Student Records with and without Maps

StudentRecords.java

package org.wecancodeit.objects.maps;

import java.util.ArrayList;
import java.util.List;

import org.wecancodeit.objects.students.Student;

public class StudentRecords {

	public static void main(String[] args) {

		List<Student> students = new ArrayList<>(); // same as
													// ArrayList<Student>();

		Student harvey = new Student("23A52", "Harvey Dent");
		students.add(harvey);

		students.add(new Student("68Z29", "Jessica Jones"));

		Student jj = new Student("57W85", "J Jonah Jameson");
		students.add(jj);
		
		System.out.println(jj);
		System.out.println(students);
		
		String lookingFor = "Harvey Dent";
		for(Student current: students) {
			System.out.println("Current: " + current);
			// same as if(current.name.equalsIgnoreCase(lookingFor)) {
			if(lookingFor.equalsIgnoreCase(current.name)) {
				System.out.println("Found my student. His id is " + current.id);
				break;
			}
		}
	}
}

StudentRecordsWithMap.java

package org.wecancodeit.objects.maps;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

public class StudentRecordsWithMap {

	public static void main(String[] args) {
//		Student harvey = new Student("23A52", "Harvey Dent");
//		Student jessica = new Student("68Z29", "Jessica Jones");
//		Student jj = new Student("57W85", "J Jonah Jameson");
		
		Map<String, String> students = new HashMap<String, String>();
		
		students.put("68Z29", "Jessica Jones");
		System.out.println("hashcode for 68Z29 is " + "68Z29".hashCode());
		System.out.println(students);

		students.put("23A52", "Harvey Dent");
		System.out.println("hashcode for 23A52 is " + "23A52".hashCode());
		System.out.println(students);
		
		String studentName = students.get("23A52");
		System.out.println("I found student " + studentName);
		
		// common map methods
		
		// collection views
		System.out.println("Student names (map values) are " + students.values());
		System.out.println("Student ids (map keys) are " + students.keySet());
		// use entrySet() when you need both key and value
		System.out.println("Student entries (key/value pairs) are " + students.entrySet());
		
		System.out.println("Iterating over student names:");
		for(String currentName: students.values()) {
			System.out.println(currentName);
		}
		
		System.out.println("Iterating over entries:");
		for(Entry<String, String> entry: students.entrySet()) {
			String key = entry.getKey(); // student id
			String value = entry.getValue(); // student name
			System.out.println("key is " + key + ", value is " + value);
		}
		
		// sorting a list (sidebar)
		System.out.println("Sorting a list:");
		List<String> listOfClasses = new ArrayList<String>();
		listOfClasses.add("Philosophy");
		listOfClasses.add("Creative Writing");
		System.out.println(listOfClasses);
		Collections.sort(listOfClasses);
		System.out.println(listOfClasses);
		
		// is this a valid student id?
		if(students.containsKey("23A52")) { //Harvey Dent's id
			System.out.println("Yes, 23A52 is a valid student id");
		}
		if(students.containsKey("1234")) { // bad one
			System.out.println("Found the key"); // doesn't print
		}
		
		// is this a valid student name?
		if(students.containsValue("Harvey Dent")) {
			System.out.println("Found Harvey!");
		}
		
		// do we have any students?
		if(!students.isEmpty()) {
			System.out.println("We have students!");
		}
		
		// sorry, Harvey. You're DC
		students.remove("23A52"); // his id is the key
		System.out.println(students);
		
		// how many students are there?
		System.out.println("There are " + students.size() + " students.");
	}
}