HashMap resizing its table

Question

I understand that the size of the HashMap is 16 by default and we also can provide some other value to it .What if i have initialized the size as 5 with a load factor of 0.8f and then i add the fifth element to it.Does it grow to 10 or 16?Does it jumps to power of two once the threshold breach happens for a non power of 2 value?

Answer 1

It is always best to have a look at the source code:

 final Node<K,V>[]  [More ...] resize() {      
         Node<K,V>[] oldTab = table;  
         int oldCap = (oldTab == null) ? 0 : oldTab.length;
         int oldThr = threshold;
         int newCap, newThr = 0;   
         if (oldCap > 0) {   
             if (oldCap >= MAXIMUM_CAPACITY) {   
                 threshold = Integer.MAX_VALUE;   
                 return oldTab;    
             }    
             else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&   
                      oldCap >= DEFAULT_INITIAL_CAPACITY)    
                 newThr = oldThr << 1; // double threshold    
         }    
         else if (oldThr > 0) // initial capacity was placed in threshold    
             newCap = oldThr;
         ...
         // The capacity of the inner data structure is doubled
         Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];
         table = newTab;
         ...

So, the current capacity and threshold are doubled upon resize.

However, constructing a HashMap object with initial capacity that is not a power of 2 is not possible! Constructor converts the initial capacity into the power of 2:

static final int tableSizeFor(int cap) {
     int n = cap - 1;
     n |= n >>> 1;
     n |= n >>> 2;
     n |= n >>> 4;
     n |= n >>> 8;
     n |= n >>> 16;
     return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY: n + 1;
 }

public  [More ...] HashMap(int initialCapacity, float loadFactor) {
     ...
     this.loadFactor = loadFactor;
     this.threshold = tableSizeFor(initialCapacity);
}