Help Fix Errors please and Thank you!

Program errors displayed here

CourseGradebook.java:$38$: error: cannot find symbol

public ArrayList getSortedAssignmentNames$()\{$

$^$

symbol: class ArrayList

location: class CourseGradebook

CourseGradebook.java:$48$: error: cannot find symbol

public ArrayList getSortedStudentIDs$()\{$

$^$

symbol: class ArrayList

location: class CourseGradebook

CourseGradebook.java:$3$: error: CourseGradebook is not abstract and does not override abstract method getStudentScores$($Integer$)$ in Gradebook

public class CourseGradebook extends Gradebook $\{$

$^$

CourseGradebook.java:$30$: error: cannot find symbol

for $($GradebookEntry entry : gradebookEntries$)\{$

$^$

symbol: variable gradebookEntries

location: class CourseGradebook

CourseGradebook.java:$30$: error: cannot find symbol

for $($GradebookEntry entry : gradebookEntries$)\{$

$^$

symbol: class GradebookEntry

location: class CourseGradebook

CourseGradebook.java:$39$: error: cannot find symbol

HashSet assignmentNamesSet $=$ new HashSet;

$^$

symbol: class HashSet

location: class CourseGradebook

CourseGradebook.java:$39$: error: cannot find symbol

HashSet assignmentNamesSet $=$ new HashSet;

$^$

symbol: class HashSet

location: class CourseGradebook

CourseGradebook.java:$40$: error: cannot find symbol

for $($GradebookEntry entry : gradebookEntries$)\{$

$^$

symbol: variable gradebookEntries

location: class CourseGradebook

CourseGradebook.java:$40$: error: cannot find symbol

for $($GradebookEntry entry : gradebookEntries$)\{$

$^$

symbol: class GradebookEntry

location: class CourseGradebook

CourseGradebook.java:$43$: error: cannot find symbol

ArrayList sortedAssignmentNames $=$ new ArrayListassignmentNamesSet$)$;

$^$

symbol: class ArrayList

location: class CourseGradebook

CourseGradebook.java:$43$: error: cannot find symbol

ArrayList sortedAssignmentNames $=$ new ArrayListassignmentNamesSet$)$;

$^$

symbol: class ArrayList

location: class CourseGradebook

CourseGradebook.java:$44$: error: cannot find symbol

Collections.sort$($sortedAssignmentNames$)$;

$^$

symbol: variable Collections

location: class CourseGradebook

CourseGradebook.java:$49$: error: cannot find symbol

HashSet studentIDsSet $=$ new HashSet;

$^$

symbol: class HashSet

location: class CourseGradebook

CourseGradebook.java:$49$: error: cannot find symbol

HashSet studentIDsSet $=$ new HashSet;

$^$

symbol: class HashSet

location: class CourseGradebook

CourseGradebook.java:$50$: error: cannot find symbol

for $($GradebookEntry entry : gradebookEntries$)\{$

$^$

symbol: variable gradebookEntries

location: class CourseGradebook

CourseGradebook.java:$50$: error: cannot find symbol

for $($GradebookEntry entry : gradebookEntries$)\{$

$^$

symbol: class GradebookEntry

location: class CourseGradebook

CourseGradebook.java:$53$: error: cannot find symbol

ArrayList sortedStudentIDs $=$ new ArrayListstudentIDsSet$)$;

$^$

symbol: class ArrayList

location: class CourseGradebook

CourseGradebook.java:$53$: error: cannot find symbol

ArrayList sortedStudentIDs $=$ new ArrayListstudentIDsSet$)$;

$^$

symbol: class ArrayList

location: class CourseGradebook

CourseGradebook.java:$54$: error: cannot find symbol

Collections.sort$($sortedStudentIDs$)$;

$^$

symbol: variable Collections

location: class CourseGradebook

CourseGradebook.java:$61$: error: cannot find symbol

for $($GradebookEntry entry : gradebookEntries$)\{$

$^$

symbol: variable gradebookEntries

location: class CourseGradebook

CourseGradebook.java:$61$: error: cannot find symbol

for $($GradebookEntry entry : gradebookEntries$)\{$

$^$

symbol: class GradebookEntry

location: class CourseGradebook

$21$ errors