This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
s.equals(t) will work since s.equals(t) will compare the values. s == t will compare the objects in the heap. s == u will generate a compilation error. t.equals(u) are not equals since the values are different.