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We're taught that Java's ArrayList is less efficient for integers, because the list actually contains pointers, while an array of ints contains the integers in place, thus avoiding memory allocations and access.
My question is whether the JDK/JIT compiler optimizes this kind of inefficiency away? It has all the information to conclude these implementations are functionally equivalent , so it might as well replace ArrayList with an int[]-backed implementation under the hood.
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ArrayList can not be used for primitive types, like int, char, etc.
An array can be converted to an ArrayList using the following methods: Using ArrayList. add() method to manually add the array elements in the ArrayList: This method involves creating a new ArrayList and adding all of the elements of the given array to the newly created ArrayList using add() method.
Java ArrayList class can contain duplicate elements. Java ArrayList class maintains insertion order. Java ArrayList class is non synchronized. Java ArrayList allows random access because the array works on an index basis.
ArrayList<Integer> numbers = new ArrayList<>(Arrays. asList(1, 2, 3, 4, 5, 6)); This is how you declare an ArrayList of Integer values. You can do the same to create an ArrayList with String objects as well, e.g.
No, it can't, because you can store null in an ArrayList.
EDIT: Oh, and it also can't because generics are erased at compile time — at run time, the JRE can't distinguish ArrayLists by their element types. IOW, it's worse than just null — you can store any object in an ArrayList<Integer>.
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