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How many constants and data types do you remember?

2022-08-10 11:56:00 【51CTO】

前言

In our last post we were talking aboutjavaNotes in the base,关键字,和标识符,这篇我们讲一下javaBasic constants and data types,This series is in strict accordance with thejava学习大纲,A series of step-by-step updates,Brothers who are beginners can pay attention,本系列持续更新.

Do you remember how many constants and the data type？_数据类型

1.介绍

java中,有许多,All kinds of data need us to represent,有的是可变的,some can't be changed,所以javadeclares two types to describe our data,一个是常量（不可改变的量,如常见的：1,2,1.5,2.7等）,一个是变量（可以改变的量）.

“常量”的广义概念是：‘不变化的量’（利如：在计算机程序运行时,不会被程序修改的量;数学函数中的某一个量,例如每一个具体的圆的半径、直径数值;物理学中的靠近地面的重力加速度;真空中的光速数值;不同的微粒的各自的质量）换言之,常量,在计算机技术方面虽然是为了硬件、软件、编程语言服务,但是它并不是专门为硬件、软件、编程语言而引入的概念.常量可区分为不同的类型,如：25、0、-8为整型常量,6.8、-7.89为实型常量,‘a’、‘b’为字符常量.常量一般从其字面形式即可判断.这种常量称为字面常量或直接常量.

2.常量

2.1、常量概念

常量是不能改变的量,That is, each constant is a value.

3、数据类型

Just like in mathematics, there are two types of numbers: decimals and integers,在JavaIt needs to represent the diverse content in life and production,Its data types are richer than decimals and integers in mathematics.

Javais a strongly typed language that strictly distinguishes data types,That is, each data must have a data type.

3.1、整数

（1）十进制表示方式：正常数字,如 13、25等

（2）二进制表示方式：以0b(0B)开头,如0b1011 、0B1001

（3）十六进制表示方式：以0x(0X)开头,数字以0-9及A-F组成,如0x23A2、0xa、0x10

（4）八进制表示方式：以0开头,如01、07、0721

代码演示：

       
       public 
       
       class 
       
       Main{
       
       //磊哥的java历险记@51博客
       
       public 
       
       static 
       
       void 
       
       main(
       
       String[] 
       
       args){
       
       //整数 
       
       //十进制:常用 
       
       System.
       
       out.
       
       println(
       
       8);
       
       //二进制:以0b/0B开头 只包含0和1 
       
       System.
       
       out.
       
       println(
       
       0b1000);
       
       //十六进制:以0x/0X开头 0-9 a-f 
       
       System.
       
       out.
       
       println(
       
       0x8);
       
       System.
       
       out.
       
       println(
       
       0xb);
       
       //八进制:以0开头 0-7 
       
       System.
       
       out.
       
       println(
       
       010);
       
       //8 
       
       System.
       
       out.
       
       println(
       
       011);
       
       //9 
       
       System.
       
       out.
       
       println(
       
       017);
       
       //15 
       
    }
       
}
      
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Do you remember how many constants and the data type？_数据类型_02

3.2、小数

如2.13、1.0,0.5.

代码演示：

       
       public 
       
       class 
       
       Main{
       
       //磊哥的java历险记@51博客
       
       public 
       
       static 
       
       void 
       
       main(
       
       String[] 
       
       args){
       
       //小数 
       
       System.
       
       out.
       
       println(
       
       3.1415926);
       
    }
       
}
      
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Do you remember how many constants and the data type？_常量_03

3.3、布尔型

Used to indicate whether,布尔类型只有两个值 trueRepresents true that the condition is satisfied, false代表假,即不满足条件.

代码演示：

       
       public 
       
       class 
       
       Main{
       
       //磊哥的java历险记@51博客
       
       public 
       
       static 
       
       void 
       
       main(
       
       String[] 
       
       args){
       
       //布尔 
       
       System.
       
       out.
       
       println(
       
       true);
       
       System.
       
       out.
       
       println(
       
       false);
       
    }
       
}
      
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Do you remember how many constants and the data type？_数据类型_04

3.4、字符

3.4.1、普通字符

（1）表示单个字符,The keys of the keyboard can enter a character.A Chinese character can represent a character.

