Scala入门系列（四）：Map & Tuple

Map

1. 创建Map

   
   
   
 
    // 创建一个不可变的Map 
   
   
   
   

     scala> 
    val ages = 
    Map( 
    "Leo" -> 
    30, 
    "Sparks" -> 
    25) 
   
   
   
   

     ages: scala.collection.immutable. 
    Map[ 
    String, 
    Int] = 
    Map( 
    Leo -> 
    30, 
    Sparks -> 
    25) 
   
   
   
   
 
    // 创建一个可变的Map 
   
   
   
   

     scala> 
    val ages = scala.collection.mutable. 
    Map( 
    "Leo" -> 
    20, 
    "JEN" -> 
    23) 
   
   
   
   

     ages: scala.collection.mutable. 
    Map[ 
    String, 
    Int] = 
    Map( 
    JEN -> 
    23, 
    Leo -> 
    20) 
   
   
   
   

     scala> ages( 
    "Leo") = 
    31 
   
   
   
   
 
    // 使用另外一种方式定义Map元素 
   
   
   
   

     scala> 
    val ages = 
    Map(( 
    "leo", 
    30), ( 
    "sparks", 
    20)) 
   
   
   
   

     ages: scala.collection.immutable. 
    Map[ 
    String, 
    Int] = 
    Map(leo -> 
    30, sparks -> 
    20) 
   
   
   
   
 
    // 创建一个空的HashMap，必须是实现类而不是抽象接口 
   
   
   
   

     scala> 
    val ages = 
    new scala.collection.mutable. 
    HashMap[ 
    String, 
    Int] 
   
   
   
   

     ages: scala.collection.mutable. 
    HashMap[ 
    String, 
    Int] = 
    Map() 
   

 

2. 访问Map元素

   
   
   
 
    // 使用contains函数检查key是否存在 
   
   
   
   

     scala> 
    val leoAge = 
    if (ages.contains( 
    "Leo")) ages( 
    "Leo") 
    else 
    0 
   
   
   
   

     leoAge: 
    Int = 
    0 
   
   
   
   
 
    // getOrElse函数 
   
   
   
   

     scala> 
    val leoAge = ages.getOrElse( 
    "Leo", 
    0) 
   
   
   
   

     leoAge: 
    Int = 
    0 
   

 

3. 修改Map元素

   
   
   
 
    // 添加或者更新元素 
   
   
   
   

     scala> ages( 
    "Leo") = 
    31 
   
   
   
   
 
    // 添加多个元素 
   
   
   
   

     scala> ages += ( 
    "Mike" -> 
    34, 
    "Tom" -> 
    40) 
   
   
   
   
 
    // 移除元素 
   
   
   
   

     scala> ages -= 
    "Mike" 
   
   
   
   
 
    // 变相更新不可变map 
   
   
   
   

     scala> 
    val ages2 = ages + ( 
    "Mike" -> 
    34, 
    "Tom" -> 
    40) 
   

 

4. 遍历Map

   
   
   
 
    // 遍历map的entrySet 
   
   
   
   

     scala> 
    for((key, value) <- ages) println(key + 
    " " + value) 
   
   
   
   
 
    // 遍历key 
   
   
   
   

     scala> 
    for(key <- ages.keySet) println(key) 
   
   
   
   
 
    // 遍历value 
   
   
   
   

     scala> 
    for(value <- ages.values) println(value) 
   
   
   
   
 
    // 生成新map，反转key和value 
   
   
   
   

     scala> 
    for((key, value) <- ages) 
    yield (value, key) 
   

 

5. SortedMap & LinkedHashMap

   
   
   
 
    // SortedMap可以自动对Map的key排序，按照字母顺序 
   
   
   
   

     scala> 
    val ages = scala.collection.immutable. 
    SortedMap( 
    "leo" -> 
    30, 
    "alice" -> 
    15) 
   
   
   
   

     ages: scala.collection.immutable. 
    SortedMap[ 
    String, 
    Int] = 
    Map(alice -> 
    15, leo -> 
    30) 
   
   
   
   
 
   
   
   
   
 
    // LinkedHashMap可以记住插入entry的顺序 
   
   
   
   

     scala> 
    val ages = 
    new scala.collection.mutable. 
    LinkedHashMap[ 
    String, 
    Int] 
   
   
   
   

     ages: scala.collection.mutable. 
    LinkedHashMap[ 
    String, 
    Int] = 
    Map() 
   
   
   
   

     scala> ages( 
    "leo") = 
    30 
   
   
   
   

     scala> ages( 
    "Sparks") = 
    20 
   
   
   
   

     scala> ages 
   
   
   
   

     res70: scala.collection.mutable. 
    LinkedHashMap[ 
    String, 
    Int] = 
    Map(leo -> 
    30, 
    Sparks -> 
    20) 
   

 

元组Tuple

Scala元组将固定数量的项目组合在一起，以便它们可以作为一个整体传递。 与数组或列表不同，元组可以容纳不同类型的对象，但它们也是不可变的。（可以用作自定义数据类型）

   
   
   
 
    // 创建Tuple 
   
   
   
   

     scala> 
    val t = ( 
    "leo", 
    30, 
    "hello") 
   
   
   
   

     t: ( 
    String, 
    Int, 
    String) = (leo, 
    30,hello) 
   
   
   
   
 
    // 访问Tuple 
   
   
   
   

     scala> t._1 
   

 

   
   
   
 
    // zip操作 
   
   
   
   

     scala> 
    val names = 
    Array( 
    "leo", 
    "jack", 
    "mike") 
   
   
   
   

     names: 
    Array[ 
    String] = 
    Array(leo, jack, mike) 
   
   
   
   
 
   
   
   
   

     scala> 
    val ages = 
    Array( 
    30, 
    24, 
    25) 
   
   
   
   

     ages: 
    Array[ 
    Int] = 
    Array( 
    30, 
    24, 
    25) 
   
   
   
   
 
   
   
   
   

     scala> 
    val nameAges = names.zip(ages) 
   
   
   
   

     nameAges: 
    Array[( 
    String, 
    Int)] = 
    Array((leo, 
    30), (jack, 
    24), (mike, 
    25)) 
   
   
   
   
 
   
   
   
   

     scala> 
    for ((name, age) <- nameAges) println(name + 
    ":" + age) 
   
   
   
   

     leo: 
    30 
   
   
   
   

     jack: 
    24 
   
   
   
   

     mike: 
    25