reflex

With reflection, you can directly obtain the type, attribute and method in the class bytecode file.

Demo code:

Create a new class named User as the reflecting operation object

public class User {
    private int id;
    private String name;
    private String password;
    public User() {
    
    }
    /**
     * @return the id
     */
    public int getId() {
        return id;
    }
    /**
     * @return the name
     */
    public String getName() {
        return name;
    }
    /**
     * @return the password
     */
    public String getPassword() {
        return password;
    }
    /**
     * @param id the id to set
     */
    public void setId(int id) {
        this.id = id;
    }
    /**
     * @param name the name to set
     */
    public void setName(String name) {
        this.name = name;
    }
    /**
     * @param password the password to set
     */
    public void setPassword(String password) {
        this.password = password;
    }
    /* (non-Javadoc)
     * @see java.lang.Object#toString()
     */
    @Override
    public String toString() {
        return "User [id=" + id + ", name=" + name + ", password=" + password + "]";
    }
    
    
}

Demonstration

class

Acquisition class

Object u = new User();
Class class1 = u.getClass();

Get class name

class1.getName()

Get class access

int modifier = class1.getModifiers();
boolean flag = Modifier.isPublic(modifier);
System.out.println("yes public？: "+flag);

attribute

Get all properties of the class
Access to private can also be obtained

Field[] arr = class1.getDeclaredFields();
for (Field field:arr) {
    System.out.println ("Properties in class:" + field);
}

Get the value of all properties of the class
Private properties cannot be obtained by default, but can be obtained directly without checking access rights.

// Get values for all properties
for (Field field:arr) {
    // Do not check access rights
    field.setAccessible(true);
    // Get the value of field in u object
    Object o = field.get(u);
    System.out.println("Property values in class:" +o);
}

Specify property name to get property

Field f = class1.getDeclaredField("name");
f.setAccessible(true);
f.set(u, "Zhang San");
Object o = f.get(u);
System.out.println("name: " + o);

Method

Get all methods (including methods inherited from the parent class)

Method[] allMethods = class1.getMethods();
System.out.println("All methods of class:");
for (Method method:allMethods) {
    System.out.println(method);
}

Get the class's own methods

Method[] onlyMethods = class1.getDeclaredMethods();
for (Method method:onlyMethods) {
    System.out.println(method);
}

Call the return value method without parameters

Method method2 = class1.getDeclaredMethod("getName");
String str = (String)(method2.invoke(u));
System.out.println ("Return value:"+ str);

Call method with parameter and no return value

Method method = class1.getDeclaredMethod("setName", String.class);
method.invoke(u, "Li Si");

Full demo code:

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

public class ReflectTest {
    public static void main(String[] args) throws IllegalArgumentException, IllegalAccessException, NoSuchFieldException, SecurityException, NoSuchMethodException, InvocationTargetException {
        Object u = new User();
        // Get class to User
        Class class1 = u.getClass();
        
        System.out.println("Class name:"+class1.getName());
        
        // Get class access
        int modifier = class1.getModifiers();
        boolean flag = Modifier.isPublic(modifier);
        System.out.println("yes public？: "+flag);
        
        // Get all properties
        Field[] arr = class1.getDeclaredFields();
        for (Field field:arr) {
            System.out.println ("Properties in class:" + field);
        }
        // Get values for all properties
        for (Field field:arr) {
            // Do not check access rights
            field.setAccessible(true);
            // Get the value of field in u object
            Object o = field.get(u);
            System.out.println("Property values in class:" +o);
        }
        
        // Specify the field name to get the property
        Field f = class1.getDeclaredField("name");
        f.setAccessible(true);
        f.set(u, "Zhang San");
        Object o = f.get(u);
        System.out.println("name: " + o);
        
        // Get all methods (including inheritance methods)
        Method[] allMethods = class1.getMethods();
        System.out.println("All methods of class:");
        for (Method method:allMethods) {
            System.out.println(method);
        }
        // Get the current class's own methods
        Method[] onlyMethods = class1.getDeclaredMethods();
        for (Method method:onlyMethods) {
            System.out.println(method);
        }
        
        // Call a parameterized method
        Method method = class1.getDeclaredMethod("setName", String.class);
        method.invoke(u, "Li Si");
        
        // Call no parameter return value method
        Method method2 = class1.getDeclaredMethod("getName");
        String str = (String)(method2.invoke(u));
        System.out.println ("Return value:"+ str);
        
    }

}