Why ignoring type safety warnings is bad

ListsAreNotCovariant.java

List<Foo> specialThings = Lists.newArrayList(); //Foo extends Base

Bean bean = new Bean();
// normally you would correctly get a compile error here, 
//but the setter in your example does an unsafe cast that makes this line compile
bean.setStuff(specialThings); 

List<Base> things = bean.getStuff();
things.add(new Bar()); // Bar extends Base

//compiles fine, but explodes at runtime as the first element in the list is a Bar, not a Foo
Foo boom = specialThings.get(0);