Chryssa Aliferi

About Chryssa Aliferi

Chryssa is a Computer Science graduate from Athens University of Economic and Business. During her studies, Chryssa carried out a great variety of projects ranging from networking to software engineering. She is very keen on front end development especially on mobile technologies and web applications.

Java String indexOf Example

It is often important to search for a character or a character set in a Java String. For example, in the parsing of Java Strings, we might want to provide the possibility for a search through strings, in order to find a specific character or word. Thus we need a “tool”, a method that will help us make it.

So, in this example we are going to talk about identifying characters and subsequences of characters through Java Strings, with the method indexOf().

String static indexOf() method:

The indexOf()(String or character target) method searches left-to-right inside the given string for a “target” string. The method returns the index number where the target string is first found or -1 if the target is not found. Like equals(), the indexOf() method is case-sensitive, so uppercase and lowercase chars are considered to be different.

  • int indexOf(String str): Returns the index within this string of the first occurrence of the specified substring. If it does not occur as a substring, -1 is returned.
  • int indexOf(String str, int fromIndex): Returns the index within this string of the first occurrence of the specified substring, starting at the specified index. If it does not occur, -1 is returned.

We can use the same methods in order to find the index of the first occurrence of a specified character within the string:

  • int indexOf(int ch)
  • int indexOf(int ch, int fromIndex)

Example:

JavaStringIndexOf.java

package com.javacodegeeks.javabasics.string;

public class JavaStringIndexOf {

   public static void main(String args[]) {

   String str = new String("Hello JavaCodeGeeks! This is my very first post.");

   String subStr1 = new String("JavaCodeGeeks");
   String subStr2 = new String("JavaGeeks");

   System.out.print("Found Index :");
   System.out.println(str.indexOf('e')); //finds the first occurence of 'e'

   System.out.print("Found Index :");
   System.out.println(str.indexOf('e', 5)); //finds the occurence of 'e' after the 5th character

   System.out.print("Found Index :");
   System.out.println(str.indexOf(subStr1)); //finds the first occurence of "JavaCodeGeeks"

   System.out.print("Found Index :");
   System.out.println(str.indexOf(subStr1, 15)); //finds the occurence of "JavaCodeGeeks" after the 15th character

   System.out.print("Found Index :");
   System.out.println(str.indexOf(subStr2)); //finds the first occurence of "JavaGeeks"

   }
}

Output:


Found Index :1
Found Index :13
Found Index :6
Found Index :-1
Found Index :-1

This was the example of Java String indexOf() method.

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