In this article, we explain how to convert a String to Char Array in Java 8 through examples.
1. Introduction
The Java String class represents character strings. An array is a data structure which holds a fixed number of values of a single type. The char type is a primitive type which represents a single 16-bit Unicode character. It has a minimum value of '\u0000' (or 0) and a maximum value of '\uffff' (or 65535 inclusive). The Character class wraps thechar type as a value in an object. An object of theCharacter type contains a single field whose type is the chartype. A Char Array is an array which holds a constant number of characters.
Java 8 provides IntStream class which is useful to convert a String to an array of characters. In this example, I will demonstrate how to convert a String object into an array of characters.
2. Technologies used
The example code in this article was built and run using:
- Java 1.8.101
- Maven 3.3.9
- Eclipse Oxygen
- JUnit 4.12
3. Maven Project
3.1 Dependency
Add Junit to 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>zheng.jcg.demo</groupId> <artifactId>java8-demo</artifactId> <version>0.0.1-SNAPSHOT</version> <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> <scope>test</scope> </dependency> </dependencies> <build> <plugins> <plugin> <artifactId>maven-compiler-plugin</artifactId> <version>3.3</version> <configuration> <source>1.8</source> <target>1.8</target> </configuration> </plugin> </plugins> </build> </project>
3.2 Convert String to Char Array
JDK String class provides two methods:
charAt(int index)– return thecharvalue at the specified index.toCharArray()– return a newly allocated character array whose length is the length of this string and whose contents are initialized to contain the character sequence represented by this string.
In this step, I will show you how to use the methods above to convert a String into an array of characters.
StringToCharArray.java
package com.zheng.demo;
public class StringToCharArray {
private String testMessage;
public StringToCharArray(String message) {
super();
testMessage = message;
}
public char[] toCharArray() {
return testMessage.toCharArray();
}
public char[] toCharsBycharat2() {
char[] chars = new char[testMessage.length()];
for (int i = 0; i < testMessage.length(); i++) {
chars[i] = testMessage.charAt(i);
}
return chars;
}
public Character[] toCharsBycharat() {
Character[] chars = new Character[testMessage.length()];
for (int i = 0; i < testMessage.length(); i++) {
chars[i] = testMessage.charAt(i);
}
return chars;
}
}
3.3 Convert String to Char Array with Java 8
Java 8 IntStream interface is a sequence of int-valued elements. Java CharSequence interface provides the toChars method to return a stream of int values from the char sequence. Java String class implements the CharSequence interface and implements toChars .
In this step, I will show you how to convert a String object into an array of characters via IntStream.
StringToCharArray_Java8.java
package com.zheng.demo;
import java.util.stream.IntStream;
import java.util.stream.Stream;
public class StringToCharArray_Java8 {
private String testMessage;
public StringToCharArray_Java8(String message) {
super();
testMessage = message;
}
public Character[] toCharsByStream() {
IntStream is = testMessage.chars();
Stream characterStream = is.mapToObj(c -> (char) c);
return characterStream.toArray(Character[]::new);
}
public Character[] toCharsBycodePointsStream() {
IntStream is = testMessage.codePoints();
Stream characterStream = is.mapToObj(c -> (char) c);
return characterStream.toArray(Character[]::new);
}
}
4. JUnit Tests
4.1 Convert String to Char Array Test
In this step, I will create three JUnit tests to convert a String into an array of characters.
StringToCharArrayTest.java
package com.zheng.demo;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertTrue;
import org.junit.Test;
public class StringToCharArrayTest {
private StringToCharArray sv = new StringToCharArray("Test");
@Test
public void via_toCharArray() {
char[] chars = sv.toCharArray();
assertTrue('T'== chars[0]);
assertTrue('e'== chars[1]);
assertTrue('s'== chars[2]);
assertTrue('t'== chars[3]);
}
@Test
public void via_charat_2() {
char[] chars = sv.toCharsBycharat2();
assertTrue('T'== chars[0]);
assertTrue('e'== chars[1]);
assertTrue('s'== chars[2]);
assertTrue('t'== chars[3]);
}
@Test
public void via_charat() {
Character[] chars = sv.toCharsBycharat();
assertEquals(new Character('T'), chars[0]);
assertEquals(new Character('e'), chars[1]);
assertEquals(new Character('s'), chars[2]);
assertEquals(new Character('t'), chars[3]);
}
}4.2 Convert String to Char Array Java 8 Test
In this step, I will create two JUnit tests to convert a String into an array of characters.
