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


  5.  

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