In this tutorial we will go over different ways we can join Java Arrays.
If you have any of below questions then you are at right place:
- How can I concatenate two arrays in Java?
- How to Merge Two Arrays in Java?
- 3 Ways to Combine Arrays in Java
- Join Array of Primitives with Separator in Java
Here are the three ways you could you could join arrays in Java.
- Join Array using Apache Common utility
- Join Array using Java8 Stream operation
- Join Array using Standard Java APIs
Let’s get started:
Create java class CrunchifyJoinArrays3Ways.java.
Put below Java code into file.
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package crunchify.com.tutorial; import org.apache.commons.lang3.ArrayUtils; import java.lang.reflect.Array; import java.util.Arrays; import java.util.stream.IntStream; import java.util.stream.Stream; /** * @author Crunchify.com * <p> * In Java how to join Arrays? 3 ways: Apache Commons ArrayUtils, Java 8 Streams and Simple APIs. * Version: 1.0.3 */ public class CrunchifyJoinArrays3Ways { public static void main(String[] args) { crunchifyPrint("Original String Array1: [google, twitter]"); crunchifyPrint("Original String Array2: [apple, microsoft]"); crunchifyPrint("Original Integer Array1: [111, 444]"); crunchifyPrint("Original Integer Array2: [222, 555]\n"); // Join Array using Apache Common utility joinArrayUsingApacheCommon(); // Join Array using Java8 Stream operation joinArrayUsingJava8Stream(); // Join Array using Standard Java APIs joinArrayUsingJavaAPI(); } // Method-1: Join Array using Apache Common utility private static void joinArrayUsingApacheCommon() { String[] company1 = new String[]{"google", "twitter"}; String[] company2 = new String[]{"apple", "microsoft"}; // from org.apache.commons.lang3 maven dependency String[] crunchifyResult = ArrayUtils.addAll(company1, company2); crunchifyPrint("From Method-1: addAll() - String ==> " + Arrays.toString(crunchifyResult)); int[] crunchifyArray1 = new int[]{111, 444}; int[] crunchifyArray2 = new int[]{222, 555}; int[] crunchifyResult2 = ArrayUtils.addAll(crunchifyArray1, crunchifyArray2); crunchifyPrint("From Method-1: addAll() - Integer ==> " + Arrays.toString(crunchifyResult2)); } // Simple Java Print Method private static void crunchifyPrint(String result) { System.out.println(result); } // Method-2: Join Array using Java8 Stream operation private static void joinArrayUsingJava8Stream() { String[] company1 = new String[]{"google", "twitter"}; String[] company2 = new String[]{"apple", "microsoft"}; // Stream.of() - returns a sequential ordered stream whose elements are the specified values. // A sequence of elements supporting sequential and parallel aggregate operations. The following example illustrates an aggregate operation using Stream and IntStream: // // int sum = widgets.stream() // .filter(w -> w.getColor() == RED) // .mapToInt(w -> w.getWeight()) // .sum(); String[] result = Stream.of(company1, company2).flatMap(Stream::of).toArray(String[]::new); crunchifyPrint("\nFrom Method-2: Stream.of() ==> " + Arrays.toString(result)); int[] crunchifyArray1 = new int[]{111, 444}; int[] crunchifyArray2 = new int[]{222, 555}; // Arrays.stream() - returns a sequential IntStream with the specified array as its source. int[] crunchifyResult2 = IntStream.concat(Arrays.stream(crunchifyArray1), Arrays.stream(crunchifyArray2)).toArray(); crunchifyPrint("From Method-2: IntStream.concat() ==> " + Arrays.toString(crunchifyResult2)); } // Method-3: Join Array using Standard Java APIs private static void joinArrayUsingJavaAPI() { String[] company1 = new String[]{"google", "twitter"}; String[] company2 = new String[]{"apple", "microsoft"}; String[] crunchifyResult = crunchifyJoinGenericArray(company1, company2); crunchifyPrint("\nFrom Method-3: