How do I create a hash table in Java?

import java.util.HashMap;

Map map = new HashMap();

Also don't forget that both Map and Hashtable are generic in Java 5 and up (as in any other class in the Collections framework).

Map<String, Integer> numbers = new HashMap<String, Integer>();
numbers.put("one", 1);
numbers.put("two", 2);
numbers.put("three", 3);

Integer one = numbers.get("one");
Assert.assertEquals(1, one);

You can use double-braces to set up the data. You still call add, or put, but it's less ugly:

private static final Hashtable<String,Integer> MYHASH = new Hashtable<String,Integer>() {{
    put("foo",      1);
    put("bar",      256);
    put("data",     3);
    put("moredata", 27);
    put("hello",    32);
    put("world",    65536);
 }};

Map map = new HashMap();
Hashtable ht = new Hashtable();

Both classes can be found from the java.util package. The difference between the 2 is explained in the following jGuru FAQ entry.