How to Use Java String Class indexOf() Method

Function Description

Java String class indexOf() method is used to get the index value of the first occurrence of the specified character or the sequence of characters within the string. Search starts from the specified index, if fromIndex is given. If fromIndex value is not given, the search starts from 0 index.

It returns -1, if it does not find the specified character or sequence of characters within the String.

If the fromIndex value is negative(-ve), it will have the same effect as index value 0 and the entire string will be searched.

If the fromIndex value is greater than the length of the string, it will have the same effect as the length of the string and will return -1.

In java indexOf() method is defined as overloaded method

1. Method to get the index value of the first occurrence of the specified character within the string.
   
   
2. Method to get the index value of the first occurrence of the specified character within the string. The specified character search starts from the specified index.
   
   
3. Method to get the index value of the first occurrence of the specified string within the string.
   
   
4. Method to get the index value of the first occurrence of the specified sequence of characters(string) within the string. The specified string search starts from the specified index.

Method Signature

Method to get the index value of the first occurrence of the specified character within the string. In this method, the search starts from 0 index.

public int indexOf(int ch)

Method to get the index value of the first occurrence of the specified character within the string. Specified character search starts from the specified fromIndex. 

public int indexOf(int ch, int fromIndex)

Method to get the index value of the first occurrence of the specified string within the string

public int indexOf(String str)

Method to get the index value of the first occurrence of the specified sequence of characters(string) within the string. The specified string search starts from the specified index.

public int indexOf(String str, int fromIndex)

Parameter(s)

ch : Character for which first occurrence of index value to be searched.

fromIndex: Starting index value from where character/sequence of characters will be searched.

str: Sequence of characters(string) for which the first occurrence of index value to be searched.

Return

Index value of the first occurrence of character/sequence of characters within the string/substring in int datatype. It returns -1, if specified character/sequence of characters does not find within the string

Examples of Java String Class indexOf() Method

Example to get the index value of the first occurrence of the specified character within the string

public class ExampleStringIndexOf {
 
    private void getIndexOfCharacter() {

          String str = new String("Welcome to String class indexOf() function learning");

          // returns the index value S character

          int indexValue = str.indexOf('S');

          System.out.println("Index value of S character : " + indexValue);
 
          // returns the index value f character

          indexValue = str.indexOf('f');

          System.out.println("Index value of f character : " + indexValue);
    }
 
   
    public static void main(String[] args) {

          ExampleStringIndexOf example = new ExampleStringIndexOf();

          example.getIndexOfCharacter();
    }
 
}


Output:

Index value of S character : 11

Index value of f character : 30

Example to get the index value of the first occurrence of the specified character within the string for which fromIndex value is given to start the search at.

public class ExampleStringIndexOf {
 
    private void getIndexOfCharacterFromSpecifiedIndex() {

          String str = new String("Welcome to String class indexOf() function learning");

          int indexOfS = str.indexOf('S',10);

          System.out.println("Index value of S character while search starts from index value 10 is " + indexOfS);
 
          indexOfS = str.indexOf('W', 5);

          System.out.println("Index value of W character while search starts from index value 5 is" + indexOfS);

    }
 
    public static void main(String[] args) {

          ExampleStringIndexOf example = new ExampleStringIndexOf();

          example.getIndexOfCharacterFromSpecifiedIndex();
    }
 
}

Output:

Index value of S character while search starts from index value 10 is 11

Index value of W character while search starts from index value 5 is-1

Example to get the index value of the first occurrence of the specified string within the String

public class ExampleStringIndexOf {
 
    private void getIndexOfString() {

          String str = new String("Welcome to String indexOf function learning");

          // returns index value of 'function' string

          int indexValue = str.indexOf("function");

          System.out.println("Index value of 'function' = " + indexValue);
         
          System.out.println("Index value of 'Welcome' = " + str.indexOf("Welcome"));
         
          System.out.println("Index value of 'test' = " + str.indexOf("test"));

    }
  
   
    public static void main(String[] args) {
 
         ExampleStringIndexOf example = new ExampleStringIndexOf();

          example.getIndexOfString();
    }
 
}

Output:

Index value of 'function' = 26

Index value of 'Welcome' = 0

Index value of 'test' = -1

Example to get the index value of the first occurrence of the specified sequence of characters(string) within the string while fromIndex value is given to start the search at.

public class ExampleStringIndexOf {
 
    private void getIndexOfStringFromSpecifiedIndex() {

          String str = new String("Welcome to String indexOf function learning");

          // returns index value of 'function', searching from index value 5

          int index = str.indexOf("function", 5);

          System.out.println("Index value of 'function', searching from index value 5 is" + index);
 
          // returns index value of 'Welcome',searching from index value 5

          index = str.indexOf("Welcome", 5);

          System.out.println("Index value of 'Welcome', searching from index value 5 is " + index);
 
    }
 
    public static void main(String[] args) {

          ExampleStringIndexOf example = new ExampleStringIndexOf();

          example.getIndexOfStringFromSpecifiedIndex();
    }
 
}
 

Output:

Index value of 'function', searching from index value 5 is 26

Index value of 'Welcome', searching from index value 5 is -1

Other Methods of String Class

In this article, we learned all about the indexOf() method of Java String class with examples. Apart from the IndexOf() method, we got an idea about other String methods too. We will come up with more articles explaining other String methods with examples. For more details please click on the respective methods link.