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Java 8 UTF-16 isn't default charset but UTF-8

I been doing some coding with String in Java8,Java 11 but this question is based on Java 8. I have this little snippet.
final char e = (char)200;//È
I just thought that the characters between 0.255[Ascii+extended Ascii] would always fit in a byte just because 2^8=256 but this seems not to be true i have try on the website https://mothereff.in/byte-counter and states that the character is taking 2 bytes can somebody please explain to me.
Another question in a lot of post states that Java is UTF-16 but in my machine running Windows 7 is returning UTF-8 in this snippet.
String csn = Charset.defaultCharset().name();
Is this platform depent?
Other questions i have try this snippet.
final List<Charset>charsets = Arrays.asList(StandardCharsets.ISO_8859_1,StandardCharsets.US_ASCII,StandardCharsets.UTF_16,StandardCharsets.UTF_8);
charsets.forEach(a->print(a,"È"));
System.out.println("getBytes");
System.out.println(Arrays.toString("È".getBytes()));
charsets.forEach(a->System.out.println(a+" "+Arrays.toString(sb.toString().getBytes(a))));
private void print(final Charset set,final CharSequence sb){
byte[] array = new byte[4];
set.newEncoder()
.encode(CharBuffer.wrap(sb), ByteBuffer.wrap(array), true);
final String buildedString = new String(array,set);
System.out.println(set+" "+Arrays.toString(array)+" "+buildedString+"<<>>"+buildedString.length());
}
And prints
run:
ISO-8859-1 [-56, 0, 0, 0] È//PERFECT USING 1 BYTE WHICH IS -56
US-ASCII [0, 0, 0, 0] //DONT GET IT SEE THIS ITEM FOR LATER
UTF-16 [-2, -1, 0, -56] È<<>>1 //WHAT IS -2,-1 BYTE USED FOR? I HAVE TRY WITH OTHER EXAMPLES AND THEY ALWAYS APPEAR AM I LOSING TWO BYTES HERE??
UTF-8 [-61, -120, 0, 0] 2 È //SEEMS TO MY CHARACTER NEEDS TWO BYTES?? I THOUGHT THAT CODE=200 WOULD REQUIRE ONLY ONE
getBytes
[-61, -120]//OK MY UTF-8 REPRESENTATION
ISO-8859-1 [-56]//OK
US-ASCII [63]//OK BUT WHY WHEN I ENCODE IN ASCCI DOESNT GET ANY BYTE ENCODED?
UTF-16 [-2, -1, 0, -56]//AGAIN WHAT ARE -2,-1 IN THE LEADING BYTES?
UTF-8 [-61, -120]//OK
I have try
System.out.println(new String(new byte[]{-1,-2},"UTF-16"));//SIMPLE "" I AM WASTING THIS 2 BYTES??
In resume.
Why UTF-16 always has two leading bytes are they wasted? new byte[]{-1,-2}
Why when i encode "È" i dont get any bytes in ASCCI Charset but when i do È.getBytes(StandardCharsets.US_ASCII) i get {63}?
Java uses UTF-16 but in my case UTF-8 is platform depend??
Sorry if this post is confussing
Environment
Windows 7 64 Bits Netbeans 8.2 with Java 1.8.0_121

First question
For your first question: those bytes are the BOM code and they specify the byte order (whether the least or most significant comes first) of multibyte encoding such as UTF-16.
Second question
Every ASCII character can be encoded as a single byte in UTF-8. But ASCII is not an 8-bit encoding, it uses 7 bits for every character. And in fact, all Unicode character with code points >= 128 require at least two bytes. (The reason is that you need a way to distinguish between 200 and a multibyte code point whose first byte happens to be 200. UTF-8 solves this by using the bytes >= 128 to represent multibyte codepoints.)
'È' is not an ASCII character, so it cannot be represented in ASCII. This explains the second output: 63 is ASCII for the character '?'. And indeed, the Javadoc for the getBytes(Charset) method specifies that unmappable input is mapped to "the default replacement byte array", in this case '?'. On the other hand, to obtain the first ASCII byte array you used the CharsetEncoder directly, which is a more low-level API and does not perform such automatic replacements. (When you would have checked the result of the encode method, you would have found it to have returned a CoderResult instance representing an error.)
Third question
Java 8 Strings use UTF-16 internally, but when communicating with other software, different encodings may be expected, such as UTF-8. The Charset.defaultCharset() method returns the default character set of the virtual machine, which depends on the locale and character set of the operating system, not on the encoding used internally by Java strings.