（2）characters need to be used’’将内容包裹

（3）Character content cannot be empty

如 ‘1’、 ‘a’、 ‘ ’(空格)、 ‘中’、 ‘$’

代码演示：

       
       public 
       
       class 
       
       Main{
       
       //磊哥的java历险记@51博客
       
       public 
       
       static 
       
       void 
       
       main(
       
       String[] 
       
       args){
       
       //字符 必须用''包裹起来 不能为空 
       
       System.
       
       out.
       
       println(
       
       '1');
       
       System.
       
       out.
       
       println(
       
       'a');
       
       System.
       
       out.
       
       println(
       
       'B');
       
       // System.out.println('磊哥');//错误: 未结束的字符文字 
       
       System.
       
       out.
       
       println(
       
       '&');
       
    }
       
}
      
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Do you remember how many constants and the data type？_数据类型_05

语法错误：

出现语法错误,IDEA会报红,Alerts you to grammatical errors

Do you remember how many constants and the data type？_Java基础_06

如果报错,我们没注意到,Is forced to perform,The code will not compile,and will give us more obvious hints

Do you remember how many constants and the data type？_常量_07

3.4.2、转义字符

Sometimes we cannot give a character directly,Need to use escape character for escape action.转义字符也为一个字符,The escape symbol is composed of the escape symbol and the escaped character：\

如:

\t 制表符,print out the least1个,最多8个空格

\' 单引号,打印出‘

\" 双引号,打印出"

\\ 反斜杠,打印出 \

Do you remember how many constants and the data type？_数据类型_08

代码演示：

       
       public 
       
       class 
       
       Main{
       
       //磊哥的java历险记@51博客
       
       public 
       
       static 
       
       void 
       
       main(
       
       String[] 
       
       args){
       
       //Cannot give a character directly,Need to use escape character for escape action 
       
       System.
       
       out.
       
       println(
       
       '\t'); 
       
       // \t 制表符,print out the least1个,最多8个空格 
       
       System.
       
       out.
       
       println(
       
       "a");
       
       System.
       
       out.
       
       println(
       
       '\r');
       
       // \r 回车 
       
       System.
       
       out.
       
       println(
       
       'b');
       
       System.
       
       out.
       
       println(
       
       'c');
       
       System.
       
       out.
       
       println(
       
       'd');
       
    }
       
}
      
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Do you remember how many constants and the data type？_Java基础_09

3.4.3、字符串

（1）字符串String是一种特殊的数据类型

（2）字符串必须使用“”包裹

如 “我爱Java”、 “0”、 “a”、 “”、 “null”

代码演示：

       
       public 
       
       class 
       
       Main{
       
       //磊哥的java历险记@51博客
       
       public 
       
       static 
       
       void 
       
       main(
       
       String[] 
       
       args){
       
       //字符串 必须用""包裹起来
       
       System.
       
       out.
       
       println(
       
       "磊哥java历险记!");
       
       System.
       
       out.
       
       println(
       
       " ");
       
    }
       
}
      
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Do you remember how many constants and the data type？_java_10

3.5、null常量

used in object-oriented,He means that the value isnull,并不是没有,只有一个值,Is mainly used to fight for the reference data type.【null】

3.6、符号常量

用finalModified variables are symbolic constants

格式:final 变量类型变量名（大写）=初始化值;

比如：Our name,We basically won't change the name after we've chosen it.,but the name is often used,all we can define as symbolic constants.

代码演示：

       
       public 
       
       class 
       
       Main{
       
       //磊哥的java历险记@51博客
       
       public 
       
       static 
       
       void 
       
       main(
       
       String[] 
       
       args){
       
       //定义一个name常量
       
       final   
       
       String 
       
       Name 
       
       =
       
       "磊哥java历险记";
       
       //打印
       
       System.
       
       out.
       
       println(
       
       Name);
       
    }
       
}
      
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展示：

Do you remember how many constants and the data type？_java_11

What if we want to change the name later?？能改吗?Let's take a look：

Do you remember how many constants and the data type？_java_12

我们能看到,不符合java语法,编译不通过.

