PropertyUtils java

PropertyUtils is written using java reflection api and provides you ability to modify properties of Java object at runtime.

In the link
 http://javarevisited.blogspot.com/2012/04/java-propertyutils-example-getting-and.html
it was mentioned as below

Remember we don’t know anything about Object on compile time. On runtime Object is provided to program along with name of property to retrieve or modify:

Read more: http://javarevisited.blogspot.com/2012/04/java-propertyutils-example-getting-and.html#ixzz2uX3g47Zr

Why we do not know anything about object at compile time but  runtime Object is provided to program along with name of property to retrieve or modify.

I am not clear on those statements.
I ran above program in the javarevisited link, I got output as below
PropertyUtils Example property value: blue

what is the meaning of output

I see we are setting and getting colr from PropertyUtils
   

  //here color and blue strings can come from variety or sources
        //e.g. configuration files, database, any upstream system or via HTTP Request
        PropertyUtils.setProperty(flexiColor, "color", "blue");
        String value = (String) PropertyUtils.getProperty(flexiColor, "color");
        System.out.println("PropertyUtils Example property value: " + value);

How is it different from regular getter and setter from a bean.

 PropertyUtils.setProperty(flexiColor, "color", "blue");

Where is this setter defined.

please advise

I see code as below

    PropertyUtils.getPropertyDescriptor(obj, fieldName).getWriteMethod().invoke(obj, list);

What is the meaning of above code while parsing a text document which has not only primitives but also list kind of objects before sending to one other system.
please advise

How the reflection on class, method, field are different.
Any practical example to understand this reflection concept end to end better with set up on eclipse. please advise