This is the 20th day of my participation in the November Gwen Challenge. Check out the details: The last Gwen Challenge 2021

package reflecttest;

public class Person {
	public int age;
	private String name;
	
	public Person(a) {
		// TODO automatically generated constructor stubs
	}
	
	public Person(String name) {
		super(a);this.name = name;
	}
	
	private Person(String name,int age) {
		super(a);this.name = name;
		this.age = age;
	}

	public int getAge(a) {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	public String getName(a) {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public void show(String name,int age) {
		System.out.println("Deja, turn.");
	}
    
   private void fly(a) {
		System.out.println("Deja, fly.");
	}
    
   private String Work(String name,int age) {
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Three ways to get an instance of Class

An instance of Class is a runtime Class

  1. Class via the Class literal constant class.class

    		Class clazz = Person.class;
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  2. Return an instance of Class type through the getClass() method of the Object Class

    		Person person = new Person();
		Class clazz = person.getClass();
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  3. Obtain the Class object corresponding to the Class name using the static method class.forname (” full Class name “)

    		Class clazz = Class.forName("reflecttest.Person");
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Create objects through reflection

There are two main ways to create Class objects by reflection, through the newInstance() method of a Class object and through the newInstance() method of a Constructor object.

  1. The first is through newInstance() on Class objects.

    		// Get an instance of the Class object
		Class clazz = Person.class;

		// Create Person object
		Person person = (Person)clazz.newInstance();
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  2. Second: newInstance() via the Constructor object

    		// Get an instance of the Class object
		Class clazz = Person.class;

		// Create Person object
		Constructor constructor = clazz.getConstructor();
		Person person = (Person)constructor.newInstance();
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Class objects created from a Constructor object can select a specific Constructor, whereas only the default no-argument Constructor can be used from a Class object.

Example :(calling the parameter constructor to initialize a class object)

		// Get an instance of the Class object
		Class clazz = Person.class;
		
		// Create Person object
		Constructor constructor = clazz.getConstructor();
		Person person = (Person) constructor.newInstance("Tiga".16);
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Invoke object properties through reflection

Retrieve attributes

Two ways to get all the attributes

  1. getFields()

    		// Use getFields() to get the person.class and all public-decorated attributes in the parent class
		Field[] fields = clazz.getFields();
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  2. getDeclaredFields()

    		GetDeclaredFields () to get all the attributes in person.class
		Field[] fields = clazz.getDeclaredFields();	
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Note:

GetFields () retrieves all public attributes of this class and its parent. GetDeclaredFields () retrieves all attributes of this class. Include public, private, protected, and default-modified attributes, excluding those in the parent class

Two ways to get a specified property

  1. getField(String name)

    		// Get the age property in person.class with getField()
		Field field = clazz.getField("age");
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  2. getDeclaredField(String name)

    		GetDeclaredField () to get the name attribute in person.class
		Field field = clazz.getDeclaredField("name");	
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Note:

GetField (String name) getDeclaredField(String name) getDeclaredField(String name) getDeclaredField(String name) Include public, private, protected, and default-modified attributes, excluding those in the parent class

Operations on properties

Setting property values

		GetDeclaredField () to get the name attribute in person.class
		Field field = clazz.getDeclaredField("name");

		// If the property is private, access permissions need to be set to assign the value
		field.setAccessible(true);

		// Set (Object obj, Object value) to "dija"
		field.set(person, "Tiga");
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Note: If the property is private, you need to set setAccessible(true) to assign the value

Get property values

		// Get the Field property of the Person Object through get(Object obj)
		String name = (String) field.get(person);
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Gets the type of the property

		GetType () to get the type of the attribute
		Class type = field.getType();

		// Get the type name of the attribute
		String typename = field.getType().getName();
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Get attribute name

		// Call getName() to get the property name
		String fieldname = field.getName();
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Get the modifier type

		// Call getModifiers() to get modifier types,
		int modifier = field.getModifiers();

		ToString (int mod) change to public, private, protected, default
		String modifiername = Modifier.toString(modifier);
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Note :0-default, 1-public, 2-private, 4-protected

The sample

		// Get an instance of the Class object
		Class clazz = Person.class;
		
		// Create Person object
		Person person = (Person) clazz.newInstance();
		
		GetDeclaredField () to get the name attribute in person.class
		Field field = clazz.getDeclaredField("age");	
		field.setAccessible(true);
		// Set the age property of the person object to "12" through set()
		field.set(person, 12);	
		
		// Get the modifier
		int modifier = field.getModifiers();
		String modifiername = Modifier.toString(modifier);
		// Get the attribute type name
		String typename = field.getType().getName();
		// Get the attribute name
		String fieldname = field.getName();
		// Get the attribute value
		int fieldvalue = field.getInt(person);

		System.out.println(modifiername+""+typename+""+fieldname+"="+fieldvalue+";");
		
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Public int age = 12;

Call object methods through reflection

Access method

Two ways to get all the methods

  1. getMethods()

    		// Use getMethods() to get all the public modifier methods in the Person class and its parent
		Method[] methods =clazz.getMethods();
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  2. getDeclaredMethods()

    		GetDeclaredMethods () to get all the methods in the Person class
		Method[] methods = clazz.getDeclaredMethods();
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Note:

GetMethods () retrieves all public methods of this class and its parent. GetDeclaredMethods () retrieves all methods of this class. Methods that include public, private, protected, and default modifications, excluding methods in parent classes

Two ways to take the specified method

The method name and parameter list are used to determine the method to get

  1. getMethod(String name, class<? >... parameterTypes)

    		// Get the show method from the Person class with the method name, the list of parameters for show()
		Method method =clazz.getMethod("show",String.class,int.class);
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  2. GetDeclaredMethod (String name, class <? >... parameterTypes)

