How does Java reflection mechanism set field values?

Use reflection mechanism to set field value: get field reference through Field.getDeclaredField(). Call the Field.set() method to set the target object's new value.

Java reflection mechanism: setting field values

The reflection mechanism is a way to check and modify classes, methods, and fields at runtime Mechanisms. It allows us to access, set or call private or protected members of a Java program.

Set field value

To set the field value, we can use theField.set()method. This method accepts two parameters:

• Target object
• New value to be set

Syntax:

field.set(目标对象, 新值);

Code Example:

Suppose we have aPersonclass that has a private fieldage. We can set the value ofageusing the following code:

import java.lang.reflect.Field; public class Main { public static void main(String[] args) throws Exception { // 实例化 Person 对象 Person person = new Person(); // 获取 Person 类的私有字段 age Field field = person.getClass().getDeclaredField("age"); // 将 age 的值设置为 30 field.set(person, 30); // 输出 age 的值 System.out.println(person.getAge()); // 输出：30 } } class Person { private int age; public int getAge() { return age; } public void setAge(int age) { this.age = age; } }

Note:

• To access private fields we need to usesetAccessible(true)Method removes the privacy of a field.
• You can also set protected or package access fields.
• If you do not want to modify the original object, you can also use theField.set()method to create a copy of the field value.

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