intern() behaving differently in Java 6 and Java 7

class Test {
    public static void main(String...args) {
        String s1 = "Good";
        s1 = s1 + "morning";
        System.out.println(s1.intern());
        String s2 = "Goodmorning";
        if (s1 == s2) {
            System.out.println("both are equal");
        }
    }
}

This code produces different outputs in Java 6 and Java 7. In Java 6 the s1==s2 condition returns false and in Java 7 the s1==s2 returns true. Why?

Why does this program produces different output in Java 6 and Java 7?