Comparable Generics TreeMap

Author: gil-son

Collection/Map/src/ex06/.gitignore

@@ -0,0 +1,5 @@
+/ComparableTreeMap.class
+/ComparableTreeMap$1.class
+/Main.class
+/ComparableGenericsTreeMap$1.class
+/ComparableGenericsTreeMap.class

Collection/Map/src/ex06/ComparableGenericsTreeMap.java

@@ -0,0 +1,64 @@
+package ex06;
+
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.SortedSet;
+import java.util.TreeSet;
+
+// https://stackoverflow.com/questions/2864840/treemap-sort-by-value
+
+public class ComparableGenericsTreeMap {
+
+	static <K,V extends Comparable<? super V>> SortedSet<Map.Entry<K,V>> entriesSortedByValues(Map<K,V> map) {
+		
+        SortedSet<Map.Entry<K,V>> sortedEntries = new TreeSet<Map.Entry<K,V>>( new Comparator<Map.Entry<K,V>>() {
+        	
+                @Override public int compare(Map.Entry<K,V> e1, Map.Entry<K,V> e2) {
+                    int res = e1.getValue().compareTo(e2.getValue());
+                    return res != 0 ? res : 1; // Special fix to preserve items with equal values
+                }
+            }
+        );
+        
+        sortedEntries.addAll(map.entrySet());
+        return sortedEntries;
+    }
+
+}
+
+
+
+class Main {
+
+	public static void main(String[] args) {
+
+		// now with Integer
+		
+		Map<String, Integer> nonSortedMap = new HashMap<String, Integer>();
+		nonSortedMap.put("ape", 1);
+		nonSortedMap.put("pig", 3);
+		nonSortedMap.put("cow", 1);
+		nonSortedMap.put("frog", 2);
+		
+		ComparableGenericsTreeMap comparableTreeMap = new ComparableGenericsTreeMap();
+		
+		
+		System.out.println(comparableTreeMap.entriesSortedByValues(nonSortedMap));
+		
+		// now with String
+		
+		Map<String, String> nonSortedMap2 = new HashMap<String, String>();
+		nonSortedMap2.put("ape", "a");
+		nonSortedMap2.put("pig", "x");
+		nonSortedMap2.put("cow", "v");
+		nonSortedMap2.put("frog", "a");
+		
+		ComparableGenericsTreeMap comparableTreeMap2 = new ComparableGenericsTreeMap();
+		
+		
+		System.out.println(comparableTreeMap2.entriesSortedByValues(nonSortedMap2));
+		
+	}
+
+}