Java String indexOf()

The Java String class indexOf() method returns the position of the first occurrence of the specified character or string in a specified string.

Signature

There are four overloaded indexOf() method in Java. The signature of indexOf() methods are given below:

No.	Method	Description
1	int indexOf(int ch)	It returns the index position for the given char value
2	int indexOf(int ch, int fromIndex)	It returns the index position for the given char value and from index
3	int indexOf(String substring)	It returns the index position for the given substring
4	int indexOf(String substring, int fromIndex)	It returns the index position for the given substring and from index

Parameters

ch: It is a character value, e.g. 'a'

fromIndex: The index position from where the index of the char value or substring is returned.

substring: A substring to be searched in this string.

Returns

Index of the searched string or character.

Internal Implementation

public int indexOf(int ch) {
        return indexOf(ch, 0);
    }

Java String indexOf() Method Example

FileName: IndexOfExample.java

public class IndexOfExample{
public static void main(String args[]){
String s1="this is index of example";
//passing substring
int index1=s1.indexOf("is");//returns the index of is substring
int index2=s1.indexOf("index");//returns the index of index substring
System.out.println(index1+"  "+index2);//2 8

//passing substring with from index
int index3=s1.indexOf("is",4);//returns the index of is substring after 4th index
System.out.println(index3);//5 i.e. the index of another is

//passing char value
int index4=s1.indexOf('s');//returns the index of s char value
System.out.println(index4);//3
}}

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Output:

2  8
5
3

We observe that when a searched string or character is found, the method returns a non-negative value. If the string or character is not found, -1 is returned. We can use this property to find the total count of a character present in the given string. Observe the following example.

FileName: IndexOfExample5.java

public class IndexOfExample5
{  
// main method
public static void main(String argvs[]) 
{   

String str = "Welcome to JavaTpoint";    
int count = 0;
int startFrom = 0;
for(; ;)
{

int index = str.indexOf('o', startFrom);

if(index >= 0)
{
// match found. Hence, increment the count
count = count + 1;

// start looking after the searched index
startFrom = index + 1;
}

else
{
// the value of index is - 1 here. Therefore, terminate the loop
break;
}

}

System.out.println("In the String: "+ str); 
System.out.println("The 'o' character has come "+ count + " times");
}  
}  

Output:

In the String: Welcome to JavaTpoint
The 'o' character has come 3 times

Java String indexOf(String substring) Method Example

The method takes substring as an argument and returns the index of the first character of the substring.

FileName: IndexOfExample2.java

public class IndexOfExample2 {
	public static void main(String[] args) {
		String s1 = "This is indexOf method";  		
		// Passing Substring  
		int index = s1.indexOf("method"); //Returns the index of this substring
		System.out.println("index of substring "+index);		
	}

}

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Output:

index of substring 16

Java String indexOf(String substring, int fromIndex) Method Example

The method takes substring and index as arguments and returns the index of the first character that occurs after the given fromIndex.

FileName: IndexOfExample3.java

public class IndexOfExample3 {
	public static void main(String[] args) {	
		String s1 = "This is indexOf method";  		
		// Passing substring and index
		int index = s1.indexOf("method", 10); //Returns the index of this substring
		System.out.println("index of substring "+index);
		index = s1.indexOf("method", 20); // It returns -1 if substring does not found
		System.out.println("index of substring "+index);		
	}
}

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Output:

index of substring 16
index of substring -1

Java String indexOf(int char, int fromIndex) Method Example

The method takes char and index as arguments and returns the index of the first character that occurs after the given fromIndex.

FileName: IndexOfExample4.java

public class IndexOfExample4 {
	public static void main(String[] args) {		
		String s1 = "This is indexOf method";  		
		// Passing char and index from
		int index = s1.indexOf('e', 12); //Returns the index of this char
		System.out.println("index of char "+index);		
	}
}

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Output: