public class Lock

$\{$

private String combination $="0042"$;

private String input $=""$;

$/**$

Simulates a digit button push.

@param button a digit $0...9$

$*/$

public void push$($int button$)$

$\{$

$/*$ Your code goes here $*/$

input $=$ input $+$ button;

$\}$

$/**$

Simulates a push of the open button.

@return true if the lock opened

$*/$

public boolean open$()$

$\{$

$/*$ Your code goes here $*/$

return input.equals$($combination$)$;

$\}$

$\}$