Reflection advanced explanation

Warm reminder: if you don't know much about reflection, you can go to a few introductory articles to learn more!

Review:

Why reflection: call private content in a class at will. Class is more flexible.   Reflection: get a member method / member variable in a class specifically   Reflection fixation steps: Obtain Get Class object Class Get content through class objects (member methods, member variables) Set available out of class (violent reflection, private) implement 2.1. Obtain the construction method of class through class object 2.2. Creating objects by construction method 2.3. Call Get member method: getMethod gets the public method in the current class or parent class getDeclaredMethod gets any method of the current class (regardless of the access modifier) Get member variable: getField gets the public field in the current class or parent class getDeclaredField gets any field of the current class (regardless of the access modifier)     Executive member method: Object obj = method object. Invoke (object, parameter 1, parameter 2 );   Execute member variable: field object. set assignment field object. get value

1, Advanced case 1: execute public method

Code implementation:
/*
*   Execute the public method:
*                   getDeclaredMethod   Get any method in the current class (ignoring the access modifier), which is suitable for reflection calling the current class method
*                   getMethod           The current class or parent class obtains the public method, which is suitable for reflection calling the parent class public method
*
* */
public static void main(String[] args) throws Exception {
    //1. Get
    //1.1. Get class object (equivalent to getting the whole watermelon)
    Class<?> clazz = Class.forName("com.czxy.demo2.Person");
    //1.2. Obtaining method through class object (equivalent to extracting watermelon pulp from watermelon through super ability)
    Method t1 = clazz.getMethod("t1");
    //1.3. Set available out of class (only for private, even if public is added, no error will be reported)
    t1.setAccessible(true);
    //2. Execution (equivalent to eating watermelon pulp)
    //2.1. Obtain the construction method through class object
    Constructor<?> c = clazz.getConstructor();
    //2.2. Create an object through the construction method (equivalent to Person person = new Person();)
    Object person = c.newInstance();
    //2.3. Call method (equivalent to person.t1())
    t1.invoke(person);
}

 

• getDeclaredMethod gets any method in the current class (ignoring the access modifier), which is suitable for reflection calling the current class method

• getMethod the current class or parent class obtains the public method, which is suitable for reflection calling the parent class public method

 

 

 

2, Advanced case 2: execute private field

Code implementation:
public static void main(String[] args) throws Exception {
    //1. Get
    //1.1. Get class object
    Class<?> clazz = Class.forName("com.czxy.demo2.Person");
    //1.2. Get fields through class objects
    Field name = clazz.getDeclaredField("name");
    //1.3. Set available out of class
    name.setAccessible(true);
    //2, implementation
    //2.1. Obtaining the construction method
    Constructor<?> c = clazz.getConstructor();
    //2.2 creating objects
    Object person = c.newInstance();
    //2.3. Call
    //assignment
    name.set(person,"Xiao Liu");
    //Value
    Object o = name.get(person);
    //Strong turn
    String str = (String) o;
    System.out.println(str);
}

 

 

 

3, Advanced case 3: execute public field

Code implementation:
public static void main(String[] args) throws Exception {
    //1. Get
    //1.1. Get class object
    Class<?> clazz = Class.forName("com.czxy.demo2.Person");
    //1.2. Get fields through class objects
    Field name = clazz.getField("n1");
    //1.3. Set available out of class (private only)
    //name.setAccessible(true);
    //2, implementation
    //2.1. Obtaining the construction method
    Constructor<?> c = clazz.getConstructor();
    //2.2 creating objects
    Object person = c.newInstance();
    //2.3. Call
    //Value
    Object o = name.get(person);
    //Strong turn
    String str = (String) o;
    System.out.println(str);
}

 

• getDeclaredField gets any field of the current class (regardless of the access modifier), which is suitable for getting the current class

• getField gets the public field in the current class and the parent class, which is applicable to getting the parent class public

 

 

 

4, Advanced 4: create objects through private construction method

/*
* Creating objects for a privatized constructor class by reflection
* */
public static void main(String[] args) throws Exception {
    //1. Get
    //1.1. Get class object
    Class<?> clazz = Class.forName("com.czxy.demo1.Person");
    //1.2. Obtain private nonparametric construction method through class object
    Constructor<?> c = clazz.getDeclaredConstructor();
    //1.3. Setting out of class availability (violent reflex)
    c.setAccessible(true);
    //2, implementation
    //2.1 creating objects
    Object obj = c.newInstance();
    //Strong turn
    Person person = (Person) obj;
}

 

 

 

Gets the object of the class of the privatized constructor, which depends on reflection.

