New to Java

I'm confused about the need to case when using the getKey()/getValue() when using Map.

Here's the example that I wrote for Student class.

public class Student
{
	int studentID;
	String name;
	double mark;
	
	Student(int id, String n, double m)
	{
		studentID = id;
		name = n;
		mark = m;
	}
	
	public int getID()
	{
		return studentID;
	}
	
	public String getName()
	{
		return name;
	}
	
	public double getMark()
	{
		return mark;
	}
}

import java.util.*;

public class StudentTest
{
	public static void main(String[] args)
	{
		Student s1 = new Student(123, "Jane", 60.5);
		Student s2 = new Student(456, "John", 76.5);
		Student s3 = new Student(789, "Jim", 85);
		
		int[] studentID = new int[3];
		double[] mark = new double[3];
		
		Map<Integer, Student> students = new HashMap<Integer, Student>();
		
		students.put(s1.getID(), s1);
		students.put(s2.getID(), s2);
		students.put(s3.getID(), s3);
		
		int i=0, index = 0;
		for (Map.Entry<Integer, Student> entry: students.entrySet())
		{
			index = i++;
			studentID[index] = entry.getKey();
			mark[index] = entry.getValue().getMark();			
		}
		
		for (int num=0; num<mark.length; num++)
		{
			System.out.println("ID: " +studentID[num]);
			System.out.println("Mark: " +mark[num]);			
		}		
	}
}

My confusion lies in understanding the API. The getKey() returns K object. This K refers to Integer and V to Student assuming if I'm right.
1) Does this mean that I need to cast this line?

studentID[index] = entry.getKey();

to->

 studentID[index] = (Integer)entry.getKey().intValue(); 

2)As the Value is a Student object. If I were to retrieve any of student variables, eg mark, I don't need to type cast it? ie double mark when entered into HashMap isn't converted to Double(obj). It still remains a double(prim). Is my understanding correct?

Thanks.