How to "split" and "join" string in java

Question

in javascript, we can turn a string to an array by using "split" method.
exampel :
var a = "Hello world";
var b = a.split('');

document.write(b);

//output = H,e,l,l,o, ,w,o,r,l,d

or join method :
var a = [1,2,3,4,5,6,7];
var b = a.join('');

document.write(b);

//output = 1234567

what method should i use to Split or Join string in Java ??

Answer 1

"thing".split("")
String.join("", array)

Answer 2

public void whenJoiningTwoArrays_thenJoined() {
String[] animals1 = new String[] { "Dog", "Cat" };
String[] animals2 = new String[] { "Bird", "Cow" };

String[] result = Stream.concat(
Arrays.stream(animals1), Arrays.stream(animals2)).toArray(String[]::new);

assertArrayEquals(result, new String[] { "Dog", "Cat", "Bird", "Cow" });
}