Let's back up a bit…
Java's text datatypes use the UTF-16 character encoding of the Unicode character set. (As do, VB4/5/6/A/Script, JavaScript, .NET, ….) You can see this in the various operations you do with the string API: indexing, length, ….
Libraries support converting between the text datatypes and byte arrays using various encodings. Some of them are categorized as "Extended ASCII", but stating that is a very poor substitute for naming the character encoding actually being used.
Some operating systems allow the user to designate a default character encoding. (Most users don't know or care, though.) Java attempts to pick this up. It is only useful when the program understands that input from the user is that character encoding or that output should be. This century, users dealing in text files prefer to use a specific encoding, communicate them unchanged across systems, don't appreciate lossy conversions and therefore don't have any use for this concept. From a program's point of view, it is never what you want unless it is exactly what you want.
Where a conversion would be lossy, you have the choice of a replacement character (such a '?'), omitting it, or throwing an exception.
A character encoding is a map between a codepoint (integer) of a character set and one or more code units, according to the definition of the encoding. A code unit is a fixed size and the number of code units needed for a codepoint, might vary by codepoint.
In libraries, it is not generally useful to have an array of code units so they take the further step of converting to/from an array of bytes. byte values do range from -128 to 127, however, that's the Java interpretation as two's complement 8-bit integers. As the bytes are understood to be encoding text, the values would be interpret according to the rules of the character encoding.
Because some Unicode encodings, have code units more than one byte long, byte order becomes important. So, at the byte array level, there is UTF-16 Big Endian and UTF-16 Little Endian. When communicating a text file or stream, you would send the bytes and well as having a shared knowledge of the encoding. This "metadata" is required for understanding. So, UTF-16BE or UTF-16LE, for example. To make that a bit easier, Unicode allows some metadata beginning of the file or stream to indicate the byte order. It is called the byte-order mark (BOM) So, the external metadata can share the encoding (say, UTF-16), while the internal metadata shares the byte order. Unicode allows the BOM to be present even when byte order is not relevant, such as UTF-8. So, if the understanding is that the bytes are text encoded with any Unicode encoding and a BOM is present, then it's a very simple matter to figure out which Unicode encoding it is and what the byte order is, if relavent.
1) You are seeing the BOM in some of your Unicode encoding outputs.
2) È is not in the ASCII character set. What would want to happen in this case? I often prefer an exception.
3) The system you were using, for your account, at the time of your tests, may have had UTF-8 as the default character encoding, Is that important to the way you want and have encoded your text files on that system?

When I assign char (from literal or otherwise), what "java internal encoding is UTF16" means here? In what encoding is it stored in char?

//non-utf source file encoding
char ch = 'ё'; // some number within 0..65535 is stored in char.
System.out.println(ch); // the same number output to
"java internal encoding is UTF16". Where does it meanfully come to play in that?
Besides, I can perfectly put into char one utf16 codeunit from surrogate range (say '\uD800') - making this char perfectly invalid Unicode. And let us stay within BMP, so to avoid thinking that we might have 2 chars (codeunits) for a supplementary symbol (thinking this way sounds to me that "char internally uses utf16" is complete nonsense). But maybe "char internally uses utf16" makes sense within BMP?
I could undersand it if were like this: my source code file is in windows-1251 encoding, char literal is converted to number according to windows-1251 encoding (what really happens), then this number is automatically converted to another number (from windows-1251 number to utf-16 number) - which is NOT taking place (am I right?! this I could understand as "internally uses UTF-16"). And then that stored number is written to (really it is written as given, as from win-1251, no my "imaginary conversion from internal utf16 to output\console encoding" taking place), console shows it converting from number to glyph using console encoding (what really happens)
So this "UTF16 encoding used internally" is NEVER USED ANYHOW ??? char just stores any number (in [0..65535]), and besides specific range and being "unsigned" has NO DIFFERENCE FROM int (in scope of my example of course)???
P.S. Experimentally, code above with UTF-8 encoding of source file and console outputs
й
1081
with win-1251 encoding of source file and UTF-8 in console outputs
�
65533
Same output if we use String instead of char...
String s = "й";
System.out.println(s);
In API, all methods taking char as argument usually never take encoding as argument. But methods taking byte[] as argument often take encoding as another argument. Implying that with char we don't need encoding (meaning that we know this encoding for sure). But **how on earth do we know in what encoding something was put into char???
If char is just a storage for a number, we do need to understand what encoding this number originally came from?**
So char vs byte is just that char has two bytes of something with UNKNOWN encoding (instead of one byte of UNKNOWN encoding for a byte).
Given some initialized char variable, we don't know what encoding to use to correctly display it (to choose correct console encoding for output), we cannot tell what was encoding of source file where it was initialized with char literal (not counting cases where various encodings and utf would be compatilble).
Am I right, or am I a big idiot? Sorry for asking in latter case :)))
SO research shows no direct answer to my question:
In what encoding is a Java char stored in?
What encoding is used when I type a character?
To which character encoding (Unicode version) set does a char object
correspond?