StringToCharArray_Java8Test.java
package com.zheng.demo;
import static org.junit.Assert.assertEquals;
import org.junit.Test;
public class StringToCharArray_Java8Test {
private StringToCharArray_Java8 sv = new StringToCharArray_Java8("Test");
@Test
public void via_chars_Stream_map() {
Character[] chars = sv.toCharsByStream();
assertEquals(new Character('T'), chars[0]);
assertEquals(new Character('e'), chars[1]);
assertEquals(new Character('s'), chars[2]);
assertEquals(new Character('t'), chars[3]);
}
@Test
public void via_codePoints_Stream_map() {
Character[] chars = sv.toCharsBycodePointsStream();
assertEquals(new Character('T'), chars[0]);
assertEquals(new Character('e'), chars[1]);
assertEquals(new Character('s'), chars[2]);
assertEquals(new Character('t'), chars[3]);
}
}5. Demo
Execute mvn clean install and capture the output:
Tests Output
Build output
C:\gitworkspace\java8-demo>mvn clean install [INFO] Scanning for projects... [INFO] [INFO] ---------------------< zheng.jcg.demo:java8-demo >---------------------- [INFO] Building java8-demo 0.0.1-SNAPSHOT [INFO] --------------------------------[ jar ]--------------------------------- [INFO] [INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ java8-demo --- [INFO] Deleting C:\gitworkspace\java8-demo\target [INFO] [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ java8-demo --- [WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources,i.e. build is platform dependent! [INFO] Copying 0 resource [INFO] [INFO] --- maven-compiler-plugin:3.3:compile (default-compile) @ java8-demo --- [INFO] Changes detected - recompiling the module! [WARNING] File encoding has not been set, using platform encoding Cp1252, i.e. build is platform dependent! [INFO] Compiling 2 source files to C:\gitworkspace\java8-demo\target\classes [INFO] [INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ java8-demo --- [WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources,i.e. build is platform dependent! [INFO] Copying 0 resource [INFO] [INFO] --- maven-compiler-plugin:3.3:testCompile (default-testCompile) @ java8-demo --- [INFO] Changes detected - recompiling the module! [WARNING] File encoding has not been set, using platform encoding Cp1252, i.e. build is platform dependent! [INFO] Compiling 2 source files to C:\gitworkspace\java8-demo\target\test-classes [INFO] [INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ java8-demo --- [INFO] Surefire report directory: C:\gitworkspace\java8-demo\target\surefire-reports ------------------------------------------------------- T E S T S ------------------------------------------------------- Running com.zheng.demo.StringToCharArrayTest Tests run: 3, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.078 sec Running com.zheng.demo.StringToCharArray_Java8Test Tests run: 2, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.033 sec Results : Tests run: 5, Failures: 0, Errors: 0, Skipped: 0 [INFO] [INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ java8-demo --- [INFO] Building jar: C:\gitworkspace\java8-demo\target\java8-demo-0.0.1-SNAPSHOT.jar [INFO] [INFO] --- maven-install-plugin:2.4:install (default-install) @ java8-demo --- [INFO] Installing C:\gitworkspace\java8-demo\target\java8-demo-0.0.1-SNAPSHOT.jar to C:\repo\zheng\jcg\demo\java8-demo\0.0.1-SNAPSHOT\java8-demo-0.0.1-SNAPSHOT.jar [INFO] Installing C:\gitworkspace\java8-demo\pom.xml to C:\repo\zheng\jcg\demo\java8-demo\0.0.1-SNAPSHOT\java8-demo-0.0.1-SNAPSHOT.pom [INFO] ------------------------------------------------------------------------ [INFO] BUILD SUCCESS [INFO] ------------------------------------------------------------------------ [INFO] Total time: 5.601 s [INFO] Finished at: 2018-10-31T15:48:38-05:00 [INFO] ------------------------------------------------------------------------ C:\gitworkspace\java8-demo>
6. Summary
In this example, we demonstrated how to convert a String into a char array using Java 8 IntStream interface as well as the String class’s toCharArray method.
7. Download the Source Code
This example consists of a Maven project to convert a String object into a char array using Java 8 IntStream API.
You can download the full source code of this example here: Java 8 Convert String to Char Array Example
Last updated on Mar. 25th, 2021
This exercise is an anti-pattern.
This entire ‘tutorial’ is redundant and unnecessary — toCharArray() has been part of Java since 1.5. Exercises like this show a complete disregard for the core features of the language and encourage people to do things the hard way.
String str = “This string can be viewed as an array of chars.”;
char[] ch = str.toCharArray();
Thanks for the feedback. I did not mean creating a wrapper class for toChar. I did it because I used to the main|test class layout. In my next article, I use the test only to show the usage of the method instead of creating a class for it.
This is a neat exercise in not only different ways to perform simple things like String -> char[], but also maven and junit tests :)
This article could include some related interesting things, like how using a Stream compares to using a String class method. How does memory usage, runtime, etc compare, and why? Under what certain situations might one want to use Streams over String class methods, both for String->char[] as well as any other use cases?
Thanks for the quick read!
This no need to be a maven project right? A normal eclipse or even gradle project is ok?
Correct, you don’t need Maven for it. Any Java tool should help
Great article Mary! Actually, I like the way how Java 8 chars() method convert a string into char array! Thanks again and keep the good work!