Please look at the TODO part and help me with this following code

package fp;

import java.math.BigDecimal;

import java.util.ArrayList;

import java.util.Comparator;

import java.util.Map;

import java.util.function.$*$;

import java.util.List;

class ExerciseNotCompletedException extends RuntimeException $\{$

public ExerciseNotCompletedException$()\{$

super$("$Exercise is not completed yet"$)$;

$\}$

$\}$

$/**$

$*\{$@link HW$\}$ is an exercise class. Each method returns a functional interface and it should be implemented

$*$ using either lambda or a method reference. Every method that is not implemented yet throws

$*\{$@link ExerciseNotCompletedException$\}.$

$*$

$*$ TODO: remove exception and implement each method of this class using lambda or method reference

$*$

$*$ TODO: to get the most out of your learning, visit our website

$*$

$*$

$*/$

record pair $($U u$,$ V v$)\{\}$

public class HW $\{$

$//$ precondition: l$1$ and l$2$ have the same length

static List$>$ zip$($List l$1,$ List l$2)\{$

$//$ walk through the U$\text{'}$s and V$\text{'}$s

$//$ construct list of pairs

ArrayList$>$ l $=$ new ArrayList$<>()$;

for $($int i $=0$; i $<$ l$1.$size$()$; i$++)\{$

l$.$add$($new pair$($l$1.$get$($i$),$l$2.$get$($i$)))$;

$\}$

return l;

$//$ ArrayList l $=$ new ArrayList$<>()$;

$//$ for $($int i $=0$; i $<$ l$1.$size$()$; i$++)\{$ l$.$add$($i$)$; $\}$

$//$ return map$($l$,$ i $->$ new pair$<>($l$1.$get$($i$),$ l$2.$get$($i$)))$;

$\}$

$//$ postcondition: result has the same length as l

static List map$($List l$,$ Function f$)\{$

$//$ walk through the U$\text{'}$s

$//$ use f at every stage f$.$apply

$//$ construct list of V$\text{'}$s

ArrayList l$2=$ new ArrayList$<>()$;

for $($U x: l$)\{$

l$2.$add$($f$.$apply$($x$))$;

$\}$

return l$2$;

$\}$

static List flatmap$($List l$,$ Function$>$ f$)\{$

$//$ walk through the U$\text{'}$s

$//$ use f at every stage f$.$apply

$//$ construct list of V$\text{'}$s

ArrayList res $=$ new ArrayList$<>()$;

for $($U x: l$)\{$

List l$2=$ f$.$apply$($x$)$;

for $($V y: l$2)\{$

res.add$($y$)$;

$\}$

$\}$

return res;

$\}$

$//$ foldleft$(0,[1,2,3,4],($x$,$y$)->$ x$+$y$)=10$

$//$ U $=$ V$=$ Integer

$//$ fpldleft$(1,[1,2,3,4],($x$,$y$)->$ x$*$y$)=24$

static V foldLeft$($V e$,$ Iterablel, BiFunction f$)\{$

$//$ walk through the U$\text{'}$s $[$u$1,$u$2,..,$un$]$

$//$ e

$//$ use f at every stage v$1=$ f$.$apply$($e$,$u$1)$

$//$ v$2=$ f$.$apply$($v$1,$u$2)$

$//$ v$3=$ f$.$apply$($v$2,$u$3)..$

$//$ return the last v

V v $=$ e;

for $($U x: l$)\{$

v $=$ f$.$apply$($v$,$x$)$;

$\}$

return v;

$\}$

$//$ similar to above

$//$ but from the right

$//$ vn$=$ f$($un$,$e$)$

$//$ vn$-1=$ f$($un$-1,$vn$)$

$//..$

$//$ return the first v

static V foldRight$($V e$,$ Listl, BiFunction f$)\{$

$//$ walk through the U$\text{'}$s $[$u$1,$u$2,..,$un$]$

$//$ e

$//$ use f at every stage v$1=$ f$.$apply$($u$1,$e$)$

$//$ v$2=$ f$.$apply$($u$2,$v$1)$

$//$ v$3=$ f$.$apply$($u$3,$v$2)..$

$//$ return the last v

V v $=$ e;

for $($int i $=$ l$.$size$()-1$; i $>=0$; i$--)\{$

v $=$ f$.$apply$($l$.$get$($i$),$v$)$;

$\}$

return v;

$\}$

$\}$