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Pattern matching before jdk1.7, Java's switch keyword can only handle native types (int, short, byte, char) and enumerated types. After jdk1.7, switch added handling of the String type.

Scala's pattern matching can handle a variety of complex types and scenarios. Constant matching, variable matching, list and tuple matching

In the last line of instruction, _ is a wildcard, which ensures that we can handle all cases. Otherwise, when you pass in a value that cannot be matched, you will get a runtime error.

Nil is an empty List, defined as List [Nothing].

Type matching

The case clause supports "OR" logic. Use |; closure

A closure is a function and the return value depends on one or more variables declared outside the function.

Generally speaking, a closure can be simply thought of as another function that can access local variables in a function.

For example, the function: val multiplier = (i:Int) = > I * factor;factor is not a formal parameter, but a free variable; the defined function variable multiplier becomes a "closure" because it refers to the variable defined outside the function, and the process of defining this function is to capture the free variable to form a closed function.

Corialization function

The process of changing a function that takes two parameters into a new function that takes one parameter. The new function returns a function that takes the original second argument as an argument.

Def sum (x:Int) (y:Int) = def sum, and after Corification, it is called Corey.

What does this function mean? Receives an x as an argument and returns an anonymous function, which is defined as receiving an int parameter y and the function body is xroomy

Partial function and partial Application function

A partial function is not a function. The Partia Function in Scala is a Trait of type PartialFunction [A _ Magi B], which receives an argument of type An and returns a result of type B.

There are some methods inside the partial function, such as isDefinedAt, OrElse, andThen, applyOrElse

IsDefinedAt: determine whether the passed parameter is within the processing range. OrElse: combine multiple partial functions to achieve a similar effect as the case statement. AndThen: equivalent to successive calls to a method, such as g (f (x)). ApplyOrElse: it takes two arguments, the first is the called parameter, and the second is a callback function. If the parameters of the first call match, the matching value is returned, otherwise the callback function is called.

Partial application function means that a function has n parameters, and we provide it with less than n parameters, then we get a partial application function.

Object and class

There is no static keyword in scala

So for a class, all methods and member variables are inaccessible until the instance is new.

All member variables and methods in scala object are static by default

So only the main method in object can be accessed directly.

Collection in scala

Map definition: var verMap = Map [String, String] ()

Map add element: verMap + = (mapKey-> categeryName)

List definition: var listNewValue: List [String] = List ()

List add element: listNewValue: + = mulValue

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