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ArrayList is generic, so if you do not define the objects put in, you must do so when you take them out. Solution 1 is to cast the object when you get it from the list

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Please post the code and errors you are receiving, both of which are a wealth of information to help solve your problem

ArrayList colors = new ArrayList();
//add all colors to the list
for ( int i = 0; i < colors.size(); i++ ){
myPen.setColor(colors.get(i));
}