Private class members in reflected class

Here:
http://docs.oracle.com/javase/tutorial/reflect/index.html
is a discussion of reflection. One part says:
Exposure of Internals
    Since reflection allows code to perform operations that would be illegal in non-reflective code, such as accessing private fields and methods, the use of reflection can result in unexpected side-effects, which may render code dysfunctional and may destroy portability. Reflective code breaks abstractions and therefore may change behavior with upgrades of the platform.

How and why does this happen? Why do class members lose their access modifier definition?
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allelopathAsked:
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ramazanyichCommented:
IT is due to setAccessible API which is available in reflection APi.
lets say you have class:
public class PrivateObject {

  private String privateString = null;

  public PrivateObject(String privateString) {
    this.privateString = privateString;
  }
}

by usin reflection API you can get privateString value

Field privateStringField = PrivateObject.class.
            getDeclaredField("privateString");

privateStringField.setAccessible(true);

String fieldValue = (String) privateStringField.get(privateObject);
System.out.println("fieldValue = " + fieldValue);

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ramazanyichCommented:
same setAccesible API is applicable for Method
Sharon SethCommented:
Reflective code breaks abstractions

Say the following is a property in your class and you have a setter for this property:

private List  items;

public void setItems(Map items)
{
   this.items = items;
}      

Here you have declared an abstraction over the underlying collection for items . The actual collection used can be any of the List implementations

When you go for reflection and try to access the setter on items , but items was assigned  an ArrayList , then the reflection mechanism would throw  NoSuchMethodException , clearly breaking the abstraction you had defined .
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