String实例在内存中分配一定数量的字节。也许您正在查看类似sizeof(“Hello World”)的东西，它将返回数据结构本身分配的字节数。

In Java, there's usually no need for a sizeof function, because we never allocate memory to store a data structure. We can have a look at the String.java file for a rough estimation, and we see some 'int', some references and a char[]. The Java language specification defines, that a char ranges from 0 to 65535, so two bytes are sufficient to keep a single char in memory. But a JVM does not have to store one char in 2 bytes, it only has to guarantee, that the implementation of char can hold values of the defines range.

sizeof在Java中没有任何意义。但是，假设我们有一个大的String并且一个char分配两个字节，那么String对象的内存占用至少是2 * str.length()字节。

迂腐的答案(虽然不一定是最有用的答案，这取决于你想对结果做什么)是:

string.length() * 2

Java字符串物理存储在UTF-16BE编码中，每个代码单元使用2个字节，而String.length()以UTF-16代码单元测量长度，因此这相当于:

final byte[] utf16Bytes= string.getBytes("UTF-16BE");
System.out.println(utf16Bytes.length);

这将告诉你内部char数组的大小，单位是字节。

注意:“UTF-16”将给出与“UTF-16BE”不同的结果，因为前者编码将插入一个BOM，将数组长度增加2个字节。

根据如何在Java中转换字符串和UTF8字节数组:

String s = "some text here";
byte[] b = s.getBytes("UTF-8");
System.out.println(b.length);

试试这个:

Bytes.toBytes(x).length

假设你之前声明并初始化了x

String实例在内存中分配一定数量的字节。也许您正在查看类似sizeof(“Hello World”)的东西，它将返回数据结构本身分配的字节数。

In Java, there's usually no need for a sizeof function, because we never allocate memory to store a data structure. We can have a look at the String.java file for a rough estimation, and we see some 'int', some references and a char[]. The Java language specification defines, that a char ranges from 0 to 65535, so two bytes are sufficient to keep a single char in memory. But a JVM does not have to store one char in 2 bytes, it only has to guarantee, that the implementation of char can hold values of the defines range.

sizeof在Java中没有任何意义。但是，假设我们有一个大的String并且一个char分配两个字节，那么String对象的内存占用至少是2 * str.length()字节。

尝试使用apache commons:

String src = "Hello"; //This will work with any serialisable object
System.out.println(
            "Object Size:" + SerializationUtils.serialize((Serializable) src).length)