String equalsIgnoreCase() Java Example

In this post, we feature a comprehensive article about the equalsignorecase Java ‘s String Method.

1. Introduction

Java String class has provided the java equalsignorecase method to compare this String to another String by ignoring case since version 1. Here is the method’s signature:

boolean equalsIgnoreCase​(String anotherString)

The String class inherits the equals method from the Object class. It returns true if and only if the argument is not null and is a String object that represents the same sequence of characters as this object.

public boolean equals​(Object anObject)

In this example, I will demonstrate:

• Compare two strings with equals and equalsIgnoreCase methods
• Compare two strings with customized methods
• Show the difference when comparing String literal and String object
• Show the difference when comparing with the == operator and equals(), equalsIgnoreCase() methods

2. Technologies Used

The example code in this example was built and run with:

• Java 11
• Maven 3.3
• Eclipse
• Junit 4.12

3. Maven Project

3.1 Dependencies

I will include Junit in the pom.xml.

pom.xml

<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.jcg.zheng.demo</groupId>
	<artifactId>string-equals-unittest</artifactId>
	<version>0.0.1-SNAPSHOT</version>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
	</properties>

	<build>
		<sourceDirectory>src</sourceDirectory>
		<plugins>
			<plugin>
				<artifactId>maven-compiler-plugin</artifactId>
				<version>3.8.0</version>
				<configuration>
					<release>11</release>
				</configuration>
			</plugin>
		</plugins>
	</build>
	<dependencies>
		<dependency>
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
			<version>4.12</version>
		</dependency>
	</dependencies>
</project>

3.2 Customized equalsIgnoreCase

In this step, I will create a StringEqualsTest class which compares two strings with the equals method after converting them into upper case and lower case.

StringEqualsUtil.java

package org.jcg.zheng;

public class StringEqualsUtil {

	public boolean equalsIgnoreCase_via_uppercase(String data, String compareString) {
		if( data == null) {
			if ( compareString == null) {
				return true;
			}
			return false;
		} else {
			if ( compareString == null) {
				return false;
			}
			return data.toUpperCase().equals(compareString.toUpperCase());
		}

	}
	
	public boolean equalsIgnoreCase_via_lowercase(String data, String compareString) {
		if( data == null) {
			if ( compareString == null) {
				return true;
			}
			return false;
		} else {
			if ( compareString == null) {
				return false;
			}
			return data.toLowerCase().equals(compareString.toLowerCase());
		}

	}

}

4. JUnit Test

4.1 StringLiteralTest

In this step, I will create a Junit test class with three tests:

• The "==" operator compares two objects based on the object reference. Please see line 17 and 28.
• The equalsIgnorecase compares two String base on the value. Please see line 19 and 30.
• The equals compares this String object has same value with another object. Please see line 18 and 29.

StringLiteralTest.java

package org.jcg.zheng;

import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;

import org.junit.Test;

public class StringLiteralTest {
 @Test
 public void equalsOperator_and_equalsMthods_on_object_string() {
 // == operator compares two objects have the same object reference
 // equals and equals compare two object has the same content value

 String firstString = new String("Test");
 String secondString = new String("Test");

 assertFalse(firstString == secondString);
 assertTrue(firstString.equals(secondString)); 
 assertTrue(firstString.equalsIgnoreCase(secondString)); 
 }

 @Test
 public void equalsOperator_and_equalsMthods_on_object_literal_string() {
 // Java internally provides String pool for the literal String,
 String firstString = "Test";
 String secondString = "Test";

 assertTrue(firstString == secondString);
 assertTrue(firstString.equals(secondString));
 assertTrue(firstString.equalsIgnoreCase(secondString)); 
 }

 @Test
 public void test_null() {
 assertTrue(null == null);

 String testString = "Demo";
 assertFalse(testString.equals(null));

 assertFalse(testString.equalsIgnoreCase(null));

 }

}

Execute mvn clean test -Dtest=StringLiteralTest and capture the output here.

Output

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running org.jcg.zheng.StringLiteralTest
Tests run: 3, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.108 sec

Results :

Tests run: 3, Failures: 0, Errors: 0, Skipped: 0

4.2 StringEqualsTest

In this step, I will create a StringEqualsTest class which will test both equals and equalsIgnoreCase from the String class. It will also test the two customized equalsIgnoreCase built at step 3.2. It includes six tests and displays the results in the system console.

StringEqualsTest.java

package org.jcg.zheng;

import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;

import org.junit.Test;

public class StringEqualsTest {
	private StringEqualsUtil strUtil = new StringEqualsUtil();

	private void compareString(String compareMethod) {
		String testString = "ABC";
		char[] firstChar = { 'A', 'a' };
		char[] secondChar = { 'B', 'b' };
		char[] thirdChar = { 'C', 'c' };

		for (char first : firstChar) {
			for (char second : secondChar) {
				for (char third : thirdChar) {
					char[] matchChars = { first, second, third };