In most cases it is best to think of a char just as a certain character (independent of any encoding), e.g. the character 'A', and not as a 16-bit value in some encoding. Only when you convert between char or a String and a sequence of bytes does the encoding play a role.
The fact that a char is internally encoded as UTF-16 is only important if you have to deal with it's numeric value.
Surrogate pairs are only meaningful in a character sequence. A single char can not hold a character value outside the BMP. This is where the character abstraction breaks down.

Unicode is system of expressing textual data as codepoints. These are typically characters, but not always. A Unicode codepoint is always represented in some encoding. The common ones are UTF-8, UTF-16 and UTF-32, where the number indicates the number of bits in a codeunit. (For example UTF-8 is encoded as 8-bit bytes, and UTF-16 is encoded as 16-bit words.)
While the first version of Unicode only allowed code points in the range 0hex ... FFFFhex, in Unicode 2.0, they changed the range to 0hex to 10FFFFhex.
So, clearly, a Java (16 bit) char is no longer big enough to represent every Unicode code point.
This brings us back to UTF-16. A Java char can represent Unicode code points that are less or equal to FFFFhex. For larger codepoints, the UTF-16 representation consists of 2 16-bit values; a so-called surrogate pair. And that will fit into 2 Java chars. So in fact, the standard representation of a Java String is a sequence of char values that constitute the UTF-16 representation of the Unicode code points.
If we are working with most modern languages (including CJK with simplified characters), the Unicode code points of interest are all found in code plane zero (0hex through FFFFhex). If you can make that assumption, then it is possible to treat a char as a Unicode code point. However, increasingly we are seeing code points in higher planes. A common case is the code points for Emojis.)
If you look at the javadoc for the String class, you will see a bunch of methods line codePointAt, codePointCount and so on. These allow you to handle text data properly ... that is to deal with the surrogate pair cases.
So how does this relate to UTF-8, windows-1251 and so on?
Well these are 8-bit character encodings that are used at the OS level in text files and so on. When you read a file using a Java Reader your text is effectively transcoded from UTF-8 (or windows-1251) into UTF-16. When you write characters out (using a Writer) you transcode in the other direction.
This doesn't always work.
Many character encodings such as windows-1251 are not capable of representing the full range of Unicode codepoints. So, if you attempt to write (say) a CJK character via a Writer configured a windows-1251, you will get ? characters instead.
If you read an encoded file using the wrong character encoding (for example, if you attempt to read a UTF-8 file as windows-1251, or vice versa) then the trancoding is liable to give garbage. This phenomenon is so common it has a name: Mojibake).
You asked:
Does that mean that in char ch = 'й'; literal 'й' is always converted to utf16 from whatever encoding source file was in?
Now we are (presumably) talking about Java source code. The answer is that it depends. Basically, you need to make sure that the Java compiler uses the correct encoding to read the source file. This is typically specified using the -encoding command line option. (If you don't specify the -encoding then the "platform default converter" is used; see the javac manual entry.)
Assuming that you compile your source code with the correct encoding (i.e. matching the actual representation in the source file), the Java compiler will emit code containing the correct UTF-16 representation of any String literals.
However, note that this is independent of the character encoding that your application uses to read and write files at runtime. That encoding is determined by what your application selects or the execution platform's default encoding.

Is there a drastic difference between UTF-8 and UTF-16

I call a webservice, that gives me back a response xml that has UTF-8 encoding. I checked that in java using getAllHeaders() method.
Now, in my java code, I take that response and then do some processing on it. And later, pass it on to a different service.
Now, I googled a bit and found out that by default the encoding in Java for strings is UTF-16.
In my response xml, one of the elements had a character É. Now this got screwed in the post processing request that I make to a different service.
Instead of sending É, it sent some jibberish stuff. Now I wanted to know, will there be really a lot of difference in the two of these encodings? And if I wanted to know what will É convert from UTF-8 to UTF-16, then how can I do that?

