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 the Field.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 a Person class that has a private field age. We can set the value of age using 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 use setAccessible(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 the Field.set() method to create a copy of the field value.

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