A. Variables and basic data structures

1. There are two types of variables in Scala: mutable variables and immutable variables, variable variables using the keyword var definition, immutable variables defined by Val;

Variables defined in 2.Scala must initialize the assignment, you can use the placeholder (_) to initialize, the base type string using "_" after initialization is null,float/double/int after initialization for 0,char after initialization? (Note: Placeholders cannot be used in the method declaration);

3. Variables that use the keyword lazy modifier are assigned only when they are actually used, but lazy can only modify a Val-type variable (to be re-assigned if the variable is not used while the program is running);

4.Float type data must be appended with f/f after the floating-point number, otherwise it will be deduced as double by type;

5.Double types of data can be expressed as an exponent, for example: 0.31415e1 = = 3.1415;

The 6.Char type is wrapped in single quotes, with special characters using the escape character (\) or Unicode encoding;

7.String type use three double quotation marks ("" ") package can be output as is;

The 8.Scala provides a +,-symbol to represent positive negative numbers, and can be used directly for calculation;

9.Scala Use = = comparison is based on content rather than references!!! For example: "hi" = = new String ("HI") and 1 = = 1.0 all return true, but 1 = = "1" returns false;

The String defined in 10.Scala is based on java.lang.String, so the methods in Java.lang.String are available, and some new methods are encapsulated in implicit conversions. For example: reverse, map, drop, slice and so on;

11. Operator precedence is similar to Java, where there are multiple priority operations performed from left to right, but::(list constructs) and::(list concatenation) is an exception! ；

12. Tuples can put different types in the same variable, through the variable name. _n (N is the index number, starting from 1), you can also extract the contents of the tuple and initialize the variables. For example: 1. var tuple = ("Hello", ' Cheng ', 1), tuple._1 = "Hello", 2. Val (first,second,third) = tuple,first:string = Hello,second:string = Cheng;

13. Symbol type definition need to use ' symbol, mainly play the role of identification, re-match, content judgment is more commonly used;

A. Variables and basic data structures