How can I initialize an ArrayList with all zeroes in Java

Question

It looks like arraylist is not doing its job for presizing      presizing   ArrayList lt Integer gt  list   new ArrayList lt Integer gt  60     Afterwards when I try to access it   list get 5     Instead of returning 0 it throws IndexOutOfBoundsException  Index 5 out of bounds for length 0   Is there a way to initialize all elements to 0 of an exact size like what C   does

User · Answer

The 60 you re passing is just the initial capacity for internal storage  It s a hint on how big you think it might be  yet of course it s not limited by that  If you need to preset values you ll have to set them yourself  e g    for  int i   0  i  lt  60  i          list add 0

User · Answer

apparently this is broken  Whoops for me  java util Collections fill list new Integer 0        this is better Integer   data   new Integer 60   Arrays fill data new Integer 0    List lt Integer gt  list   Arrays asList data

User · Answer

The integer passed to the constructor represents its initial capacity  i e   the number of elements it can hold before it needs to resize its internal array  and has nothing to do with the initial number of elements in the list    To initialize an list with 60 zeros you do   List lt Integer gt  list   new ArrayList lt Integer gt  Collections nCopies 60  0        If you want to create a list with 60 different objects  you could use the Stream API with a Supplier as follows   List lt Person gt  persons   Stream generate Person  new                                limit 60                                collect Collectors toList

User · Answer

It s not like that  ArrayList just uses array as internal respentation  If you add more then 60 elements then underlaying array will be exapanded  How ever you can add as much elements to this array as much RAM you have

User · Answer

Java 8 implementation  List initialized with 60 zeroes    List lt Integer gt  list   IntStream of new int 60                        boxed                        collect Collectors toList        new int N  - creates an array filled with zeroes  amp  length N  boxed   - each element boxed to an Integer collect Collectors toList    - collects elements of stream

[java] How can I initialize an ArrayList with all zeroes in Java?

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