Scala-1.字符串

0 引言

打印一个字符串的类型名，就是java.lang.String:

scala> "hello".getClass.getName
res0: String = java.lang.String

Java的String类的方法就都可以用了。例如字符串长度和连接：

scala> "hello".getClass.getName
res0: String = java.lang.String

scala> val s = "hello"
s: String = hello

scala> s.length
res1: Int = 5

scala> val s = "hello" + " world"
s: String = hello world

String类有StringOps类中的方法，例如foreach：

scala> "hello".foreach(println)
h
e
l
l
o

for循环处理也可以：

scala> for (c <- "hello") println(c)
h
e
l
l
o

也可以当做字符串序列：

scala> "hello".getBytes.foreach(println)
104
101
108
108
111

1. 字符串相等

和Java不同。Scala直接用==就行了,也不怕null，但是不能在null上调用方法：

scala> "hello" == "hello"
res7: Boolean = true

scala> "hellp" == "h" + "llo"
res8: Boolean = false

scala> "hello" == "h" + "llo"
res9: Boolean = false

scala> "hello" == "h" + "ello"
res10: Boolean = true

scala> "hello" == "Hello".toLowerCase
res11: Boolean = true

scala> null == "hello"
res12: Boolean = false

scala> "hello" == null.toLowerCase
<console>:12: error: value toLowerCase is not a member of Null
       "hello" == null.toLowerCase

2. 创建多个字符串

三个引号能创建多行字符串，甚至包含开头的空格。有一个stripMargin方法去掉编码时为了视觉方便添加的空格，该方法默认以|作为标志，可以设定参数。

scala> val s1 = """ This is
     | a Mulitline
     | String"""
s1: String =
" This is
a Mulitline
String"

scala> val s2 = """This is 
     |                  #a Multiline
     |                  #line""".stripMargin('#')
s2: String =
This is
a Multiline
line

3. 分隔字符串

和很多其他语言一样，用split，不同的使用细节会有一些不同的结果，不详述：

scala> "hello world".split(" ")
res14: Array[String] = Array(hello, world)

4. 变量替换

就是格式化吧，java中format的一套：

scala> val name = "John"
name: String = John

scala> val age = 28
age: Int = 28

scala> println(s"$name is $age years old")
John is 28 years old

可以再字符串变量汇总使用表达式：

scala> println(s"Age next year ${age + 1}")
Age next year 29
scala> println(s"Age next year are 30 are ${age==30}")
Age next year are 30 are false

表达式可以用于对类的成员引用：

scala> println(s"A student named ${hanna.name} has a score of ${hanna.score}" )
A student named hanna has a score of 95

s实际上是一个方法，类似的方法就还有f：

scala> println(f"A student named ${hanna.name} has a score of ${hanna.score}%.1f")
A student named hanna has a score of 95.0

raw插入符不转义

scala> println(raw"foo\bar")
foo\bar

格式化常用符：
%c %d %e %f %I %o %s %u %x %% %