crunchifyJoinArrayusingGeneric() ==> " + Arrays.toString(crunchifyResult)); int[] crunchifyArray1 = new int[]{111, 444}; int[] crunchifyArray2 = new int[]{222, 555}; int[] crunchifyResult2 = crunchifyJoinIntegerArray(crunchifyArray1, crunchifyArray2); // Arrays.toString() Returns a string representation of the contents of the specified array. // The string representation consists of a list of the array's elements, enclosed in square brackets ("[]"). // Adjacent elements are separated by the characters ", " (a comma followed by a space). // Elements are converted to strings as by String.valueOf(int). Returns "null" if a is null. crunchifyPrint("From Method-3: joinArray() ==> " + Arrays.toString(crunchifyResult2)); } @SafeVarargs private static <T> T[] crunchifyJoinGenericArray(T[]... crunchifyArrays) { int crunchify = 0; for (T[] crunchifyArray : crunchifyArrays) { crunchify += crunchifyArray.length; } //T[] result = new T[crunchify]; final T[] crunchifyResult = (T[]) Array.newInstance(crunchifyArrays[0].getClass().getComponentType(), crunchify); int crunchifyOffset = 0; for (T[] crunchifyArray : crunchifyArrays) { // Copies an array from the specified source array, beginning at the specified position, to the specified position of the destination array. // A subsequence of array components are copied from the source array referenced by src to the destination array referenced by dest. // The number of components copied is equal to the length argument. // The components at positions srcPos through srcPos+length-1 in the source array are copied into positions destPos through destPos+length-1, respectively, of the destination array. System.arraycopy(crunchifyArray, 0, crunchifyResult, crunchifyOffset, crunchifyArray.length); crunchifyOffset += crunchifyArray.length; } return crunchifyResult; } private static int[] crunchifyJoinIntegerArray(int[]... crunchifyArrays) { int crunchify = 0; for (int[] crunchifyArray : crunchifyArrays) { crunchify += crunchifyArray.length; } final int[] crunchifyResult = new int[crunchify]; int crunchifyOffset = 0; for (int[] crunchifyArray : crunchifyArrays) { System.arraycopy(crunchifyArray, 0, crunchifyResult, crunchifyOffset, crunchifyArray.length); crunchifyOffset += crunchifyArray.length; } return crunchifyResult; } } |
Let’s take a look at some of Java API details.
java.lang.System.arraycopy():
java.util.Arrays.toString():
java.util.stream():
Just run program as a Java Program and you should see a result same as below.
IntelliJ IDEA console output:
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/Library/Java/JavaVirtualMachines/jdk-15.jdk/Contents/Home/bin/java -javaagent:/Applications/IntelliJ IDEA.app/Contents/lib/idea_rt.jar=50249:/Applications/IntelliJ IDEA.app/Contents/bin -Dfile.encoding=UTF-8 -classpath /Users/app/crunchify/github/CrunchifyTutorials/target/classes:/Users/app/crunchify/github/CrunchifyTutorials/WebContent/WEB-INF/lib/zxing-2.1.jar/Users/app/.m2/repository/commons-collections/commons-collections/3.2.1/commons-collections-3.2.1.jar/spring-context-support-5.1.3.RELEASE.jar crunchify.com.tutorial.CrunchifyJoinArrays3Ways Original String Array1: [google, twitter] Original String Array2: [apple, microsoft] Original Integer Array1: [111, 444] Original Integer Array2: [222, 555] From Method-1: addAll() - String ==> [google, twitter, apple, microsoft] From Method-1: addAll() - Integer ==> [111, 444, 222, 555] From Method-2: Stream.of() ==> [google, twitter, apple, microsoft] From Method-2: IntStream.concat() ==> [111, 444, 222, 555] From Method-3: crunchifyJoinArrayusingGeneric() ==> [google, twitter, apple, microsoft] From Method-3: joinArray() ==> [111, 444, 222, 555] Process finished with exit code 0 |
Please let me know if you have any other way to merge Java Arrays or you get any exception.