Java .lang.String#value 从 char[]变到 byte[]有啥用意吗？

[lxk11153]

# java 8
public final class String
    implements java.io.Serializable, Comparable<String>, CharSequence {
    /** The value is used for character storage. */
    private final char value[];

# java 10
public final class String
    implements java.io.Serializable, Comparable<String>, CharSequence {
    /**
     * The value is used for character storage.
     *
     * @implNote This field is trusted by the VM, and is a subject to
     * constant folding if String instance is constant. Overwriting this
     * field after construction will cause problems.
     *
     * Additionally, it is marked with {@link Stable} to trust the contents
     * of the array. No other facility in JDK provides this functionality (yet).
     * {@link Stable} is safe here, because value is never null.
     */
    @Stable
    private final byte[] value;

ps: 不知道哪个版本变的，没去看 java 9

[shiyouming91]

Java 9 引入的 Compact Strings 。主要是为了节省内存。当构造的 String 每个字符都可以用 1 byte 表示的时候，会自动在内部存成每个字符 1 byte，不然像原来一样存成每个字符 2 bytes 。

https://www.vojtechruzicka.com/java-9-compact-strings/

[Aresxue]

更省内存呗。。。用 jol 打印下内存布局就知道，以前 Java 主要考虑易用性，现在开始优化语法糖和内存了，变成更好的语言吧

[lxk11153]

@shiyouming91 #1 那里面说的"Depending on which characters it contains, it will either use UTF-16 or Latin-1, that is - either one or two bytes per character."
是不是有点问题啊？ Latin-1: one byte per character 没问题
UTF-16 是 two bytes per character 吗？