3.6. HashMap

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Mon Sep 19 2022 03:54:11 GMT+0000 (Coordinated Universal Time)

package org.launchcode.java.demos.collections;

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class HashMapGradebook {

   public static void main(String[] args) {

      HashMap<String, Double> students = new HashMap<>();
      Scanner input = new Scanner(System.in);
      String newStudent;

      System.out.println("Enter your students (or ENTER to finish):");

      // Get student names and grades
      do {

         System.out.print("Student: ");
         newStudent = input.nextLine();

         if (!newStudent.equals("")) {
            System.out.print("Grade: ");
            Double newGrade = input.nextDouble();
            students.put(newStudent, newGrade);

            // Read in the newline before looping back
            input.nextLine();
         }

      } while(!newStudent.equals(""));

      // Print class roster
      System.out.println("\nClass roster:");
      double sum = 0.0;

      for (Map.Entry<String, Double> student : students.entrySet()) {
         System.out.println(student.getKey() + " (" + student.getValue() + ")");
         sum += student.getValue();
      }

      double avg = sum / students.size();
      System.out.println("Average grade: " + avg);
   }
}
//Notice how a HashMap called students is declared on line 11:
HashMap<String, Double> students = new HashMap<>();
//Here, <String, Double> defines the data types for this map’s <key, value> pairs. Like the ArrayList, when we call the HashMap constructor on the right side of the assignment, we don’t need to specify type.

//We can add a new item with a .put() method, specifying both key and value:
students.put(newStudent, newGrade);

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JAVA control flow and collections

@cruz

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3.6. HashMap

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