/*
# Map
Interface.
Major implementations include `HashMap` and `TreeMap`,
both of which inherit `AbstractMap`.
*Not* a collection:
http://stackoverflow.com/questions/2651819/why-doesnt-java-map-extends-collection
# TreeMap
Implements `Map`.
Javadoc says it's a red-black tree.
You can use a custom comparator to compare the entries without wrapping the key.
# HashMap
Implements `Map`.
You cannot use a custom hash function without wrapping the key:
http://stackoverflow.com/questions/5453226/java-need-a-hash-map-where-one-supplies-a-function-todo-the-hashing
# HashTable
Like `HashMap` but synchronized.
# EnumMap
Only for enum keys.
TODO why is it faster?
*/
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
public class MapCheat {
public static void main(String[] args) {
// Basic usage.
{
Map m = new TreeMap<>();
m.put(0, "zero");
m.put(1, "one");
assert m.get(0).equals("zero");
assert m.get(1).equals("one");
assert m.get(2) == null;
}
/*
# put
Returns the previous value for the key, null if none.
*/
{
Map m = new TreeMap<>();
assert m.put(0, 0) == null;
assert m.put(0, 1).equals(0);
assert m.put(0, 2).equals(1);
//assert(m.put(1, 1).equals(1));
}
/*
# entrySet
# Iterate over map
http://stackoverflow.com/questions/46898/iterate-over-each-entry-in-a-map
In Java 8, there is also the `forEach` loop version.
*/
{
//for (Map.Entry entry : map.entrySet()) {
//System.out.println(entry.getKey() + "/" + entry.getValue());
//}
/*
The entrySet is backed by the map. Modifications to it modify the map.
*/
{
Map m = new TreeMap<>();
assert m.put(1, -1) == null;
assert m.put(2, -2) == null;
Set entrySet = m.keySet();
Iterator it = entrySet.iterator();
while (it.hasNext())
if (it.next() == 1)
it.remove();
assert m.get(2) == -2;
assert m.size() == 1;
}
}
/*
# values
Collection of the values. Not a copy.
Not a set because there can be duplicates.
*/
/*
# keySet
Set of all the keys.
*/
}
}