Both UTF-8 and UTF-16 are variable length encodings. However, in UTF-8 a character may occupy a minimum of 8 bits, while in UTF-16 character length starts with 16 bits.
Main UTF-8 pros:
Basic ASCII characters like digits, Latin characters with no
accents, etc. occupy one byte which is identical to US-ASCII
representation. This way all US-ASCII strings become valid UTF-8,
which provides decent backwards compatibility in many cases.
No null bytes, which allows to use null-terminated strings, this
introduces a great deal of backwards compatibility too.
Main UTF-8 cons:
Many common characters have different length, which slows indexing
and calculating a string length terribly.
Main UTF-16 pros:
Most reasonable characters, like Latin, Cyrillic, Chinese, Japanese
can be represented with 2 bytes. Unless really exotic characters are
needed, this means that the 16-bit subset of UTF-16 can be used as a
fixed-length encoding, which speeds indexing.
Main UTF-16 cons:
Lots of null bytes in US-ASCII strings, which means no
null-terminated strings and a lot of wasted memory.
In general, UTF-16 is usually better for in-memory representation while UTF-8 is extremely good for text files and network protocol

There are two things:
the encoding in which you exchange data;
the internal string representation of Java.
You should not be preoccupied with the second point ;) The thing is to use the appropriate methods to convert from your data (byte arrays) to Strings (char arrays ultimately), and to convert form Strings to your data.
The most basic classes you can think of are CharsetDecoder and CharsetEncoder. But there are plenty others. String.getBytes(), all Readers and Writers are but two possible methods. And there are all static methods of Character as well.
If you see gibberish at some point, it means you failed to decode or encode from the original byte data to Java strings. But again, the fact that Java strings use UTF-16 is not relevant here.
In particular, you should be aware that when you create a Reader or Writer, you should specify the encoding; if you fail to do so, the default JVM encoding will be used, and it may, or may not, be UTF-8.

This Website provide UTF TO UTF Conversion
http://www.fileformat.info/convert/text/utf2utf.htm
UTF-32 is arguably the most human-readable of the Unicode Encoding Forms, because its big-endian hexadecimal representation is simply the Unicode Scalar Value without the “U+” prefix and zero-padded to eight digits and While a UTF-32 representation does make the programming model somewhat simpler, the increased average storage size has real drawbacks, making a complete transition to UTF-32 less compelling.
HOWEVER
UTF-32 is the same as the old UCS-4 encoding and remains fixed width. Why can this remain fixed width? As UTF-16 is now the format that can encode the least amount of characters it set the limit for all formats. It was defined that 1,112,064 was the total number of code points that will ever be defined by either Unicode or ISO 10646. Since Unicode is now only defined from 0 to 10FFFF UTF-32 sounds a bit like a pointless encoding now as it's 32 bit wide, but only ever about 21 bits are used which makes this very wasteful.

UTF-8: Generally speaking, you should use UTF-8. Most HTML documents use this encoding.
It uses at least 8 bits of data to store each character. This can lead to more efficient storage, especially when the text contains mostly English ASCII characters. But higher-order characters, such as non-ASCII characters, may require up to 24 bits each!
UTF-16:
This encoding uses at least 16 bits to encode characters, including lower-order ASCII characters and higher-order non-ASCII characters.
If you are encoding text consisting of mostly non-English or non-ASCII characters, UTF-16 may result in smaller file size. But if you use UTF-16 to encode mostly ASCII text, it will use up more space.

Isn't the size of character in Java 2 bytes?

I used RandomAccessFile to read a byte from a text file.
public static void readFile(RandomAccessFile fr) {
byte[] cbuff = new byte[1];
fr.read(cbuff,0,1);
System.out.println(new String(cbuff));
}
Why am I seeing one full character being read by this?

