HashMap<String, Student> searching for instance in Student class - search

Question

I am working with two helper classes (Student, Helper), as well as a main class.
In the Student class, I have the following constructor:
Student(String iName, String iMajor, int iNumber) {
name = iName;
major = iMajor;
number = iNumber;
}
In the Helper class, I declare a HashMap as follows:
HashMap<String, Student> students = new HashMap<String, Student>();
Now, I have written a few method for adding (put) new students into the HashMap construction, as well as a method for retrieving information about a student based on the name.
//Adding new students
Student s1 = new Student("Alex", "Biology", 19);
Student s2 = new Student("Brian", "Chemistry", 20);
Student s3 = new Student("Tom", "Biology", 20);
//etc...
//Get student from name (key)
public Student getFromKey(String key) {
return students.get(key);
}
I am now looking to write a method that finds all students based on either major or number. For instance, the call:
helper.getStudents("Biology");
Should return all the students studying Biology. I imagine the method looking something like:
public Student getStudents(String searchItem) {
for(Students st : students.values()) {
if(searchItem.equals(??)) {
return st;
//Something like this.
However, I can't seem to figure out how to access these values. All the classes have appropriate getter and setter methods, and the program works fine. Any help is highly appreciated!

Answer 1

Assuming this Map exists:
HashMap<String, Student> students = new HashMap<String, Student>();
The following would work:
public Student getStudents(String searchItem) {
for(Map.Entry<String,Student> entry : students.entrySet()) {
Student student = entry.getValue();
//perform conditional logic here
}
Here is a more complete example in case you need it:
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
public class Student {
private String name;
private String major;
private int number;
public Student(String name, String major, int number) {
super();
this.name = name;
this.major = major;
this.number = number;
}
public static void main(String[] args) {
List<String> names = Arrays.asList("Joe", "Jack", "John","James");
List<String> majors = Arrays.asList("English","Math","Geography");
Map<String,Student> students = new HashMap<String,Student>();
for(int i = 0; i < 100; i++){
Collections.shuffle(names);
Collections.shuffle(majors);
students.put(names.get(0) + String.valueOf(i), new Student(names.get(0), majors.get(0), i));
}
List<Student> mathMajors = getStudents(students, "Math");
for(Student student:mathMajors){
System.out.println(student.name);
System.out.println(student.major);
}
}
public static List<Student> getStudents(Map<String,Student> students, String searchToken){
List<Student> results = new ArrayList<Student>();
for(Entry<String,Student> entry:students.entrySet()){
if(entry.getValue().getMajor().equalsIgnoreCase(searchToken)){
results.add(entry.getValue());
}
}
return results;
}
public String getName() {
return this.name;
}
public void setName(String name) {
this.name = name;
}
public String getMajor() {
return this.major;
}
public void setMajor(String major) {
this.major = major;
}
public int getNumber() {
return this.number;
}
public void setNumber(int number) {
this.number = number;
}
}
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