java-Tree-Map examples

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);
    }
}

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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);
    }
}

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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);

    }
}

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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);
    }
}