I am trying to use Java GUI swing to make a tic$-$tac$-$toe game. It looks like there is something wrong with my checkWinner$()$ method. It checks the rows just fine, but besides the first column, other column wins and diagonal wins aren't being detected and I can't figure out why. I've attached my entire code for context and would appreciate any help to solve my issue.

public toe$()\{$

setTitle$("$Tic Tac Toe"$)$; $//$sets title of the game

setSize$(500,500)$;

getContentPane$().$setBackground$($new Color$(50,50,50))$;

setDefaultCloseOperation$($JFrame$.$EXIT$\_$ON$\_$CLOSE$)$;

mainFrame $=$ new JPanel$($new BorderLayout$())$;

gameBoard $=$ new JPanel$($new GridLayout$(3,3))$; $//$sets the icon lay out to be $3$ rows of $3$

gameBoard.setPreferredSize$($new Dimension$(500,500))$;

add$($mainFrame$)$;

mainFrame.add$($textField$,$ BorderLayout.NORTH$)$;

mainFrame.add$($gameBoard$,$ BorderLayout.CENTER$)$;

resetButton $=$ new JButton$("$Reset$")$;

mainFrame.add$($resetButton$,$ BorderLayout.SOUTH$)$;

resetButton.addActionListener$($this$)$;

buttons $=$ new JButton$[3][3]$;

determineFirstPlayer$()$;

iconX $=$ new ImageIcon$("$starfish$.$png$")$;

iconO $=$ new ImageIcon$("$fish$.$png$")$;

makeButtons$()$; $//$calls a seperate method that makes all the buttons

setVisible$($true$)$;

$\}$

public void determineFirstPlayer$()\{$

if $($Math$.$random$()<0\mathrm{.}5)\{$

currentPlayer $="$X$"$;

$\}$ else $\{$

currentPlayer $="$O$"$;

$\}$

textField.setText$("$Player $"+$ currentPlayer $+"$ plays."$)$;

$\}$

private void makeButtons$()\{$

$//$nested for loops to make all $9$ buttons

for $($int i $=0$; i $<3$; i$++)\{$

for $($int j $=0$; j $<3$; j$++)\{$

buttons$[$i$][$j$]=$ new JButton$()$;

gameBoard.add$($buttons$[$i$][$j$])$;

buttons$[$i$][$j$].$addActionListener$($this$)$;

$\}$

$\}$

$\}$

private boolean checkWinner$()\{$

$//$checking rows

for $($int i $=0$; i $<3$; i$++)\{$

if $($

$($buttons$[$i$][0].$getIcon$()!=$ null$)$ && $($buttons$[$i$][0].$getIcon$().$equals$($buttons$[$i$][1].$getIcon$()))$ &&

$($buttons$[$i$][0].$getIcon$().$equals$($buttons$[$i$][2].$getIcon$())))\{$

return true;

$\}$

$\}$

$//$columns

for $($int i $=0$; i $<3$; i$++)\{$

if $($

$($buttons$[0][$i$]!=$ null$)$ && $($buttons$[0][$i$].$getIcon$().$equals$($buttons$[1][$i$].$getIcon$()))$ &&

$($buttons$[0][$i$].$getIcon$().$equals$($buttons$[2][$i$].$getIcon$())))\{$

return true;

$\}$

$\}$

$//$checking diagonals

if $($

$($buttons$[0][0].$getIcon$()!=$ null$)$ && $($buttons$[0][0].$getIcon$().$equals$($buttons$[1][1].$getIcon$()))$ &&

$($buttons$[0][0].$getIcon$().$equals$($buttons$[2][2].$getIcon$())))\{$

return true;

$\}$

else if $($

$($buttons$[0][2].$getIcon$()!=$ null$)$ && $($buttons$[0][2].$getIcon$().$equals$($buttons$[1][1].$getIcon$()))$ &&

$($buttons$[0][2].$getIcon$().$equals$($buttons$[2][0].$getIcon$())))\{$

return true;

$\}$

return false;

$\}$

private boolean isBoardFull$()\{$

$//$if the board gets full and theres no winner

for $($int i $=0$; i $<3$; i$++)\{$

for $($int j $=0$; j $<3$; j$++)\{$

if $($buttons$[$i$][$j$].$getIcon$()==$ null$)\{$

return false;

$\}$

$\}$

$\}$

$//$if all buttons are full, then the board is full and the return is true.

return true;

$\}$

private void resetGame$()\{$

determineFirstPlayer$()$;

for $($int i $=0$; i $<3$; i$++)\{$

for $($int j $=0$; j $<3$; j$++)\{$

buttons$[$i$][$j$].$setIcon$($null$)$;

$\}$

$\}$

$\}$

@Override

public void actionPerformed$($ActionEvent event$)\{$

JButton clickedButton $=($JButton$)$ event.getSource$()$;

if $($clickedButton $==$ resetButton$)\{$

resetGame$()$;

$\}$ else $\{$

if $($clickedButton$.$getIcon$()==$ null$)\{$

$//$sets icon for the current player

if $($currentPlayer$.$equals$("$X$"))\{$

clickedButton.setIcon$($iconX$)$;

currentPlayer $="$O$"$; $//$switches to next player

$\}$ else $\{$

clickedButton.setIcon$($iconO$)$;

currentPlayer $="$X$"$; $//$switched to next player

$\}$

textField.setText$("$Player $"+$ currentPlayer $+"$ plays."$)$;

$//$checking if there is a winner or draw

if $($checkWinner$())\{$

String winner;

if $($currentPlayer$.$equals$("$X$"))\{$

winner $="$O$"$;

$\}$ else $\{$

winner $="$X$"$;

$\}$

JOptionPane.showMessageDialog$($this$,$ winner $+"$ wins!"$)$;

resetGame$()$