HashMaps upload

joeyajames · web-flow · commit e8193447da7b · 2023-04-26T08:45:10.000-07:00
diff --git a/MapFunctions.java b/MapFunctions.java
@@ -0,0 +1,71 @@
+// Java HashMap
+// Joe James 2023
+
+import java.util.Map;
+import java.util.HashMap;
+import java.util.Map.Entry;
+import java.util.stream.*;
+
+class MapFunctions {
+	public static void main (String[] args) {
+		// 1. Create a HashMap, add kv pairs
+		Map<String, Integer> ages = new HashMap<String, Integer>();
+		// OR, to initialize capaacity,
+		// Map<String, Integer> ages = new HashMap<String, Integer>(100);
+		ages.put("Avni",11);
+		ages.put("Bing", 12);
+		ages.put("Cassie", 13);
+		ages.put("Devarshi", 14);
+		System.out.println(ages);
+
+		// 2. Get an item from the map
+		String person = "Cassie";
+		System.out.println(person + " : " + ages.get(person));
+		System.out.println("Frank" + " : " + ages.getOrDefault("Frank", 0));
+
+		// 3. Check for membership
+		System.out.println("Contains key Avni?: " + ages.containsKey("Avni"));
+		System.out.println("Contains value 23?: " + ages.containsValue(23));
+
+		// 4. Remove an item from the map
+		ages.remove("Bing");
+		System.out.println(ages);
+		ages.remove("Devarshi", 41);
+		System.out.println(ages);
+
+		// 5. Get count of items in map
+		System.out.println("Num Items = " + ages.size());
+
+		// 6. Remove all items from map
+		ages.clear();
+		System.out.println("Empty map? " + ages.isEmpty());
+		ages.put("Elena", 15);
+		ages.put("Frank", 16);
+		System.out.println(ages);
+
+		// 7. Conditional add & replace
+		ages.putIfAbsent("George", 23); 
+		ages.putIfAbsent("Elena", 5);
+		System.out.println(ages);
+		ages.replace("George", 23, 17);
+		ages.replace("George", 44, 55);
+		System.out.println(ages);
+
+		// 8. Get collection of Values
+		System.out.println(ages.values());
+
+		// 9. Iterate keys using enhanced for loop
+		for (String key : ages.keySet()) {
+			System.out.println(key +  " : " + ages.get(key));
+		}
+
+		// 10. Iterate KV pairs using enhanced for loop
+		for (Map.Entry<String, Integer> pair : ages.entrySet()) {
+			System.out.println(pair.getKey() + " : " + pair.getValue());
+		}
+
+		// 11. Iterate KV pairs using Java 8 Stream API
+		ages.entrySet().stream().forEach(pair ->  System.out.println(pair.getKey() + " : " + pair.getValue()));
+
+	}
+}
