Array

int[] anArray = new int[10];
String[] stringArray = new String[] {"a", "b", "c" };  

List

List<String> stringList = java.util.Arrays.asList("a", "b", "c");  
List<String> stringList = java.util.Arrays.asList(array);  

Array --> List

List<String> list = java.util.Arrays.asList(array);  

List --> Array

String[] xx = list.toArray(new String[0]);  

Array --> Stream

Stream<String> stream = java.util.Arrays.stream(array);  

Stream --> Array

String[] array = stream.toArray(String[]::new);  

List --> Stream

Stream<String> stream = list.stream();  

Stream --> List

List<String> list = stream.collect(Collectors.toList());  
List<String> list = stream.toList();    // >= java 16  

Set --> Stream

Stream<String> stream = set.stream();

Stream --> Set

Set<String> set = stream.collect(toSet());

Iterate stream

stream.forEach(System.out::println);  

Create Stream

import java.nio.charset.StandardCharsets;  
import java.nio.file.Files;  
import java.nio.file.Path;  
import java.nio.file.Paths;  
import java.util.*;  
import java.util.regex.Pattern;  
import java.util.stream.*;  
  
Stream<String> stream = Stream.of("a");    >= java 1.9  
Stream<String> stream = List.of("a", "b", "c");     >= java 1.9  
Stream<String> stream = Stream.of(array);    >= java 1.9  
Stream<String> stream = Stream.<String>builder().add("a").add("b").build();  
Stream<String> stream = Stream.generate(() -> "element").limit(8);  
Stream<Integer> stream = Stream.iterate(40, n -> n + 2).limit(20);  
IntStream stream  = IntStream.range(1, 3);  
LongStream stream = LongStream.rangeClosed(1, 3);  
DoubleStream stream =  DoubleStream.of(1.0, 2.0);  
Stream<String> stream = Pattern.compile(", ").splitAsStream("a, b, c");  
  
Path path = Paths.get("c:\\file.txt");  
Stream<String> stream = Files.lines(path);  
Stream<String> stream = Files.lines(path, StandardCharsets.UTF_8);  

Stream --> XXXStream

IntStream stream = Stream.of(1, 2, 3).mapToInt(Integer::intValue);  

Stream --> parallel stream

Stream<String> stream = java.util.Arrays.asList("A", "B", "C", "D", "E").parallelStream();  
IntStream stream = java.util.stream.IntStream.rangeClosed(1, 10).parallel();  

Idiom

String string = Stream.of("apple", "take", "quiver")  
        .map(String::toUpperCase)        
        .collect(Collectors.joining(", ", "[", "]"));    
// output:  ["APPLE", "TAKE", "QUIVER"]  
  
private static Stream<String> streamOf(List<String> list){  
    return list == null || list.isEmpty() ? Stream.empty() : list.stream();
}