Reflection - class object function - get method (case)

Get the object's 3 Ways of planting ：

1.Class.forNane(" Full class name ")： Load the bytecode file into memory , return Class object

apply ： More for configuration files , Define the class name in the configuration file . Read the file , Load class

2. Class name .class: Through the properties of the class name class obtain

apply ： It is mainly used for parameter passing

3. object .getClass():getClass() Method in Object It defines

apply ： It is mainly used for obtaining bytecode of objects

summary ： The same bytecode file （*.class） In a program run , It will only be loaded once , Either way class The objects are all the same .

Case study ：

* demand ： Write a framework , You can't change any code of this class , Can help us create objects of any class , And execute any of these methods

* Realization ：

1. The configuration file

2. Reflection

* step ：

1. Define the full class name of the object to be created and the method to be executed in the configuration file

2. Load the read configuration file in the program

3. Use reflection technology to load class files into memory

4. Create objects

5. Execution method

Example ：

First create three classes ：student.java ;Person.java And a main method ReflectTest class

They are as follows ：

public class Student {
    public void sleep(){
        System.out.println("sleep...");
    }
}

public class Person {
    private String name;
    private int age;

    public Person() {
    }

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

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

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
    public void eat(){
        System.out.println("eat...");
    }
}

public class ReflectTest {
    public static void main(String[] args) throws Exception {
        // You can create objects of any kind , Any method can be executed 
        /*
        *  Premise ： You can't change any code for this class , You can create objects of any kind , Any method can be executed 
        * */
      /*  Person p=new Person();
        p.eat();*/
        //1. Load the file 
        //1.1 establish Properties object 
        Properties p=new Properties();
        //1.2 Load profile , Convert to a collection 
        //1.2.1 obtain class The configuration file under the directory 
        ClassLoader cls = ReflectTest.class.getClassLoader();
        InputStream is = cls.getResourceAsStream("pro.properties");
        p.load(is);
        //2. Get the data defined in the configuration file 
        String className = p.getProperty("className");
        String methodName = p.getProperty("methodName");
        //3. Load this class into memory 
        Class aClass = Class.forName(className);
        //4. Create objects 
        Object obj = aClass.newInstance();
       //5. Get object method 
        Method method = aClass.getMethod(methodName);
        //6. Execution method 
        method.invoke(obj);
    }
}

The second step is src in new File Name a new file :pro.proterties

className=cn.itcast.junit.domain.Student
methodName=sleep

The third step ： function ReflectTest class , give the result as follows

sleep...