[Java Basics] Java data types - the third day of the 21-day learning plan

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Event address: CSDN 21-day learning challenge

The biggest reason for learning is to get rid of mediocrity. One day earlier, there will be more splendor in life; one day later, one day more mediocrity. Friends, let's work together!

type of data

1 Classification of Java language data types

• basic data type
• Reference data type (learn in depth when object-oriented)

2 Four categories and eight types of basic data types

type of data	keywords	memory usage	Ranges
integer	byte	1	Negative 2 to the 7th power ~ 2 to the 7th power -1 (-128~127)
	short	2	Negative 2 to the 15th power ~ 2 to the 15th power -1 (-32768~32767)
	int	4	Negative 2 to the 31st power ~ 2 to the 31st power -1
	long	8	Negative 2 to the 63rd power ~ 2 to the 63rd power -1
floating point number	float	4	1.401298e-45 ~ 3.402823e+38
	double	8	4.9000000e-324 ~ 1.797693e+308
character	char	2	0-65535
Boolean	boolean	1	true，false

illustrate

​ e+38 means multiplying by 10 to the 38th power, similarly, e-45 means multiplying by 10 to the negative 45th power.

​ In java, integers are of type int by default, and floating point numbers are of type double by default.

Need to remember the following points

The value range of byte type:

​ -128 ~ 127

Approximate value range of int type:

​ -More than 2.1 billion~ More than 2.1 billion

The relationship between the value range of integer type and decimal type:

​ double > float > long > int > short > byte

The most commonly used data type selection:

• When defining variables, different types of variables should be selected according to the actual situation.

  For example: the age of a person, you can choose the byte type.

  For example: the age of the earth, you can choose the long type.

• If the range of the integer type is not sure, then the int type is used by default.

• If the range of the decimal type is not sure, then the double type is used by default.

• If you want to define a variable of character type, then use char

• If you want to define a variable of Boolean type, then use boolean

3 Define 8 basic data type variables

public class VariableDemo3{
    
    
    public static void main(String[] args){
    
    
        //1.定义byte类型的变量
        //数据类型 变量名 = 数据值;
        byte a = 10;
        System.out.println(a);

        //2.定义short类型的变量
        short b = 20;
        System.out.println(b);

        //3.定义int类型的变量
        int c = 30;
        System.out.println(c);

        //4.定义long类型的变量
        long d = 123456789123456789L;
        System.out.println(d);

        //5.定义float类型的变量
        float e = 10.1F;
        System.out.println(e);

        //6.定义double类型的变量
        double f = 20.3;
        System.out.println(f);

        //7.定义char类型的变量
        char g = 'a';
        System.out.println(g);

        //8.定义boolean类型的变量
        boolean h = true;
        System.out.println(h);

    }
}

important point

• If you want to define a variable of integer type, you don't know which data type to choose, and int is used by default.
• If you want to define a variable of decimal type, you don’t know which data type to choose, and double is used by default.
• If you want to define a variable of type long, you need to add the L suffix after the data value. (Upper and lower case are acceptable, but upper case is recommended.)
• If you want to define a variable of type float, you need to add the F suffix after the data value. (both uppercase and lowercase)