How do you convert an ArrayList to a HashMap?

Answer 1

Unfortunately, there seems to be no built in way of adding all elements of a list to a map. This means that we need to iterate through each element of the ArrayList and add it to the HashMap individually.

/**
* Generic method to add all elements from source into dest.
*/
public static final void addAll(final ArrayList source, final HashMap dest) {

// Iterate through each element in source and put it in dest.
for (int i = 0; i < source.size(); ++i) {

// We will use the index of each element of source as the key in dest.
dest.put(i, source.get(i));

}

}

Sample use:

// Create a new ArrayList and add some stuff to it.
ArrayList list = new ArrayList();
list.add(1); list.add(2); list.add(3);
list.add(4); list.add(5); list.add(6);
list.add(7); list.add(8); list.add(9);

// Print out our list
System.out.println(list);

// Create a new map and call our function
HashMap map = new HashMap();
addAll(list, map);

// Print out to verify identical contents
System.out.println(map);