How to sort keys in TreeMap by using Comparator with user define objects?

Problem statement:
How to sort keys in TreeMap by using Comparator with user defined objects.

1. import java.util.Comparator;
2. import java.util.Set;
3. import java.util.TreeMap;
4. public class SortByKeyUserDefine {
5.     public static void main(String a[]) {
6.         //By using name comparator (String comparison)
7.         System.out.println("========= Sort by name ==============");
8.         TreeMap<Employee, String> tm = new TreeMap<Employee, String>(new MyNameComp());
9.         tm.put(new Employee("Ram", 3000), "RAM");
10.         tm.put(new Employee("John", 6000), "JOHN");
11.         tm.put(new Employee("Crish", 2000), "CRISH");
12.         tm.put(new Employee("Tom", 2400), "TOM");
13.         Set<Employee> keys = tm.keySet();
14.         for (Employee key : keys) {
15.             System.out.println(key + " ==> " + tm.get(key));
16.         }
17.         System.out.println("========= Sort by salary ==============");
18.         //By using salary comparator (int comparison)
19.         TreeMap<Employee, String> trmap = new TreeMap<Employee, String>(new MySalaryComp());
20.         trmap.put(new Employee("Ram", 3000), "RAM");
21.         trmap.put(new Employee("John", 6000), "JOHN");
22.         trmap.put(new Employee("Crish", 2000), "CRISH");
23.         trmap.put(new Employee("Tom", 2400), "TOM");
24.         Set<Employee> ks = trmap.keySet();
25.         for (Employee key : ks) {
26.             System.out.println(key + " ==> " + trmap.get(key));
27.         }
28.     }
29. }
30. 
    
31. class MyNameComp implements Comparator<Employee> {
32.     @Override
33.     public int compare(Employee e1, Employee e2) {
34.         return e1.getName().compareTo(e2.getName());
35.     }
36. }
37. 
    
38. class MySalaryComp implements Comparator<Employee> {
39.     @Override
40.     public int compare(Employee e1, Employee e2) {
41.         if (e1.getSalary() > e2.getSalary()) {
42.             return 1;
43.         } else {
44.             return -1;
45.         }
46.     }
47. }
48. 
    
49. class Employee {
50.     private String name;
51.     private int salary;
52.     public Employee(String n, int s) {
53.         this.name = n;
54.         this.salary = s;
55.     }
56.     public String getName() {
57.         return name;
58.     }
59.     public void setName(String name) {
60.         this.name = name;
61.     }
62.     public int getSalary() {
63.         return salary;
64.     }
65.     public void setSalary(int salary) {
66.         this.salary = salary;
67.     }
68.     public String toString() {
69.         return "Name: " + this.name + " , Salary: " + this.salary;
70.     }
71. }

Output:

========= Sort by name ==============

Name: Crish , Salary: 2000 ==> CRISH

Name: John , Salary: 6000 ==> JOHN

Name: Ram , Salary: 3000 ==> RAM

Name: Tom , Salary: 2400 ==> TOM

========= Sort by salary ==============

Name: Crish , Salary: 2000 ==> null

Name: Tom , Salary: 2400 ==> null

Name: Ram , Salary: 3000 ==> null

Name: John , Salary: 6000 ==> null

How do you sort alphanumeric key of a map OR Sort map by key in java?

Problem statement:
How do you sort alphanumeric key of a map ?

1. import java.util.HashMap;
2. import java.util.Map;
3. import java.util.Set;
4. import java.util.TreeMap;
5. public class SortAlphanumericKeyInMap {
6.     public static void main(String[] args) {
7.         Map<String, String> map = new HashMap<>();
8.         map.put("A1BB", "1");
9.         map.put("A2CC", "2");
10.         map.put("A2AA", "2");
11.         map.put("B1AA", "7");
12.         Map<String, String> treeMap = new TreeMap<>(map);
13.         Set<String> keys = treeMap.keySet();
14.         for (String key : keys) {
15.             System.out.println(key);
16.         }
17.     }
18. }

Output:

A1BB

A2AA

A2CC

B1AA

How do you sort alphanumeric key of a map OR Sort map by key in java?

Problem statement:
How do you sort alphanumeric key of a map ?
Method-I:

1. import java.util.HashMap;
2. import java.util.Map;
3. import java.util.Set;
4. import java.util.TreeMap;
5. public class SortAlphanumericKeyInMap {
6.     public static void main(String[] args) {
7.         Map<String, String> map = new HashMap<>();
8.         map.put("question1", "1");
9.         map.put("question9", "2");
10.         map.put("question4", "2");
11.         map.put("question6", "7");
12.         // using TreeMap
13.         Map<String, String> treeMap = new TreeMap<>(map);
14.         Set<String> keys = treeMap.keySet();
15.         for (String key : keys) {
16.             System.out.println(key);
17.         }
18.     }
19. }

Output:

question1

question4

question6

question9

Method-II:

import java.util.*;

public class SortAlphanumericKeyInMap {

    public static void main(String[] args) {

        Map<String, String> map = new HashMap<>();

        map.put("question1", "1");

        map.put("question9", "2");

        map.put("question4", "2");

        map.put("question6", "7");

        Set<String> set = map.keySet();
        // This will iterate across the map in natural order of the keys.

        SortedSet<String> keys = new TreeSet<>(set);

        for (String key : keys) {

            System.out.println("sorted key: " + key + " | values: " + map.get(key));

        }

    }

}

Output:

sorted key: question1 | values: 1

sorted key: question4 | values: 2

sorted key: question6 | values: 7

sorted key: question9 | values: 2

Method-III:

import java.util.ArrayList;

import java.util.HashMap;

import java.util.Map;

import java.util.Set;

import java.util.List;

import java.util.Collections;

public class SortAlphanumericKeyInMap {

    public static void main(String[] args) {

        Map<String, String> map = new HashMap<>();

        map.put("question1", "1");

        map.put("question9", "2");

        map.put("question4", "2");

        map.put("question6", "7");

        Set set = map.keySet();

        // using List

        List keys = new ArrayList(set);

        Collections.sort(keys);

        for (Object key : keys) {

            System.out.println(key);

        }

    }

}

Output:

question1

question4

question6

question9