					String matchString = String.valueOf(matchChars);

					switch (compareMethod) {
					case "equalsIgnoreCase":
						assertTrue(testString.equalsIgnoreCase(matchString));
						System.out.printf("'%s' equalsIgnoreCase '%s', ret = %b\n", testString, matchString,
								testString.equalsIgnoreCase(matchString));

						break;
					case "test_equals_string":
						System.out.printf("'%s' equals '%s', ret = %b\n", testString, matchString,
								testString.equals(matchString));

						break;
					case "test_equals_charArray":
						System.out.printf("'%s' equals '%s', ret = %b\n", testString, matchChars,
								testString.equals(matchChars));
						break;
					case "equalsIgnoreCase_via_uppercase":
						assertTrue(strUtil.equalsIgnoreCase_via_uppercase(testString, matchString));
						System.out.printf("'%s' equalsIgnoreCase_via_uppercase '%s', ret = %b\n", testString,
								matchString, strUtil.equalsIgnoreCase_via_uppercase(testString, matchString));
						break;

					case "equalsIgnoreCase_via_lowercase":
						assertTrue(strUtil.equalsIgnoreCase_via_lowercase(testString, matchString));
						System.out.printf("'%s' equalsIgnoreCase_via_lowercase '%s', ret = %b\n", testString,
								matchString, strUtil.equalsIgnoreCase_via_lowercase(testString, matchString));
						break;
					}
				}
			}
		}
	}

	@Test
	public void test_equals_charArray() {
		compareString("test_equals_charArray");
	}

	@Test
	public void test_equals_string() {
		compareString("test_equals_string");
	}

	@Test
	public void test_equalsIgnoreCase() {
		compareString("equalsIgnoreCase");
	}

	@Test
	public void test_equalsIgnoreCase_via_lowercase() {
		compareString("equalsIgnoreCase_via_lowercase");
	}

	@Test
	public void test_equalsIgnoreCase_via_uppercase() {
		compareString("equalsIgnoreCase_via_uppercase");
	}

	@Test
	public void test_null() {
		assertTrue(strUtil.equalsIgnoreCase_via_uppercase(null, null));
		assertFalse(strUtil.equalsIgnoreCase_via_uppercase(null, "NA"));
		assertFalse(strUtil.equalsIgnoreCase_via_uppercase("NA", null));

		assertTrue(strUtil.equalsIgnoreCase_via_lowercase(null, null));
		assertFalse(strUtil.equalsIgnoreCase_via_lowercase(null, "NA"));
		assertFalse(strUtil.equalsIgnoreCase_via_lowercase("NA", null));
	}

}

Execute mvn clean test -Dtest=StringLiteralTest and capture the output here.

Output

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running org.jcg.zheng.StringEqualsTest
'ABC' equals 'ABC', ret = true
'ABC' equals 'ABc', ret = false
'ABC' equals 'AbC', ret = false
'ABC' equals 'Abc', ret = false
'ABC' equals 'aBC', ret = false
'ABC' equals 'aBc', ret = false
'ABC' equals 'abC', ret = false
'ABC' equals 'abc', ret = false
'ABC' equalsIgnoreCase 'ABC', ret = true
'ABC' equalsIgnoreCase 'ABc', ret = true
'ABC' equalsIgnoreCase 'AbC', ret = true
'ABC' equalsIgnoreCase 'Abc', ret = true
'ABC' equalsIgnoreCase 'aBC', ret = true
'ABC' equalsIgnoreCase 'aBc', ret = true
'ABC' equalsIgnoreCase 'abC', ret = true
'ABC' equalsIgnoreCase 'abc', ret = true
'ABC' equals '[C@a38d7a3', ret = false
'ABC' equals '[C@77f99a05', ret = false
'ABC' equals '[C@63440df3', ret = false
'ABC' equals '[C@3aeaafa6', ret = false
'ABC' equals '[C@76a3e297', ret = false
'ABC' equals '[C@4d3167f4', ret = false
'ABC' equals '[C@ed9d034', ret = false
'ABC' equals '[C@6121c9d6', ret = false
'ABC' equalsIgnoreCase_via_lowercase 'ABC', ret = true
'ABC' equalsIgnoreCase_via_lowercase 'ABc', ret = true
'ABC' equalsIgnoreCase_via_lowercase 'AbC', ret = true
'ABC' equalsIgnoreCase_via_lowercase 'Abc', ret = true
'ABC' equalsIgnoreCase_via_lowercase 'aBC', ret = true
'ABC' equalsIgnoreCase_via_lowercase 'aBc', ret = true
'ABC' equalsIgnoreCase_via_lowercase 'abC', ret = true
'ABC' equalsIgnoreCase_via_lowercase 'abc', ret = true
'ABC' equalsIgnoreCase_via_uppercase 'ABC', ret = true
'ABC' equalsIgnoreCase_via_uppercase 'ABc', ret = true
'ABC' equalsIgnoreCase_via_uppercase 'AbC', ret = true
'ABC' equalsIgnoreCase_via_uppercase 'Abc', ret = true
'ABC' equalsIgnoreCase_via_uppercase 'aBC', ret = true
'ABC' equalsIgnoreCase_via_uppercase 'aBc', ret = true
'ABC' equalsIgnoreCase_via_uppercase 'abC', ret = true
'ABC' equalsIgnoreCase_via_uppercase 'abc', ret = true
Tests run: 6, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.214 sec

Results :

Tests run: 6, Failures: 0, Errors: 0, Skipped: 0

Note: As you see at results here, equalsIgnoreCase comparing string value without considering the case.

5. Summary

In this example, I demonstrated how to use the String equalsIgnoreCase method and compare it to equals. I also demonstrated the difference when comparing with "==” operator and String literal.

6. Download the Source Code

This was an example on Java String.equalsIgnoreCase() Method .This example consists of a Maven project which defines seven test classes to demonstrate the equalsIgnoreCase method’s usages.

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