Shoot, I might as well jump into this.
In Judaism charity is given voluntarily, in that the person with the money does decides to give it, and how much between 10-20% of his income, and when, and to whom they should give it. We have no worldly offices that do our accounting; telling us how much to give. No being on earth decides that we should give more or less.
That said, it is still a commandment. A G-d given law that we practice justice. G-d wills to the cent how much each person has, and how much will come into their hands. The justice involved is when you realize the poor exist for the rich to give charity to, because that is the reason the rich have their wealth. The purpose of the 10% every person must give is that they realize that money comes from the hands of G-d for the purpose of giving out.
And, this is not communism, because as it is written in the communist manefesto wealth will be redistributed after a violent revolution ( I am heavily rephrasing) which is in effect theft. So, as opposed to communism which purports itself to being just, Judaism recognizes there are legitimate reasons each person has whay he owns, so that the Vanderbilts, and the Rockefellers of the world did rightly get their money, as it came from G-d. Therefore stealing would prevert the natural order.