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

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 TutorAspire “;      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 TutorAspire 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);  }    }  

Test it Now

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);  }  }  

Test it Now

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);  }  }  

Test it Now

Output:

index of char 17

Next TopicJava String intern

example indexOf()java method signature string

Java String indexOf() method

Java String indexOf()

Signature

Parameters

Returns

Java String indexOf() Method Example

Java String indexOf(String substring) Method Example

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

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

Java ObjectInputStream

Java String toCharArray() method

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