文档地址：

https://developer.apple.com/library/prerelease/content/documentation/Swift/Conceptual/Swift_Programming_Language/StringsAndCharacters.html#//apple_ref/doc/uid/TP40014097-CH7-ID285

1、Initializing an Empty String

var emtyString = “”

var anotherEmptyString = String()

两种初始化方法

2、Find out whether a String value is empty by checking its Boolean isEmpty property

if emptyString.isEmpy {

print(“Nothing to see here”)

}

3、override 计算机里面是覆盖的意思

4、变量能修改，常量不能修改，这个与oc里面的字符串不一样

5、for character in “Dog!