import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target(ElementType.CONSTRUCTOR) //约束条件。只能限定注解构造函数。
@Retention(value = RetentionPolicy.RUNTIME) //运行时。
public @interface Info {
    int id() default 0;
    String name() default "zhang";
    String password() default "123";
}

public class User {

    @Info(id = 1, name = "zhangphil", password = "123456")
    public User () {

    }
}

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;

import java.lang.reflect.Constructor;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        Constructor[] constructors = User.class.getConstructors();
        for (Constructor constructor : constructors) {
            if (constructor.isAnnotationPresent(Info.class)) {
                Info info = (Info) constructor.getAnnotation(Info.class);
                System.out.println(info.id());
                System.out.println(info.name());
                System.out.println(info.password());
            }
        }
    }
}

输出：