A char represents a character in Java (*). It is 2 bytes large (or 16 bits).
That doesn't necessarily mean that every representation of a character is 2 bytes long. In fact many character encodings only reserve 1 byte for every character (or use 1 byte for the most common characters).
When you call the String(byte[]) constructor you ask Java to convert the byte[] to a String using the platform's default charset(**). Since the platform default charset is usually a 1-byte encoding such as ISO-8859-1 or a variable-length encoding such as UTF-8, it can easily convert that 1 byte to a single character.
If you run that code on a platform that uses UTF-16 (or UTF-32 or UCS-2 or UCS-4 or ...) as the platform default encoding, then you will not get a valid result (you'll get a String containing the Unicode Replacement Character instead).
That's one of the reasons why you should not depend on the platform default encoding: when converting between byte[] and char[]/String or between InputStream and Reader or between OutputStream and Writer, you should always specify which encoding you want to use. If you don't, then your code will be platform-dependent.
(*) that's not entirely true: a char represents a UTF-16 code unit. Either one or two UTF-16 code units represent a Unicode code point. A Unicode code point usually represents a character, but sometimes multiple Unicode code points are used to make up a single character. But the approximation above is close enough to discuss the topic at hand.
(**) Note that on Android the default character set is always UTF-8 and starting with Java 18 the Java platform itself also switched to this default (but it can still be configured to act the legacy way)

Java stores all it's "chars" internally as two bytes. However, when they become strings etc, the number of bytes will depend on your encoding.
Some characters (ASCII) are single byte, but many others are multi-byte.
Java supports Unicode, thus according to:
Java Character Docs
The max value supported is "\uFFFF" (hex FFFF, dec 65535), or 11111111 11111111 binary (two bytes).

The constructor String(byte[] bytes) takes the bytes from the buffer and encodes them to characters.
It uses the platform default charset to encode bytes to characters. If you know, your file contains text, that is encoded in a different charset, you can use the String(byte[] bytes, String charsetName) to use the correct encoding (from bytes to characters).

In ASCII text file each character is just one byte

Looks like your file contains ASCII characters, which are encoded in just 1 byte. If text file was containing non-ASCII character, e.g. 2-byte UTF-8, then you get just the first byte, not whole character.

There are some great answers here but I wanted to point out the jvm is free to store a char value in any size space >= 2 bytes.
On many architectures there is a penalty for performing unaligned memory access so a char might easily be padded to 4 bytes. A volatile char might even be padded to the size of the CPU cache line to prevent false sharing. https://en.wikipedia.org/wiki/False_sharing
It might be non-intuitive to new Java programmers that a character array or a string is NOT simply multiple characters. You should learn and think about strings and arrays distinctly from "multiple characters".
I also want to point out that java characters are often misused. People don't realize they are writing code that won't properly handle codepoints over 16 bits in length.

Java allocates 2 of 2 bytes for character as it follows UTF-16. It occupies minimum 2 bytes while storing a character, and maximum of 4 bytes. There is no 1 byte or 3 bytes of storage for character.

The Java char is 2 bytes. But the file encoding may be different.
So first you should know what encoding your file uses. For example, the file could be UTF-8 or ASCII encoded, then you will retrieve the right chars by reading one byte at a time.
If the encoding of the file is UTF-16, it may still show you the correct char if your UTF-16 is little endian. For example, the little endian UTF-16 for A is [65, 0]. Then when you read the first byte, it returns 65. After padding with 0 for the second byte, you will get A.

Difference between UTF-8 and UTF-16?

Difference between UTF-8 and UTF-16?
Why do we need these?
MessageDigest md = MessageDigest.getInstance("SHA-256");
String text = "This is some text";
md.update(text.getBytes("UTF-8")); // Change this to "UTF-16" if needed
byte[] digest = md.digest();

