使用反射时的Java NoSuchFieldError [英] Java NoSuchFieldError when using Reflection

问题描述

我正在尝试修改我在ClassA中创建的公共静态最终String []字段，然后使用反射在ClassB中对其进行修改.但是我得到了NoSuchFieldException.

  java.lang.NoSuchFieldException:测试在java.lang.Class.getField(未知来源)在packageA.ClassA.< init>(ClassA.java:17) 

ClassA 位于 packageA 中，而 ClassB 位于 packageB 中.

Class A ，创建该字段并调用 ClassB :

  package packageA;导入packageB.ClassB;公共类ClassA {//创建最终的String []public static final String [] test = new String [] {"Test1"，"Test2"，"Test3"};公共ClassA(){//更改前输出数组内容for(int i = 0; i< test.length; i ++){System.out.println(test [i]);}//更改数组内容尝试 {新的ClassB(String [].class.getField("test")，新的String [] {"Change1"，"Change2"，"Change3"}));} catch(Exception e){e.printStackTrace();}//更改后输出数组内容for(int i = 0; i< test.length; i ++){System.out.println(test [i]);}}} 

B类，修改测试"数组:

  package packageB;导入java.lang.reflect.Field;导入java.lang.reflect.Modifier;公共课程ClassB {公共ClassB(Field field，Object newValue){尝试 {field.setAccessible(true);字段修饰符Field = Field.class.getDeclaredField("modifiers");ModifiersField.setAccessible(true);ModifysField.setInt(field，field.getModifiers()&〜Modifier.FINAL);field.set(null，newValue);} catch(Exception e){e.printStackTrace();}}} 

注意:我从此处获得了ClassB，还看到了这篇帖子，但我找不到任何有效的方法.

根据我从该主题收集的信息，我认为异常表示它不知道ClassB中的测试"是什么，并且我还没有在ClassB中对其进行初始化，但是我真的无法弄清楚.

解决方案

String [].class.getField("test")引发 NoSuchFieldException ，因为此字段确实 String [] 中不存在，而在 packageA.ClassA 中存在.

ClassA.class.getField("test")将返回正确的字段访问.

I'm trying to modify a public static final String[] field I made in ClassA, and then modify it in ClassB using reflection. However I get a NoSuchFieldException.

java.lang.NoSuchFieldException: test
at java.lang.Class.getField(Unknown Source)
at packageA.ClassA.<init>(ClassA.java:17)

ClassA is located in packageA and ClassB is located in packageB if that matters.

Class A, creates the field and calls ClassB:

package packageA;

import packageB.ClassB;

public class ClassA {
    // Create final String[]
    public static final String[] test = new String[] {"Test1", "Test2", "Test3"};

    public ClassA() {
        // Output array content before change
        for (int i = 0; i < test.length; i++) {
            System.out.println(test[i]);
        }

        // Change array content
        try {
            new ClassB(String[].class.getField("test"), new String[] {"Change1", "Change2", "Change3"});
        } catch (Exception e) {
            e.printStackTrace();
        }

        // Output array content after change
        for (int i = 0; i < test.length; i++) {
            System.out.println(test[i]);
        } 
    }
}

Class B, Modifies the 'test' array:

package packageB;

import java.lang.reflect.Field;
import java.lang.reflect.Modifier;

public class ClassB {

    public ClassB(Field field, Object newValue) {
        try {
            field.setAccessible(true);

            Field modifiersField = Field.class.getDeclaredField("modifiers");
            modifiersField.setAccessible(true);
            modifiersField.setInt(field, field.getModifiers() & ~Modifier.FINAL);

            field.set(null, newValue);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Note: I got ClassB from here and I also saw this post but I couldn't find anything that worked.

From what i've gathered from that topic, I think the exception means that it doesn't know what 'test' is in ClassB and that I haven't initialized it in ClassB, but I couldn't really figure that out.

解决方案

String[].class.getField("test") throws a NoSuchFieldException because this field does not exist in String[], it exists in packageA.ClassA.

ClassA.class.getField("test") will return the correct field access.

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