Scala provides a powerful pattern matching mechanism and has a wide range ofapplications.
A pattern match contains a series of alternatives, each starting with a keyword case . Each alternative contains a pattern and one or more expressions. The arrow symbol => patterns and expressions are separated.
The following is a simple example of integer value pattern matching: Execute the above code, and the output is as follows: Next, let’s look at a pattern matching of different data types: Execute the above code, and the output is as follows: The first in the instance The class definition that uses the case keyword is the case classes, which is a special class that is optimized for pattern matching. The following is a simple example of the sample class: Execute the above code, and the output is as follows: The following process occurs automatically when the sample class is declared: Each parameter of the constructor becomes Provided in the companion object Provide Generate
In recent years, Geographic Information Systems (GIS) have undergone rapid development in both theoretical and practical dimensions. GIS has been widely applied for modeling and decision-making support across various fields such as urban management, regional planning, and environmental remediation, establishing geographic information as a vital component of the information era. The introduction of the “Digital Earth” concept has further accelerated the advancement of GIS, which serves as its technical foundation. Concurrently, scholars have been dedicated to theoretical research in areas like spatial cognition, spatial data uncertainty, and the formalization of spatial relationships. This reflects the dual nature of GIS as both an applied technology and an academic discipline, with the two aspects forming a mutually reinforcing cycle of progress. 8.38.1. Example #
object Test {
def main(args: Array[String]) {
println(matchTest(3))
}
def matchTest(x: Int): String = x match {
case 1 => "one"
case 2 => "two"
case \_ => "many"
}
}
$ scalac Test.scala
$ scala Test
many
Match corresponds to switch in Java, but is written after the selector expression. Namely: selector match {alternative}. match expressions are evaluated by trying each pattern in the order in which they are written, as long as a matching case , the rest. case will not continue to match. 8.38.2. Example #
object Test {
def main(args: Array[String]) {
println(matchTest("two"))
println(matchTest("test"))
println(matchTest(1))
println(matchTest(6))
}
def matchTest(x: Any): Any = x match {
case 1 => "one"
case "two" => 2
case y: Int => "scala.Int"
case \_ => "many"
}
}
$ scalac Test.scala
$ scala Test
2
many
one
scala.Int
case corresponding to the integer value 1, the second case , the corresponding string value two, the third case .The corresponding type pattern, which is used to determine whether the passed value is an integer, compared to using the isInstanceOf to determine the type, it is better to use pattern matching. The fourth case indicates the default full-match option, that is, if no other matchis found, similar to switch in default .Use sample classes #
8.38.3. Example #
object Test {
def main(args: Array[String]) {
val alice = new Person("Alice", 25)
val bob = new Person("Bob", 32)
val charlie = new Person("Charlie", 32)
for (person <- < span> List(alice, bob, charlie)) {
person match {
case Person("Alice", 25) => println("Hi Alice!")
case Person("Bob", 32) => println("Hi Bob!")
case Person(name, age) =>
println("Age: " + age + " year, name: " + name + "?")
}
}
}
// Sample Class
case class Person(name: String, age: Int)
}
$ scalac Test.scala
$ scala Test
Hi Alice!
Hi Bob!
Age: 32 year, name: Charlie?
val unless explicitly declared as var , but this is not recommended apply method, so you don’t have to use the new keyword to build an object unapply method to make pattern matching work toString 、 equals 、 hashCode and copy methods, unless the definition of these methods is shown.
Principles, Technologies, and Methods of Geographic Information Systems
102