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)

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。

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);

如果你运行64位引用:

sizeof(string) = 
8 + // object header used by the VM
8 + // 64-bit reference to char array (value)
8 + string.length() * 2 + // character array itself (object header + 16-bit chars)
4 + // offset integer
4 + // count integer
4 + // cached hash code

换句话说:

sizeof(string) = 36 + string.length() * 2

对于32位虚拟机或64位虚拟机，如果有压缩OOPs (-XX:+UseCompressedOops)，则引用为4字节。所以总数是:

sizeof(string) = 32 + string.length() * 2

这没有考虑到对字符串对象的引用。

要避免try catch，请使用:

String s = "some text here";
byte[] b = s.getBytes(StandardCharsets.UTF_8);
System.out.println(b.length);

有一个叫做getBytes()的方法。明智地使用它。