访问Java的私有字段

Question

javax.swing.text.html.ImageView; lines 111 and 258-267
http://javasourcecode.org/html/open-source/jdk/jdk-6u23/javax/swing/text/html/ImageView.java.html

public class ImageView extends View {
    ....
    private float vAlign;
    ....
}

My program:

.....
ImageView layeredPane = (ImageView) view;
Field privateStringField = layeredPane.getClass().getDeclaredField("vAlign");
privateStringField.setAccessible(true);
layeredPane.vAlign = 2.0;
.....

I get:

Test.java:80: error: vAlign has private access in ImageView layeredPane.vAlign = 2.0;

How do I fix it? I need to put a value of 2.0

Answer 1

You fix it by not trying to get at private implementation details. Basically you shouldn't be doing this. Your code will end up being brittle even when you're still using this version of ImageView , and vulnerable to changes between versions. The whole point of it being private is to stop you from accessing it directly.

You can fall privateStringField.setFloat(layeredPane, 2.0f) but I would strongly advise against it.

(It's odd to call it privateStringField when it's a float field, by the way...)

Answer 2

First off, why would you want to use 2.0? I thought that the vAlign uses the java.awt.Component contants for BOTTOM_ALIGNMENT, CENTER_ALIGNMENT AND TOP_ALIGNMENT which hold 1.0f, 0.5f, and 0.0f respectively, and so a value of 2.0 may not make much sense.

Regardless, since it's a private field, don't fiddle with it directly and change it via appropriate means. It appears that this private field is set via attributes:

Object alignment = attr.getAttribute(HTML.Attribute.ALIGN);