I believe there are a lot of good articles about this around the Web, but here is a short summary.
Both UTF-8 and UTF-16 are variable length encodings. However, in UTF-8 a character may occupy a minimum of 8 bits, while in UTF-16 character length starts with 16 bits.
Main UTF-8 pros:
Basic ASCII characters like digits, Latin characters with no accents, etc. occupy one byte which is identical to US-ASCII representation. This way all US-ASCII strings become valid UTF-8, which provides decent backwards compatibility in many cases.
No null bytes, which allows to use null-terminated strings, this introduces a great deal of backwards compatibility too.
UTF-8 is independent of byte order, so you don't have to worry about Big Endian / Little Endian issue.
Main UTF-8 cons:
Many common characters have different length, which slows indexing by codepoint and calculating a codepoint count terribly.
Even though byte order doesn't matter, sometimes UTF-8 still has BOM (byte order mark) which serves to notify that the text is encoded in UTF-8, and also breaks compatibility with ASCII software even if the text only contains ASCII characters. Microsoft software (like Notepad) especially likes to add BOM to UTF-8.
Main UTF-16 pros:
BMP (basic multilingual plane) characters, including Latin, Cyrillic, most Chinese (the PRC made support for some codepoints outside BMP mandatory), most Japanese can be represented with 2 bytes. This speeds up indexing and calculating codepoint count in case the text does not contain supplementary characters.
Even if the text has supplementary characters, they are still represented by pairs of 16-bit values, which means that the total length is still divisible by two and allows to use 16-bit char as the primitive component of the string.
Main UTF-16 cons:
Lots of null bytes in US-ASCII strings, which means no null-terminated strings and a lot of wasted memory.
Using it as a fixed-length encoding “mostly works” in many common scenarios (especially in US / EU / countries with Cyrillic alphabets / Israel / Arab countries / Iran and many others), often leading to broken support where it doesn't. This means the programmers have to be aware of surrogate pairs and handle them properly in cases where it matters!
It's variable length, so counting or indexing codepoints is costly, though less than UTF-8.
In general, UTF-16 is usually better for in-memory representation because BE/LE is irrelevant there (just use native order) and indexing is faster (just don't forget to handle surrogate pairs properly). UTF-8, on the other hand, is extremely good for text files and network protocols because there is no BE/LE issue and null-termination often comes in handy, as well as ASCII-compatibility.

They're simply different schemes for representing Unicode characters.
Both are variable-length - UTF-16 uses 2 bytes for all characters in the basic multilingual plane (BMP) which contains most characters in common use.
UTF-8 uses between 1 and 3 bytes for characters in the BMP, up to 4 for characters in the current Unicode range of U+0000 to U+1FFFFF, and is extensible up to U+7FFFFFFF if that ever becomes necessary... but notably all ASCII characters are represented in a single byte each.
For the purposes of a message digest it won't matter which of these you pick, so long as everyone who tries to recreate the digest uses the same option.
See this page for more about UTF-8 and Unicode.
(Note that all Java characters are UTF-16 code points within the BMP; to represent characters above U+FFFF you need to use surrogate pairs in Java.)

Security: Use only UTF-8
Difference between UTF-8 and UTF-16? Why do we need these?
There have been at least a couple of security vulnerabilities in implementations of UTF-16. See Wikipedia for details.
CVE-2008-2938
CVE-2012-2135
WHATWG and W3C have now declared that only UTF-8 is to be used on the Web.
The [security] problems outlined here go away when exclusively using UTF-8, which is one of the many reasons that is now the mandatory encoding for all things.
Other groups are saying the same.
So while UTF-16 may continue being used internally by some systems such as Java and Windows, what little use of UTF-16 you may have seen in the past for data files, data exchange, and such, will likely fade away entirely.

This is unrelated to UTF-8/16 (in general, although it does convert to UTF16 and the BE/LE part can be set w/ a single line), yet below is the fastest way to convert String to byte[]. For instance: good exactly for the case provided (hash code). String.getBytes(enc) is relatively slow.
static byte[] toBytes(String s){
byte[] b=new byte[s.length()*2];
ByteBuffer.wrap(b).asCharBuffer().put(s);
return b;
}

Simple way to differentiate UTF-8 and UTF-16 is to identify commonalities between them.
Other than sharing same unicode number for given character, each one is their own format.
UTF-8 try to represent, every unicode number given to character with one byte(If it is ASCII), else 2 two bytes, else 4 bytes and so on...
UTF-16 try to represent, every unicode number given to character with two byte to start with. If two bytes are not sufficient, then uses 4 bytes. IF that is also not sufficient, then uses 6 bytes.
Theoretically, UTF-16 is more space efficient, but in practical UTF-8 is more space efficient as most of the characters(98% of data) for processing are ASCII and UTF-8 try to represent them with single byte and UTF-16 try to represent them with 2 bytes.
Also, UTF-8 is superset of ASCII encoding. So every app that expects ASCII data would also accepted by UTF-8 processor. This is not true for UTF-16. UTF-16 could not understand ASCII, and this is big hurdle for UTF-16 adoption.
Another point to note is, all UNICODE as of now could be fit in 4 bytes of UTF-8 maximum(Considering all languages of world). This is same as UTF-16 and no real saving in space compared to UTF-8 ( https://stackoverflow.com/a/8505038/3343801 )
So, people use UTF-8 where ever possible.