.length(); i++) {
            System.out.println("index: " + i + ", char: " + text.charAt(i));
        }
    }
}

Output:

index: 0, char: H
index: 1, char: e
index: 2, char: r
index: 3, char: e
index: 4, char:
index: 5, char: w
index: 6, char: e
index: 7, char:
index: 8, char: a
index: 9, char: r
index: 10, char: e
index: 11, char: ,
index: 12, char:
index: 13, char: w
index: 14, char: e

Another short explanation of index

// index:      0123456789..
String text = "Here we are";
// index of 'we' is 5

3. String indexOf(String str, int fromIndex)

public class Example3 {

    public static void main(String[] args) {

        String text = "Here we are, we";
        int index = text.indexOf("we", 6);
        System.out.println(index); // 13
    }
}

Output:

13

4. String indexOf(int ch)

public class Example4 {

    public static void main(String[] args) {

        String text = "Here we are";
        int index = text.indexOf('w');
        System.out.println(index); // 5
    }
}

Output:

5

5. String indexOf(int ch, int fromIndex)

public class Example5 {

    public static void main(String[] args) {

        String text = "Here we are, we";
        int index = text.indexOf('w', 6);
        System.out.println(index); // 13
    }
}

Output:

13

6. Versions of String indexOf method

Java provides 4 versions of indexOf with different parameters:

• public int indexOf(String str)

• public int indexOf(String str, int fromIndex)

• public int indexOf(int ch)

• public int indexOf(int ch, int fromIndex)

The most popular version of indexOf() method is

• public int indexOf(String str)

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