JAVA programming 問題

public class Main {

public static void main(String[] args){

String date = "01/01/2001";

String first = date.substring(2, 3);
String second = date.substring(5, 6);

System.out.println(first+second);

if (first=="/")
System.out.println("first ok");
if (second=="/")
System.out.print("second ok");
}

}

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以上未能print out 最後的"first ok"以及"second ok"
但System.out.println(first+second)中print out的確實是兩個"/"
請問問題出在哪？