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What is StringUtils.indexOf in Java?

abhilash

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Overview

indexOf() is a staticthe methods in Java that can be called without creating an object of the class. method of the StringUtils used to find the index of the first occurrence of the search sequence in the given text. The matching of the search sequence in the given text is case-sensitive.

The method returns the -1 value for the following use cases:

  • If either of the given text or the search sequence is null.
  • If the search sequence is not present in the text.

The method returns the 0 value for the following use cases:

  • If the search sequence is an empty string.

The method returns a positive value for the following use cases:

  • If the search sequence is present in the given text.

The method optionally takes a parameter called startPos that indicates the starting index for matching of search sequence. A negative startPos is considered as zero.

Refer What is StringUtils.indexOfIgnoreCase in Java? for case-insensitive matching.

How to import StringUtils

The definition of StringUtils can be found in the Apache Commons Lang package, which we can add to the Maven project by adding the following dependency to the pom.xml file:


<dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
            <version>3.12.0</version>
</dependency>

For other versions of the commons-lang package, refer to the Maven Repository.

You can import the StringUtils class as follows:


import org.apache.commons.lang3.StringUtils;

Syntax


public static int indexOf(final CharSequence seq, final CharSequence searchSeq)
public static int indexOf(final CharSequence seq, final CharSequence searchSeq, final int startPos)

Parameters

  • seq: The text to search in.
  • searchSeq: The sequence to search.
  • startPos: The starting index of the search operation.

Return value

This method returns an integer value.

Code

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>test</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>

    <dependencies>

        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
            <version>3.12.0</version>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>2.1</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <transformers>
                                <transformer
                                        implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                    <mainClass>Main</mainClass>
                                </transformer>
                            </transformers>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

</project>

Explanation

The maven dependency for StringUtils is included in the pom.xml file:

Main.java

  • Line 1: We import the StringUtils class.
  • Lines 5-8: We define a search method that searches for the searchString in the given text by invoking the indexOf method.
  • Lines 10-13: We define a searchWithPos method that searches for the searchString in the given text with the starting index as startPos by invoking the indexOf method.
  • Lines 16-22: We invoke the search method for different text values and searchString.
  • Lines 24-32: We invoke the searchWithPos method for different text values, searchString and startPos.

Two observations to be made in the output:

  • The comparison is case-sensitive.
  • Only the index of the first occurrence of the searchString is returned.

RELATED TAGS

java
communitycreator

Grokking Modern System Design Interview for Engineers & Managers

Ace your System Design Interview and take your career to the next level. Learn to handle the design of applications like Netflix, Quora, Facebook, Uber, and many more in a 45-min interview. Learn the RESHADED framework for architecting web-scale applications by determining requirements, constraints, and assumptions before diving into a step-by-step design process.

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