Things on this page are fragmentary and immature notes/thoughts of the author. Please read with your own judgement!

Plain Old Array

1. The length/size of array is as in the declaration. Each element of the array is initialized to the default value (null for object).

2. Array in Java does not have a size method, but it has a length member. This is because the length of an array won't change. Since String in Java is immutable, a string also has a length method instead of size method. But I think there inconsistent here, they should make String has a length member.

3. Array in Java is both static and dynatic while array is C/C++ is static. Because array is Java is actually object, so the memory is managed automatically. In C++, array is not object, if you want to make it dynamic, you must manage memory automatically.

4. You almost never need to use array is C++. You can use vector instead of array.

Class Collections

1. If you create a vector/list in C++ using the constructor taking a capacity parameter, the vector/list is fully initialized, i.e., every element of the vector/list is initialized. This is different from Java. If you create an ArrayList in Java using the constructor taking a capacity parameter, there's no element in the ArrayList, i.e., the ArrayList is empty, not to mention initialization of elements. The difference is because, an element of a vector/list in C++ is an object and it must have a valid value while an element of an ArrayList in in Java is a reference. A reference not necessarily has a valid value. Rather than initialize every element to be null, Java is lazy not to do anything.