variable initialized in class loses its previous value with the page loading

I’ve declared a String variable test with “hi”. every time I click on Button1, I expect that test will be appended with its previous value. But I have noticed that it loses its previous value when the button is clicked and the page is reloaded. That is every time I click it, it has its text as “hihi”. I expect “hihihihi” on the next click and so on. What’s the problem here with the code below?