How to join arrays in Java

In this post, we are going to learn to join multiple arrays into a single array using the Java code. There can be a scenario when we need to combine data of two or more arrays into a single array such as combining two sources into one to transport the data as a single source.

Here, we are using Java 8 stream API to joins arrays and get a result as an array or stream. See the given examples here.

Time for an Example:

Let's take an example to join two string arrays into a single string array. Here, we are using of() method of Stream that returns a sequence of stream which further is converted into array by using the toArray() method.

import java.util.stream.Stream;
public class Main {
	public static void main(String[] args){  
		String[] asia = new String[]{"India", "Russia", "Japan"};
        String[] europe = new String[]{"Poland", "Germany", "France"};

		//join arrays
        String[] countries = Stream.of(asia,europe).flatMap(Stream::of).toArray(String[]::new);
        for (String country : countries) {
			System.out.println(country);
		}
	}
}

India
Russia
Japan
Poland
Germany
France

Time for another Example:

We can combine two streams by using the concat() method that returns a stream of specified type. The example explains how we can concat two or more stream into a single stream as we did in the above example to combine two arrays.

import java.util.stream.Stream;
public class Main {
	public static void main(String[] args){  
		Stream<Integer> stream1 = Stream.of(1, 2, 3);
	    Stream<Integer> stream2 = Stream.of(4, 5, 6);
	    //concat arrays
	    Stream<Integer> result = Stream.concat(stream1, stream2);
	    result.forEach(System.out::println);
	}
}

1
3
5
2
4
6