Loading process such as reflection

.java file compile （javac.exe） become .class file .class file Class loading （java.exe） Enter the method area of memory And use .class File contents create a Class object （ Class loading ） Next is , Class Links For example ： static int a=2; Link in class yes static int a=0; In class initialization, it becomes static int a=2; The three processes are sometimes collectively referred to as class loading

public static void main(String[] args) {
        // system class loader 
        ClassLoader classLoader = AnnoTest.class.getClassLoader();
        System.out.println(classLoader);//sun.misc.Launcher$AppClassLoader@18b4aac2
        // Extend the classloader 
        ClassLoader parent = classLoader.getParent();
        System.out.println(parent);//sun.misc.Launcher$ExtClassLoader@677327b6
        // Boot class loader 
        // Here is null It does not mean that there is no boot class loader , But can't get it , Can only jvm Self use 
        ClassLoader parent1 = parent.getParent();
        System.out.println(parent1);//null
    }

route ：

  @Test
    public  void t1() throws IOException {
        InputStream is = AnnoTest.class.getClassLoader().getResourceAsStream("b.properties");
        Properties properties = new Properties();
        properties.load(is);
        String user = properties.getProperty("user");
        System.out.println(user);

        FileInputStream fis = new FileInputStream("a.properties");
        Properties pro = new Properties();
        pro.load(fis);
        String user1 = pro.getProperty("user");
        System.out.println(user1);
    }

 @Test
    public void test2(){
        Class clazz = Person.class;
        Field[] declaredFields = clazz.getDeclaredFields();
        for(Field f : declaredFields){
            //1. Permission modifier 
            int modifier = f.getModifiers();
            System.out.print(Modifier.toString(modifier) + "\t");
            System.out.println("+++++++++++++++++++++++++++");
            //2. data type 
            Class type = f.getType();
            System.out.print(type.getName() + "\t");
            System.out.println("***************************");
            //3. Variable name 
            String fName = f.getName();
            System.out.print(fName);
        }
    }

public class MythodTest {

    /**
     * @Xxxx
     *  Permission modifier    return type    Method name ( Parameter type 1  The name of the parameter 1,...) throws XxxException{}
     */
    @Test
    public void test2() {
        Class clazz = Person.class;
        Method[] declaredMethods = clazz.getDeclaredMethods();
        for (Method m : declaredMethods) {
            //1. Get annotation for method declaration 
            Annotation[] annos = m.getAnnotations();
            for (Annotation a : annos) {
                System.out.println(a + "KKKK");
            }

            //2. Permission modifier 
            System.out.print(Modifier.toString(m.getModifiers()) + "\t");

            //3. return type 
            System.out.print(m.getReturnType().getName() + "\t");

            //4. Method name 
            System.out.print(m.getName());
            System.out.print("(");
            //5. Parameter list 
            Class[] pTs = m.getParameterTypes();
            if(!(pTs == null && pTs.length == 0)){
                for(int i = 0;i < pTs.length;i++){
                    if(i == pTs.length - 1){
                        System.out.print(pTs[i].getName() + " args_" + i);
                        break;
                    }
                    System.out.print(pTs[i].getName() + " args_" + i + ",");
                }
            }
            System.out.print(")");

            //6. Exception thrown 
            Class[] eTs = m.getExceptionTypes();
            if(eTs.length > 0){
                System.out.print("throws ");
                for(int i = 0;i < eTs.length;i++){
                    if(i == eTs.length - 1){
                        System.out.print(eTs[i].getName());
                        break;
                    }
                    System.out.print(eTs[i].getName() + ",");
                }
            }
            System.out.println("TQA");
        }
    }

Constructors

public class OtherTest {
    /**
     *  Get the structure of the constructor 
     */
    @Test
    public void test(){
        Class clazz = Person.class;
        //getConstructors(): Get the current class declaration in the runtime public Constructor 
        Constructor[] constructors = clazz.getConstructors();
        for(Constructor c : constructors){
            System.out.println(c);
        }
        System.out.println("************************");
        //getDeclaredConstructors(): Get all constructors declared in the current runtime class 
        Constructor[] declaredConstructors = clazz.getDeclaredConstructors();
        for(Constructor c : declaredConstructors){
            System.out.println(c);
        }
    }
}