Why is the "new" keyword so much more efficient than assignment?

I've got two methods to read in a string, and create Character objects:

static void newChar(String string) {
    int len = string.length();
    System.out.println("Reading " + len + " characters");
    for (int i = 0; i < len; i++) {
        Character cur = new Character(string.charAt(i));

    }       
}

and

static void justChar(String string) {
    int len = string.length();
    for (int i = 0; i < len; i++) {
        Character cur = string.charAt(i);

    }
}

When I run the methods using an 18,554,760 character string, I'm getting wildly different run times. The output I'm getting is:

newChar took: 20 ms
justChar took: 41 ms

With smaller input (4,638,690 characters) the time isn't as varied.

newChar took: 12 ms
justChar took: 13 ms

Why is new so much more efficient in this case?

EDIT:

My benchmark code is pretty hacky.

start = System.currentTimeMillis();
newChar(largeString);
end = System.currentTimeMillis();
diff = end-start;
System.out.println("New char took: " + diff + " ms");

start = System.currentTimeMillis();
justChar(largeString);
end = System.currentTimeMillis();
diff = end-start;
System.out.println("just char took: " + diff+ " ms");