Core Java Programming Question from Collection

1. Program to find the frequency string in string array (Passing String from command line arguments)
   
   package com.myconceptsonjava.practice;
   
   import java.util.ArrayList;
   import java.util.HashMap;
   import java.util.List;
   import java.util.Map;
   
   public class Test {
      
   public static void main(String[] args) {
       Map<String, Integer> m = new HashMap<String, Integer>();
   
       // Initialize frequency table from command line
       for (String a : args) {
       Integer freq = m.get(a);
       m.put(a, (freq == null) ? 1 : freq + 1);
       }
       System.out.println(m);
   }
   }
2. Program to find the frequency string in string array and print them in natural  sorting order (Passing String from command line arguments)package com.myconceptsonjava.practice;
   
   import java.util.ArrayList;
   import java.util.TreeMap;
   import java.util.List;
   import java.util.Map;
   
   public class Test {
      
   public static void main(String[] args) {
       Map<String, Integer> m = new TreeMap<String, Integer>();
   
       // Initialize frequency table from command line
       for (String a : args) {
       Integer freq = m.get(a);
       m.put(a, (freq == null) ? 1 : freq + 1);
       }
       System.out.println(m);
   }
   }
3.  Program to delete duplicate record of of custom object from list using set .
   package com.myconceptsonjava.practice;
   public class Person {
   
       Integer id;
       String name;
       String dept;
       public Person(int id,String name,String dept) {
       this.id=id;
       this.name=name;
       this.dept=dept;
       }
       public int getId() {
           return id;
       }
       public void setId(int id) {
           this.id = id;
       }
       public String getName() {
           return name;
       }
       public void setName(String name) {
           this.name = name;
       }
       public String getDept() {
           return dept;
       }
       public void setDept(String dept) {
           this.dept = dept;
       }
   
       @Override
       public boolean equals(Object obj) {
            if(obj instanceof Person)
               {
                Person temp = (Person) obj;
                   return this.name.equals(temp.name) && this.dept.equals(temp.dept) ;// && this.description == temp.description)
                     
               }
               return false;
       }
      
       @Override
       public int hashCode() {
           return 1;
   }}
   
   package com.myconceptsonjava.practice;
   import java.util.ArrayList;
   import java.util.HashSet;
   import java.util.Iterator;
   import java.util.List;
   
   public class RemoveDuplicateTest {
   
       public static void main(String[] args) {
           Person p1 = new Person(1, "A", "d1");
           Person p2 = new Person(2, "B", "d1");
           Person p3 = new Person(1, "A", "d1");
           Person p4 = new Person(4, "C", "d2");
           Person p5 = new Person(5, "D", "d2");
   
           List<Person> listPerson = new ArrayList<Person>();
           listPerson.add(p5);
           listPerson.add(p4);
           listPerson.add(p3);
           listPerson.add(p2);
           listPerson.add(p1);
   
           HashSet hs = new HashSet();
           hs.addAll(listPerson);
   
           Iterator<Person> itr = hs.iterator();
           while (itr.hasNext()) {
               Person p = itr.next();
               System.out.println(p.getName() + " " + p.getDept());
           }
       }
   }
   
   Output:-
   D d2
   C d2
   A d1
   B d1
   Note :ouput order sequence will varry because of HashSet