如何通过反射访问抽象父类中的实例字段？
例如，StringBuilder 继承自抽象类AbstractStringBuilder。据我了解，StringBuilder本身没有字段（serialVersionUID除外）。相反，它的状态由 AbstractStringBuilder 中的字段表示，并通过在其重写的方法的实现中调用 super 进行操作。
有没有办法通过反射来获取与 StringBuilder 的特定实例关联的 AbstractStringBuilder 中声明的名为 value 的私有 char 数组？这是我最接近的。
import java.lang.reflect.Field;
import java.util.Arrays;
public class Test
{
public static void main(String[ ] args) throws Exception
{
StringBuilder foo = new StringBuilder("xyzzy");
Field bar = foo.getClass( ).getSuperclass( ).getDeclaredField("value");
bar.setAccessible(true);
char[ ] baz = (char[ ])bar.get(new StringBuilder( ));
}
}
这让我得到了一个包含 16 个空字符的数组。请注意，我正在寻找涉及反射的解决方案，因为我需要一种不限于 StringBuilder 的通用技术。有什么想法吗？
So, for example, StringBuilder inherits from the abstract class AbstractStringBuilder. As I understand it, StringBuilder has no fields itself (except for serialVersionUID). Rather, its state is represented by the fields in AbstractStringBuilder and manipulated by calling super in the implementations of the methods it overrides.
Is there a way via reflection to get the private char array named value declared in AbstractStringBuilder that is associated with a particular instance of StringBuilder? This is the closest I got.
import java.lang.reflect.Field;
import java.util.Arrays;
public class Test
{
public static void main(String[ ] args) throws Exception
{
StringBuilder foo = new StringBuilder("xyzzy");
Field bar = foo.getClass( ).getSuperclass( ).getDeclaredField("value");
bar.setAccessible(true);
char[ ] baz = (char[ ])bar.get(new StringBuilder( ));
}
}
That gets me an array of sixteen null characters. Note that I'm looking for solutions involving reflection, since I need a general technique that isn't limited to StringBuilder. Any ideas?
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你的问题是你正在检查一个新的 StringBuilder...所以它当然是空的（默认大小是 16 个字符）。您需要传入
fooYour problem is that you're inspecting a new StringBuilder... so of course it's empty (and 16 chars is the default size). You need to pass in
fooApache Commons BeanUtils 库可能值得一看。以下是其 API Javadocs 的链接。该库包含许多高级方法，使 Reflection 更易于使用。
It might be worth looking in the Apache Commons BeanUtils library. Here is the link to their API Javadocs. The library contains lots of high-level methods that make Reflection easier to use.