identifier

        Definition ： It's for the class , Method , Variables and other named symbols .

        The rules ：1. It's numbers , Letter , Dollar sign and underline （—） form .

                   2. Cannot start with a number

                   3. Cannot be keyword

                   4. Be case sensitive

        Common naming rules ：

            Naming of small hump ： Mainly for methods and variables

                1. When the identifier is a word , title case .

                2. When an identifier consists of multiple words , First word initial lowercase , Capitalize other words .

            The name of the great hump ： Mainly for class

                1. When the identifier is a word , title case .

                2. When an identifier consists of multiple words , Capitalize each word .

            See the name and know the meaning

Type conversion

        classification ： Automatic conversion , Coercive transformation

Data types are small to large

            char(16)

byte(8)-----short(16)-----int(32)-----long(64)-----float(32)-----double(64)

among char Convert directly to int type , Cannot be converted to byte and short type .

Don't forget int Type can be directly converted to double type .

Automatic conversion type ： Assign a value or variable that represents a small range of data to another variable that represents a large range of data .

        Automatic conversion type is low-level and can be directly converted to high-level

public class change{
    public static void main(String[]args){
        int a = 10:;
        System.out.println(a);
        double b =10;
        System.out.println(b);
        // among a The output number will be 10, however b The output is 10.0
        // This is it. int Type is automatically converted to double
    
    }
}

                 In fact, you can also experiment byte turn short This automatic conversion .

                 remember byte and short Cannot convert to char Type of yo .

        Coercive transformation ： Assign a data or variable representing a large data range to another variable representing a small data range .

                Format ： Target data type     Variable name   =  （ Target data type ） Values or variables

Public class change{
    public static void main (String []args){
        // Define a double The number of types is strongly changed to int type 
     //int c = 66.66;
      // System.out.println(c);
        // If it is written in this way, it will show incompatibility, so it is wrong and should be forced to 
        int a = (int)66.66;
        System.out.println(a);
    
    }
}

                The above code error has been shielded , The following strong rotation can be run .

             But the one bad thing about forced conversion is that there will be data loss . Just like up here 66.66 Convert to int After the type, there is only 66 了 .