Memory overhead of Java HashMap compared to ArrayList

Question

I am wondering what is the memory overhead of java HashMap compared to ArrayList?

Update:

I would like to improve the speed for searching fo

Answer 1

HashMap hold a reference to the value and a reference to the key.

ArrayList just hold a reference to the value.

So, assuming that the key uses the same memory of the value, HashMap uses 50% more memory ( although strictly speaking , is not the HashMap who uses that memory because it just keep a reference to it )

In the other hand HashMap provides constant-time performance for the basic operations (get and put) So, although it may use more memory, getting an element may be much faster using a HashMap than a ArrayList.

So, the next thing you should do is not to care about who uses more memory but what are they good for.

Using the correct data structure for your program saves more CPU/memory than how the library is implemented underneath.

EDIT

After Grant Welch answer I decided to measure for 2,000,000 integers.

Here's the source code

This is the output

$
$javac MemoryUsage.java  
Note: MemoryUsage.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
$java -Xms128m -Xmx128m MemoryUsage 
Using ArrayListMemoryUsage@8558d2 size: 0
Total memory: 133.234.688
Initial free: 132.718.608
  Final free: 77.965.488

Used: 54.753.120
Memory Used 41.364.824
ArrayListMemoryUsage@8558d2 size: 2000000
$
$java -Xms128m -Xmx128m MemoryUsage H
Using HashMapMemoryUsage@8558d2 size: 0
Total memory: 133.234.688
Initial free: 124.329.984
  Final free: 4.109.600

Used: 120.220.384
Memory Used 129.108.608
HashMapMemoryUsage@8558d2 size: 2000000