Create java-Tree-Map examples

java-Tree-Map examples

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+import java.util.Map;
+import java.util.TreeMap;
+
+public class AccessEntriesFromTreeMapExample {
+    public static void main(String[] args) {
+        TreeMap<Integer, String> employees = new TreeMap<>();
+
+        employees.put(1003, "Rajeev");
+        employees.put(1001, "James");
+        employees.put(1002, "Sachin");
+        employees.put(1004, "Chris");
+
+        System.out.println("Employees map : " + employees);
+
+        // Finding the size of a TreeMap
+        System.out.println("Total number of employees : " + employees.size());
+
+        // Check if a given key exists in a TreeMap
+        Integer id = 1004;
+        if(employees.containsKey(id)) {
+            // Get the value associated with a given key in a TreeMap
+            String name = employees.get(id);
+            System.out.println("Employee with id " + id + " : " + name);
+        } else {
+            System.out.println("Employee does not exist with id : " + id);
+        }
+
+        // Find the first and last entry
+        System.out.println("First entry in employees map : " + employees.firstEntry());
+        System.out.println("Last entry in employees map : " + employees.lastEntry());
+
+        // Find the entry whose key is just less than the given key
+        Map.Entry<Integer, String> employeeJustBelow = employees.lowerEntry(1002);
+        System.out.println("Employee just below id 1002 : " + employeeJustBelow);
+
+        // Find the entry whose key is just higher than the given key
+        Map.Entry<Integer, String> employeeJustAbove = employees.higherEntry(1002);
+        System.out.println("Employee just above id 1002 : " + employeeJustAbove);
+    }
+}
+
+***********************************************************************************************************************************************************************
+
+import java.util.Comparator;
+import java.util.SortedMap;
+import java.util.TreeMap;
+
+public class CreateTreeMapCaseInsensitiveOrderExample {
+    public static void main(String[] args) {
+        // TreeMap with keys sorted by ignoring case
+        SortedMap<String, String> fileExtensions = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
+
+        /*
+            The above statement is the short form of -
+            SortedMap<String, String> fileExtensions = new TreeMap<>(new Comparator<String>() {
+                @Override
+                public int compare(String s1, String s2) {
+                    return s1.compareToIgnoreCase(s2);
+                }
+            });
+        */
+
+        fileExtensions.put("PYTHON", ".py");
+        fileExtensions.put("c++", ".cpp");
+        fileExtensions.put("KOTLIN", ".kt");
+        fileExtensions.put("Golang", ".go");
+
+        // The keys will be sorted ignoring the case (Try removing String.CASE_INSENSITIVE_ORDER and see the output)
+        System.out.println(fileExtensions);
+    }
+}
+
+***********************************************************************************************************************************************************************
+
+import java.util.Comparator;
+import java.util.SortedMap;
+import java.util.TreeMap;
+
+public class CreateTreeMapCustomComparatorExample {
+    public static void main(String[] args) {
+        // Creating a TreeMap with a Custom comparator (Descending order)
+        SortedMap<String, String> fileExtensions = new TreeMap<>(new Comparator<String>() {
+            @Override
+            public int compare(String s1, String s2) {
+                return s2.compareTo(s1);
+            }
+        });
+
+        /*
+            The above TreeMap with custom Comparator can be simply written as -
+            SortedMap<String, String> fileExtensions = new TreeMap<>(Comparator.reverseOrder());
+        */
+
+        // Adding new key-value pairs to a TreeMap
+        fileExtensions.put("python", ".py");
+        fileExtensions.put("c++", ".cpp");
+        fileExtensions.put("kotlin", ".kt");
+        fileExtensions.put("golang", ".go");
+        fileExtensions.put("java", ".java");
+
+        // Printing the TreeMap (The keys will be sorted based on the supplied comparator)
+        System.out.println(fileExtensions);
+
+    }
+}
+
+***********************************************************************************************************************************************************************
+
+import java.util.Map;
+import java.util.TreeMap;
+
+public class RemoveEntriesFromTreeMapExample {
+    public static void main(String[] args) {
+        TreeMap<String, String> countryISOCodeMapping = new TreeMap<>();
+
+        countryISOCodeMapping.put("India", "IN");
+        countryISOCodeMapping.put("United States of America", "US");
+        countryISOCodeMapping.put("China", "CN");
+        countryISOCodeMapping.put("United Kingdom", "UK");
+        countryISOCodeMapping.put("Russia", "RU");
+        countryISOCodeMapping.put("Japan", "JP");
+
+        System.out.println("CountryISOCodeMapping : " + countryISOCodeMapping);
+
+        // Remove the mapping for a given key
+        String countryName = "Japan";
+        String isoCode = countryISOCodeMapping.remove(countryName);
+        if(isoCode != null) {
+            System.out.println("Removed (" + countryName + " => " + isoCode + ") from the TreeMap. New TreeMap " + countryISOCodeMapping);
+        } else {
+            System.out.println(countryName + " does not exist, or it is mapped to a null value");
+        }
+
+        // Remove the mapping for the given key only if it is mapped to the given value
+        countryName = "India";
+        boolean isRemoved = countryISOCodeMapping.remove(countryName, "IA");
+        System.out.println("Was the mapping removed for " + countryName + "? : " + isRemoved);
+
+        // Remove the first entry from the TreeMap
+        Map.Entry<String, String> firstEntry = countryISOCodeMapping.pollFirstEntry();
+        System.out.println("Removed firstEntry : " + firstEntry + ", New TreeMap : " + countryISOCodeMapping);
+
+        // Remove the last entry from the TreeMap
+        Map.Entry<String, String> lastEntry = countryISOCodeMapping.pollLastEntry();
+        System.out.println("Removed lastEntry : " + lastEntry + ", New TreeMap : " + countryISOCodeMapping);
+    }
+}