Well an array list is like an array except it's endless. An array can ONLY hold a limited amount of items you tell it to whereas an array list can hold as many items and constantly grows to hold more items. With that said, you can get stuff from (for example): for (int I = 0; I < arraylist.size(); I++) { if (arraylist.get(i).getId() == 1) { sysout("found!"); } } when you say arraylist.get(i), it's an Employee object- meaning it has all the employee methods (accessors/mutators aka getters/setters). Using an enhanced for each loop is the same thing except no need to say arraylist.get(i) anymore since emp is the same as arraylist.get(i) More on reddit.com

Java has something called autoboxing and unboxing . Integer is an object. int is a primitive type. An Integer object can be unboxed into a int. And an int can be autoboxed into a Integer. In the examples above the List contains Integer objects. The difference is: In the first, val is a reference to the Integer object in the List. In the second, val is a primitive value that was unboxed from the Integer object in the List. More on reddit.com

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why isn't every List a Stream? To answer this part of the question, it's because a stream is a fundamentally different datatype than a list. A list represents a collection of data, while a stream represents a pipeline for processing data. Streams can only be processed once, and are designed to perform multiple operations on some provided data. They don't store any intermediate results, and then do lazy processing once you specify a terminal operator (like toList() or forEach()). For example, if you had something like this: Stream a = List.of(1, 2, 3).stream(); Stream b = a.filter(n -> n > 1); Stream c = b.map(n -> String.valueOf(n)); List d = c.toList(); This is functionally identical to this: List d = List.of(1, 2, 3).stream() .filter(n -> n > 1) .map(n -> String.valueOf(n)) .toList(); If you inspected b, however, it would not contain any data about what elements were remaining, because the stream has not executed yet. Assigning the various steps of the stream along the way doesn't actually DO anything to the data, it just creates pointers to instances of the pipeline. As mentioned before, the pipeline can only be executed once, which means a stream is consumed when you perform a terminal operation on it. It also can't be executed if you chain it to another pipeline. If, in the example above, you tried to do b.toList(), you'd get an IllegalStateException, because b was already operated on. If you did c.toList(), you'd get a list of "2", "3". If you did c.toList() a second time, you'd once again get an IllegalStateExcecution, because c has already been consumed. The intermediate operators like map actually do nothing except modify the pipeline definition until you call toList at the end. Once you execute toList, then the pipeline operates in a lazy way, evaluating the data elements one at a time. So, to recap: List: collection of ordered data Stream: an operation pipeline definition More on reddit.com