BrownWong的专栏

1. OverviewAlmost all “operators” are actually methods. Consider this most basic of examples: 1 + 2 That plus sign between the numbers? It’s a method.1 + 2 is the same as 1.+(2), because of the “infi

scala code exampleclass Upper { def upper(strings: String*): Seq[String] = { strings.map((s:String) => s.toUpperCase()) }}val up = new Upperprintln(up.upper("Hello", "World!"))In Sc

Semicolons are expression delimiters and they are inferred. Scala treats the end of a line as the end of an expression, except when it can infer that the expression continues to the next line, as in th

Scala allows you to decide whether a variable is immutable (read-only) or not (readwrite) when you declare it. immutable “variable”an immutable “variable” is declared with the keyword val (think value

Sometimes we need a sequence of numbers from some start to finish. A Range literal is just what we need. The following examples show how to create ranges for the types that support them, Int, Long, Flo

1.DefinitionPartial functions are partial in the sense that they aren’t defined for all possible inputs, only those inputs that match at least one of the specified case clauses.Only case clauses can be

The scala.concurrent.Future API uses implicit arguments to reduce boilerplate in your code. They are another tool for concurrency provided by Scala. Akka uses Futures, but you can use them separately w

1. OverviewSome functional programming languages, like Haskell, can infer almost all types, because they can perform global type inference. Scala can’t do this, in part because Scala has to support sub

Table lists the reserved keywords in Scala. Many are found in Java and they usually have the same meanings in both languages. Word Description abstract Makes a declaration abstract. case Sta

Integer LiteralsInteger literals can be expressed in decimal, hexadecimal, or octal.You indicate a negative number by prefixing the literal with a – sign.For Long literals, it is necessary to append th

Most languages have a special keyword or type instance that’s assigned to reference variables when there’s nothing else for them to refer to. In Java, it’s null, which is a keyword, not an instance of

A key point about Option is that there are really only two valid subtypes. Either we have a value, the Some case, or we don’t, the None case. There are no other subtypes of Option that would be valid.

Scala adopts the package concept that Java uses for namespaces, but Scala offers more flexibility. Filenames don’t have to match the type names and the package structure does not have to match the dire

1. Four ways to importThere are four ways to import:Import all types in a package, using the underscore(_) as a wildcard. e.g. import java.awt._Import individual Scala or Java types. e.g. import j

1. Values, Variables, and Types in Matches(1) BasicLet’s cover several kinds of matches. The following example matches on specific values, all values of specific types, and it shows one way of writing

There are three kinds of interpolated strings.A String of the form s"foo ${bar}" will have the value of expression bar, converted to a String and inserted in place of ${bar}. If the expression bar ret

What characters can you use in identifiers? Here is a summary of the rules for identifiers, used for method and type names, variables, etc:Characters Scala allows all the printable ASCII characters

When a function returns Unit it is totally side-effecting. There’s nothing useful that can be done with Unit, so the function can only perform side effects on some state, either globally, like performi

1. Methods with Empty Argument ListsIf a method takes no parameters, you can define it without parentheses. Callers must invoke the method without parentheses. Conversely, if you add empty parentheses

If an expression like 2.0 * 4.0 / 3.0 * 5.0 is actually a series of method calls on Doubles.Here they are in order from lowest to highest precedence:1. All letters2. |3. ^5. < >6. = !7. :8. + -9

What’s different in Scala is that if statements and almost all other statements in Scala are actually expressions that return values. If it’s true, then the corresponding block is evaluated. Otherwise

The term comprehension comes from functional programming. It expresses the idea that we are traversing one or more collections of some kind, “comprehending” what we find, and computing something new fr

In Java, == compares object references only. It doesn’t perform a logical equality check. You use the equals method for that purpose. In contrast, Scala uses == for logical equality, but it calls the e

用cmd编译和运行scala脚本。脚本内容： Decla.scalaobject Decla{ def main(args: Array[String]){ var myVar : Int = 10 val myVal : String = "Hello Scala" var myVar1 = 20 val myVal1 =

Scala encourages a coding style that lessens the need for exceptions and exception handling. But exceptions are still used, especially where Scala interacts with Java code, where use of exceptions is m

Method Default and Named ArgumentsHere is an example:package com.brown/** * Created by BrownWong on 2016/9/29. */case class Point(x: Double=0.0, y: Double=0.0){ def shift(deltaX: Double=0.0, delt

1. DescriptionTypically, parameters to functions are by-value parameters; that is, the value of the parameter is determined before it is passed to the function. But what if we need to write a functi

1. DescriptionA related scenario to by-name parameters is the case where you want to evaluate an expression once to initialize a value, not repeatedly, but you want to defer that invocation. There are

While enumerations are a built-in part of many programming languages, Scala takes a different route and implements them as an Enumeration class in its standard library. You just define an object that

1. Parameterized typesScala supports parameterized types, which are very similar to generics in Java. Java uses angle brackets (<…>), while Scala uses square brackets ([…]), because < and > are often u