 

 

5, Advanced 5: creating objects through the public construction method

/*
    * Creating objects by reflecting common classes
    *       getConstructor              Get any public constructor of the current class
    *       getDeclaredConstructor      Gets any constructor of the current class (regardless of the access modifier)
    * */
    public static void main(String[] args) throws Exception {
        //1. Get
        //1.1. Get class object
        Class<?> clazz = Class.forName("com.czxy.demo1.Phone");
        //1.2. Obtain private nonparametric construction method through class object
        Constructor<?> c = clazz.getConstructor();
        //1.3. Setting out of class availability (violent reflex)
//        c.setAccessible(true);
        //2, implementation
        //2.1 creating objects
        Object obj = c.newInstance();
        //Strong turn
        Phone person = (Phone) obj;
    }

 

• getConstructor gets any public constructor of the current class

• getDeclaredConstructor gets any constructor of the current class (regardless of the access modifier)

 

 

 

6, Advanced 6: create an object through the construction method with parameters

Preparation Code:

public class Phone {
    public Phone() {
        System.out.println("Public nonparametric construction-phone");
    }
    private Phone(String name,Integer age) {
        System.out.println("Private nonparametric construction-phone"+name+age);
    }
}

 

• Requirement Description:

Create the mobile phone object through the structure with parameters.

name: HUAWEI

age:100

 

• Code implementation:

/*
* Creating objects with a band parameter construct
* */
public static void main(String[] args) throws Exception {
    //1. Get
    //1.1. Get class object
    Class<?> clazz = Class.forName("com.czxy.demo1.Phone");
    //1.2. Get the construction method (String, Integer) through the class object
    Constructor<?> c = clazz.getDeclaredConstructor(String.class, Integer.class);
    //1.3. Setting out of class availability (violent reflex)
    c.setAccessible(true);
    //2, implementation
    //2.1. Create an object through the construction method
    Object phone = c.newInstance("HUAWEI", 100);
}

 

 

7, Reflection advanced 1-get all member methods & Field & construction methods

Requirement Description: get all methods & all fields & all construction methods in a class   getMethods(); get all public decorated methods in the current class and parent class getDeclaredMethods(); get all methods in the current class (regardless of access rights)   getFields(); get all public decorated fields in the current class and parent class getDeclaredFields(); gets all fields in the current class (regardless of the access modifier)   getConstructors(); get all the public decorated constructors in the current class getDeclaredConstructors(); get all construction methods in the current class (ignore access modifier)

Conclusion:

All methods without Declared can obtain all public contents of the current class and parent class

All methods with Declared can obtain all contents of the current class

 

 

8, Advanced 2: three ways to get class objects

/*
*   Three ways to get class objects
* */
public static void main(String[] args) throws Exception {
    //1. Class.forName
    Class<?> clazz1 = Class.forName("com.czxy.demo2.Person");
    //2. class name
    Class<Person> clazz2 = Person.class;
    //3. Object name. getClass() [get object]
    Person p = new Person();
    Class<? extends Person> clazz3 = p.getClass();

    //For the above three kinds of object acquisition methods, the acquired Class objects are all the same in heap memory
    System.out.println(clazz1==clazz2);
    System.out.println(clazz1==clazz3);
}

 

 

Today's summary:

Reflection: get member variables / member methods in a class specifically   Fixing steps: 1. Get 1.1. Get class object 1.2. Obtain content (member variable, member method) through class object 1.3. Setting out of class availability (violent reflex) 2, implementation 2.1. Obtain the construction method of the class through the class object 2.2. Create objects according to the construction method 2.3 calling content   Get member method / member variable / construction method: Unclaimed: public content in current class and parent class declared: any content of the current class (regardless of the access modifier)     getMethods() Class objects can be obtained in three ways: Class.forName("full class name"); class name.class Object name. getClass();

 

 

 

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