Java Reflection Mechanism: A Comprehensive Guide

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Java Reflection Mechanism: A Comprehensive Guide

Overview

Java Reflection is a powerful mechanism that allows developers to inspect and dynamically access the properties of a class, object, or interface at runtime. In this article, we will delve into the Java java.lang.reflect.Field class, which represents a class, object, or interface attribute, and explore its methods and usage.

Java.lang.reflect.Field Class

The java.lang.reflect.Field class is used to represent a class, object, or interface attribute. It provides a way to access and manipulate the attributes of a class, including private and public attributes.

Field Object Overview

A Field object represents a single attribute of a class, object, or interface. It provides several methods to access and manipulate the attribute, including:

  • getName(): Returns the name of the attribute.
  • getType(): Returns the type of the attribute.
  • get(Object obj): Returns the value of the attribute for the specified object.
  • set(Object obj, Object value): Sets the value of the attribute for the specified object.
  • setAccessible(boolean) : Enables or disables access control permissions for the attribute.

Common Field Methods

Here are some common methods of the Field class:

Method Name Description
getName() Returns the name of the attribute.
getType() Returns the type of the attribute.
get(Object obj) Returns the value of the attribute for the specified object.
set(Object obj, Object value) Sets the value of the attribute for the specified object.
setAccessible(boolean) Enables or disables access control permissions for the attribute.

Example Code

Here is an example code snippet that demonstrates the usage of the Field class:

package com.rainmer.main;

import java.lang.reflect.Field;
import com.rainmer.bean.Book;

public class FieldTest {

    // Method to get all attributes (including private) of a class
    public void show(Class c1) {
        Field[] fi = c1.getDeclaredFields(); // Get all attributes, whether public or private
        System.out.println("~~~~~~~~~~~~ Get all have attributes (including private) ~~~~~~~~~~~~~~");
        for (Field ff : fi) {
            System.out.println(ff.getName()); // Property name
            System.out.println(ff.getType()); // Attribute type
        }
        System.out.println("~~~~~~~~~~~~ can only get common attributes ~~~~~~~~~~~~~~");
        Field[] fi1 = c1.getFields(); // Only get common attributes
        for (Field ff : fi1) {
            System.out.println(ff.getName()); // Property name
            System.out.println(ff.getType()); // Attribute type
        }
    }

    // Method to get attribute value of an object by its class
    public void show(Object ob) {
        System.out.println("~~~~~~~~~~~~~~~ acquired attribute value of the attribute and by the entity class object ~~~~~~~~~~~~~~~~~~ ~ ");
        Class cl = ob.getClass();
        Field[] fi = cl.getDeclaredFields();
        try {
            for (Field ff : fi) {
                ff.setAccessible(true); // Enable access, not the private property became common attributes
                System.out.println(ff.getName() + "value" + ff.get(ob));
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        Book bo = new Book();
        bo.setId(1);
        bo.setName("broken sky");
        bo.setType("Fantasy");
        FieldTest ft = new FieldTest();
        ft.show(Book.class);
        ft.show(bo);
    }
}

Output

SetName method called ~~~ ~~~ 
~~~~~~~~~~~~ Get all have attributes (including private) ~~~~~~~~~~~~~~
id int
name class java.lang.String
type class java.lang.String
~~~~~~~~~~~~ can only get common attributes ~~~~~~~~~~~~~~
type class java.lang.String
~~~~~~~~~~~~~~~ acquired attribute value of the attribute and by the entity class object ~~~~~~~~~~~~~~~~~~ ~ 
id value 1
name value broken sky
type value Fantasy

This code snippet demonstrates how to use the Field class to get all attributes (including private) of a class, and how to get attribute value of an object by its class.