TreeMap class implements the java.util.SortedMap interface, which extends java.util.Map. : Map « Utility Classes « SCJP

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2. Utility Classes
3. Map

import java.util.Map;
import java.util.SortedMap;
import java.util.TreeMap;

public class MainClass {
  public static void main(String[] argv) {
    Map map = new TreeMap();
    map.put("key", "value");
    map.put("key2", "value2");
    map.put("key3", "value3");

    SortedMap sortedMap = (SortedMap) map;

  }
}