Reflection based on Java

How to create a class object? There are two ways:
class.forName("class name");
Class a = a.class;
The difference between the two is: forName() will help you initialize the static variables; while Class a = a.class needs to initialize static variables by itself; reflection, dynamic proxy; through reflection, you can implement the method of obtaining class; that is, the method of object; use a newInstace; it can be changed from class to an object; nstanceof can determine a certain Whether a class belongs to another class is used to determine when downward transformation;

Through the class object, you can obtain: the constructor, member variables, member methods, and access members of a certain class;

Get the constructors:
class.getConstructors(); Get the public constructors;
class.getDeclaredConstructors(); Get all the constructors;
class. getConstructor(null); Get the public, no-parameter constructor;
These methods return a Constructor con; the class object of the constructor; the object can be created through con.newInstance("parameter passing") ;

Get member variables:
class.getFields(); Get all public fields;
class.getDeclaredFields(); Get all fields;
class.getField("name"); Get a certain public specific field (name);
class.getDeclaredField("phoneNum"); Get a certain private field phoneNum;
Return Field; Use set to set it Our member variables; f.set(obj, "Andy Lau"); among them, our obj is an object generated by our class;

Getting member method:
class.getMethods(); Get all public methods;
class.getDeclaredMethods(); Get all methods;
class.getMethod("Method name", String.class); Get a single specific method ; The following String.class refers to our method parameter;
returns a Method object; then what we have to do is just like a Field, first generate an object; m.invoke(obj,20); In this we use the method execution function invoke(), obj is the object, and 20 is the parameter;
can even directly reflect our main() method; class.getMethod("main", Stirng[].class); Through reflection, we can implement it on the original basis, read Properties to implement reflection, create new classes, and execute methods; use reflection to avoid generic checks: we can even call the class file of a certain container, and then Call his method to avoid the problem of generic checking;

In addition, we can also implement the dynamic proxy mode through reflection:

interface Subject{
    public void doSomething();
}
class RealSubject implements Subject{
    public void doSomething(){
        System.out.println("call doSomething()");    
    }
}
class ProxyHandler implements InvocationHandler{
    private Object tar;
    public Object bind(Object tar){
       this.tar = tar;
       return Proxy.newProxyInstance(tar.getClass().getClassLoader(),
                                      tar.getClass().getInterfaces(),
                                      this);
     }
     public Object invoke(Object proxy, Method method ,Object[] args) throws Throwable{
         Object result = null;
        result = method.invoke(tar,args);
        return result;
    }
}
public class Test
{
    public static void main(String[] args[]){
        ProxyHandler proxy = new ProxyHandler();
        Subject sub = (Subject) proxy.bind(new RealSubject());
        sub.doSomething();
    }
}

A ProxyHandler is used to implement From the InvocationHandler interface, a proxy object is obtained by passing in a real object. The required parameters are: tar.getClass().getClassLoader() the class loader of the real object, tar.getClass().getInterfaces() the real object The interface, as well as this and the InvocationHandler itself, obtain a proxy object through the reflection mechanism, and at the same time write our real object in the method execution function of this proxy object for execution. In order to call the method of our real object first in subsequent method calls; remember to convert the object down to the real object when calling the bind of the proxy object.

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