JAVA expert please help me the program with hashCode() URL: https://en.wikipedia

Question

JAVA expert please help me the program with hashCode() URL: https://en.wikipedia.org/wiki/Java_hashCode()

import java.util.ArrayList;
import java.util.HashMap;

public class Register {

public static void main(String[] args) {
  HashMap<Section, ArrayList<String>> roster = new HashMap<>();
  Section s1 = new Section("CSC", 151, 0001, "Bob Charlotte", "Intro to Java");
  Section s2 = new Section("CSC", 151, 0001, "Bob C", "Introduction to Java");
  Section s3 = new Section("CSC", 151, 0001, "B Charlotte", "Java Introduction");
  Section s4 = new Section("CSC", 151, 0002, "Bob C", "Introduction to Java");
  Section s5 = new Section("DBA", 151, 0001, "Bob Charlotte", "SQL 1");
  Section s6 = new Section("CSC", 251, 0001, "Bob Charlotte", "Adv Java");
  
  registerAStudent(roster, s1, "bob");
  registerAStudent(roster, s2, "mike");
  registerAStudent(roster, s3, "peter");
  registerAStudent(roster, s4, "delco");
  registerAStudent(roster, s5, "tobias");
  registerAStudent(roster, s6, "adam");
  
  System.out.println(roster);
}

public static void registerAStudent(HashMap<Section, ArrayList<String>> roll, Section s, String student) {
  ArrayList<String> victims = roll.get(s);
  if (victims == null) {
   victims = new ArrayList<>();
   victims.add(student);
  }
  else {
   victims.add(student);
  }
  roll.put(s, victims);
}

}

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Explanation / Answer

Register.java

import java.util.ArrayList;
import java.util.HashMap;
public class Register {
public static void main(String[] args) {
HashMap<Section, ArrayList<String>> roster = new HashMap<Section, ArrayList<String>>();
Section s1 = new Section("CSC", 151, 0001, "Bob Charlotte", "Intro to Java");
Section s2 = new Section("CSC", 151, 0001, "Bob C", "Introduction to Java");
Section s3 = new Section("CSC", 151, 0001, "B Charlotte", "Java Introduction");
Section s4 = new Section("CSC", 151, 0002, "Bob C", "Introduction to Java");
Section s5 = new Section("DBA", 151, 0001, "Bob Charlotte", "SQL 1");
Section s6 = new Section("CSC", 251, 0001, "Bob Charlotte", "Adv Java");
  
registerAStudent(roster, s1, "bob");
registerAStudent(roster, s2, "mike");
registerAStudent(roster, s3, "peter");
registerAStudent(roster, s4, "delco");
registerAStudent(roster, s5, "tobias");
registerAStudent(roster, s6, "adam");
  
System.out.println(roster);
}

public static void registerAStudent(HashMap<Section, ArrayList<String>> roll, Section s, String student) {
ArrayList<String> victims = roll.get(s);
if (victims == null) {
victims = new ArrayList<String>();
victims.add(student);
}
else {
victims.add(student);
}
roll.put(s, victims);
}
}

Section.java

public class Section {
   private String department;
   private int courseNumber;
   private int sectorNumber;
   private String instructor;
   private String title;
   public Section(String d, int c, int s, String i, String t){
       department = d;
       courseNumber = c;
       sectorNumber = s;
       instructor = i;
       title = t;
   }
   public String getDepartment() {
       return department;
   }
   public void setDepartment(String department) {
       this.department = department;
   }
   public int getCourseNumber() {
       return courseNumber;
   }
   public void setCourseNumber(int courseNumber) {
       this.courseNumber = courseNumber;
   }
   public int getSectorNumber() {
       return sectorNumber;
   }
   public void setSectorNumber(int sectorNumber) {
       this.sectorNumber = sectorNumber;
   }
   public String getInstructor() {
       return instructor;
   }
   public void setInstructor(String instructor) {
       this.instructor = instructor;
   }
   public String getTitle() {
       return title;
   }
   public void setTitle(String title) {
       this.title = title;
   }
   @Override
public int hashCode() {
       final int PRIME = 31;
int result = 1;
result = PRIME * result + (department.length());
result = PRIME * result + (courseNumber);
result = PRIME * result + (sectorNumber);
result = PRIME * result + (title.length());
result = PRIME * result + (instructor.length());
result = PRIME * result + (department.length());
return result;
   }
}

Output:

{Section@42556246=[mike], Section@42552aef=[tobias], Section@425557bd=[peter], Section@425548f7=[bob], Section@47d66496=[adam], Section@4255d6a5=[delco]}

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