| MapUser.java |
package lectures.arrays.collections_kinds;
import util.annotations.WebDocuments;
import java.util.HashMap;
import java.util.Map;
import bus.uigen.ObjectEditor;
/**
* MAPS/TABLES
*
* A Map (Table) is probably the most important structured type in Java - some languages
* have just primitive types and tables.
*
* Take a look at the program and run it.
*
* Then uncomment the last three statements and run the program again.
*
* (T/F) The get(k) operation on a Map instance returns k, if a previous
* operation on the instance was put(k, v).
*
* (T/F) The get(k) operation on a Map instance returns v, if a previous
* operation on the instance was was put(k, v), and this was the most recent
* put that used k.
*
* (T/F) The get(k) operation on a Map instance returns null if some put(k,v)
* was not previously executed on the instance.
*
* (T/F) The get(k) operation on a Map instance throws an exception if some put(k,v)
* was not previously executed on the instance.
*
* (T/F) Executing put (k, null) on a Map instance results in a runtime error.
*
* (T/F) It is possible to execute put(k, v) on a Map instance if a put (k, v2)
* was previously executed on it.
*
*
*/
@WebDocuments({"Lectures/ArraysCollectionsKinds.pptx", "Lectures/ArraysCollectionsKinds.pdf", "Videos/ArraysCollectionsKinds.avi"})
public class MapUser {
public static void main (String[] args) {
Map aMap = new HashMap();
aMap.put("Nadal", 14);
aMap.put("Federer", 17);
aMap.put("Djokovic", 11); // There is a later "put" for this name. What does the first put mean?
System.out.println(aMap.get("Djokovic"));
System.out.println(aMap.get("djokovic")); // Does case matter?
aMap.put("Djokovic", 12); // What does a subsequent put mean?
System.out.println(aMap.get("Djokovic"));
System.out.println(aMap);
/*
* Uncomment the following statements
*/
// aMap.put ("me", null);
// System.out.println (aMap.get("me"));
// System.out.println (aMap);
}
}
/*
* Next class: JavaCollectionHierarchy
*/