    		// Get the fly method from the Person class with the method name and the fly() invisible parameter list
		Method method = clazz.getDeclaredMethod("fly");
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Note:

GetMethod () gets the public modifier of this class and its parent. GetDeclaredMethod () gets the public modifier of this class. Include public, private, protected, and default-modified attributes, excluding those in the parent class

Operations on methods

A method is called

		// Get the fly method from the Person class with the method name and the fly() invisible parameter list
		Method method = clazz.getDeclaredMethod("fly");

		// If the method is private, you need to set the access permission
		method.setAccessible(true);

		// Call the fly method in person
		method.invoke(person);
		// If the method is static, the following method can be used: the current class calls the method
		//method.invoke(Person.class);
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Note: The return value of the invoke() method is the same as that of the called method

Gets the parameter list for the method

		// Get the parameter list
		Class[] paramTypes =method.getParameterTypes();	
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Get method name

		// Get the method name
		String methodname = method.getName();
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Gets the modifier type of the method

		// Get the method modifier
		int modifier = method.getModifiers();
		String modifiername = Modifier.toString(modifier);
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Gets the return value type of the method

		// Get the return value typeClass<? > returntype =method.getReturnType();// Get the name of the return value type
		String returntypename = returntype.getName();
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The sample

	public static void main(String[] args) throws Exception, IllegalAccessException {
		// Get an instance of the Class object
		Class clazz = Person.class;
		
		// Create Person object
		Person person = (Person) clazz.newInstance();
		
		// Get the method in the Person class
		Method method = clazz.getDeclaredMethod("Work",String.class,int.class);
		
		// Set permissions
		method.setAccessible(true);
		
		// Get the method name
		String methodname = method.getName();
		
		// Get the method modifier
		int modifier = method.getModifiers();
		String modifiername = Modifier.toString(modifier);
		
		// Get the return value typeClass<? > returntype =method.getReturnType();// Get the name of the return value type
		String returntypename = returntype.getName();
		
		// Get the parameter list
		Class[] paramTypes =method.getParameterTypes();	
		
		System.out.print(modifiername+""+returntypename+""+methodname+"(");
		
		// Prints method parameters
		printParamTypes(paramTypes);
			
	}
    /** * Print method arguments *@param paramTypes
     */
    private static void printParamTypes(Class[] paramTypes) {
        for (int j = 0; j < paramTypes.length; ++j) {
            if (j > 0) {
                System.out.print(",");
            }
            System.out.print(paramTypes[j].getName());
        }
        System.out.println(");");
    }
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Private java.lang.String Work(java.lang.String,int);

Call the object constructor through reflection

Get constructor

Two ways to get all constructors

  1. getConstructors()

    		// Get all public modifier constructors, excluding the parent class
		Constructor[] constructors = clazz.getConstructors();
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  2. getDeclaredConstructors()

    		// Get all constructors, including public, private, protected, default, excluding the parent class
		Constructor[] constructors = getDeclaredConstructors();
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Note:

GetConstructors () can get in this class all public the structure of the modified method, not including the superclass getgetDeclaredConstructors () can get all this class constructor. Methods that include public, private, protected, and default modifications, excluding parent classes

Gets two ways to specify a constructor

The choice of constructor depends on the type of parameter list

  1. clazz.getConstructor()

    		// Get a parameterless constructor
		Constructor constructor = clazz.getConstructor();
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  2. getDeclaredConstructor()

    		// Get a constructor that takes (String,int)
		Constructor constructor = clazz.getDeclaredConstructor(String.class,int.class);
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Note:

GetConstructor () gets only the public constructor of this class, excluding the parent getDeclaredConstructor(). Methods that include public, private, protected, and default modifications, excluding parent classes

Operations on constructors

Create an object

The choice of constructor depends on the type of parameter list

		// Get the constructor for the empty parameter
		//Constructor constructor = clazz.getDeclaredConstructor();
		Constructor constructor = clazz.getDeclaredConstructor(String.class,int.class);
	
		// If the constructor is private, set permissions
		constructor.setAccessible(true);
		
		// Create person object
		Person person = (Person)constructor.newInstance("Tiga".20);
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Gets the constructor’s argument list

		// Get the constructor parameter list
		Class[] paramTypes = constructor.getParameterTypes();
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Gets the constructor name

		// Get the constructor name
		String constructorname = constructor.getName();
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Gets the modifier type of the constructor

		// Get the constructor modifier
		int modifier = constructor.getModifiers();
		String modifiername = Modifier.toString(modifier);
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The sample

public static void main(String[] args) throws Exception, IllegalAccessException {
		// Get an instance of the Class object
		Class clazz = Person.class;

		// Get the constructor with parameters
		Constructor constructor = clazz.getDeclaredConstructor(String.class,int.class);
	
		// If the constructor is private, set permissions
		constructor.setAccessible(true);
		
		// Create person object
		Person person = (Person)constructor.newInstance("Tiga".20);
		
		// Get the constructor name
		String constructorname = constructor.getName();
		
		// Get the constructor modifier
		int modifier = constructor.getModifiers();
		String modifiername = Modifier.toString(modifier);
		
		// Get the constructor parameter list
		Class[] paramTypes = constructor.getParameterTypes();
		
		System.out.print(modifiername+""+constructorname+"(");
		
		// Prints method parameters
		printParamTypes(paramTypes);
		
	}
    /** * Print method arguments *@param paramTypes
     */
    private static void printParamTypes(Class[] paramTypes) {
        for (int j = 0; j < paramTypes.length; ++j) {
            if (j > 0) {
                System.out.print(",");
            }
            System.out.print(paramTypes[j].getName());
        }
        System.out.println(");");
    }
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Private test1.person (java.lang.string,int);