"Integrity" - "firm adherence to a moral or artistic code" or "an unimpaired condition" or "the quality or state of being complete or undivided" are all definitions from the Merriam-Webster's Online Dictionary.
The implication of all these definitions is the person with integrity acts according to a well-thought out moral code or worldview, and their actions and words are consistent whether they are alone or in a group. Consistency of character under various circumstances, from times of peace and tranquility to instances of life-threatening stress, provides the evidence of integrity. Ones character and personality, developed from childhood, builds understanding of a personal worldview. Thoughtful self-discipline will help form your character even after the "formative years" have past. You may not be able to change your personality but you can change your actions. You decide how you will act, and why.
What you do and say, reflects who you are (how you think and feel), which dictates what you will become. If your worldview says people have value then what you do and say will provide the evidence of what you believe and show people you do value them. If what you believe, and how you act, shows you do not value certain people, or value some more than others, then your words and actions will provide all the evidence needed.
The foundation of integrity is one's moral code or worldview. Integrity is judged by others based upon the evidence of the consistency of your life. Integrity cannot be hidden. It depends upon the persons honesty with others, but especially with themselves. Someone who believes a lie, and bases their morality or worldview upon a lie, may still have unshakable integrity, but will be unable to convince many by their life of the truth of their worldview. The effects of believing a lie will become more and more apparent the older the person grows.
I think I need to end my ramble and invite discussion.
Gerald F. Ward