4.Three types of constants

常量有三种类型：静态常量、成员常量和局部常量.

静态常量：

使用在 final 之前 public static 修饰.public static 修饰的常量作用域是全局的,不需要创建对象就可以访问它,在类外部访问形式为 HelloWorld. PI.这种常量在编程中使用很多.

成员常量：

作用域类似于成员变量,不能修改.

局部常量：

作用域类似于局部变量,不能修改.

在定义常量时就需要对该常量进行初始化.

final 关键字不仅可以用来修饰基本数据类型的常量,还可以用来修饰对象的引用或者方法.

为了与变量区别,常量取名一般都用大写字符.

代码演示：

       
       public 
       
       class 
       
       Main{
       
       //磊哥的java历险记@51博客
       
       // 静态常量 
       
       public 
       
       static 
       
       final 
       
       String 
       
       name 
       
       = 
       
       "磊哥java历险记";
       
       // 声明成员常量 
       
       final 
       
       int 
       
       y 
       
       = 
       
       10;
       
       public 
       
       static 
       
       void 
       
       main(
       
       String[] 
       
       args){
       
       //A local constants 
       
       final   
       
       String 
       
       Name 
       
       =
       
       "磊哥java历险记";
       
       //打印 
       
       System.
       
       out.
       
       println(
       
       Name);
       
       System.
       
       out.
       
       println(
       
       name);
       
    }
       
}
      
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Do you remember how many constants and the data type？_数据类型_13

代码总结

You can try typing the following code,Advice for beginners,切勿直接复制粘贴,This is fake learning,It takes time to gain,Don't waste your study time,Since time and experience,Then you must gain,Get it done, brothers！！！.

       
       package 
       
       com.
       
       Test;
       
       /*
       
       常量:固定不变的数
       
       整数,小数,字符,布尔,字符串
       
       磊哥的java历险记@51博客
       
       */
       
       public 
       
       class 
       
       Main{
       
       // 静态常量
       
       public 
       
       static 
       
       final 
       
       String 
       
       name 
       
       = 
       
       "磊哥java历险记";
       
       // 声明成员常量
       
       final 
       
       int 
       
       y 
       
       = 
       
       10;
       
       public 
       
       static 
       
       void 
       
       main(
       
       String[] 
       
       args){
       
       //整数
       
       //十进制:常用
       
       System.
       
       out.
       
       println(
       
       8);
       
       //二进制:以0b/0B开头 只包含0和1
       
       System.
       
       out.
       
       println(
       
       0b1000);
       
       //十六进制:以0x/0X开头 0-9 a-f
       
       System.
       
       out.
       
       println(
       
       0x8);
       
       System.
       
       out.
       
       println(
       
       0xb);
       
       //八进制:以0开头 0-7
       
       System.
       
       out.
       
       println(
       
       010);
       
       //8
       
       System.
       
       out.
       
       println(
       
       011);
       
       //9
       
       System.
       
       out.
       
       println(
       
       017);
       
       //15
       
       //小数
       
       System.
       
       out.
       
       println(
       
       3.1415926);
       
       //布尔
       
       System.
       
       out.
       
       println(
       
       true);
       
       System.
       
       out.
       
       println(
       
       false);
       
       //字符 必须用''包裹起来 不能为空
       
       System.
       
       out.
       
       println(
       
       '1');
       
       System.
       
       out.
       
       println(
       
       'a');
       
       System.
       
       out.
       
       println(
       
       'B');
       
       //System.out.println('磊哥');
       
       System.
       
       out.
       
       println(
       
       '&');
       
       System.
       
       out.
       
       println(
       
       ' ');
       
       //System.out.println('10');//错误: 未结束的字符文字
       
       //字符串 必须用""包裹起来
       
       System.
       
       out.
       
       println(
       
       "磊哥的java历险记@51博客!");
       
       System.
       
       out.
       
       println(
       
       "");
       
       //定义一个name常量
       
       final   
       
       String 
       
       Name 
       
       =
       
       "/磊哥的java历险记@51博客";
       
       //打印
       
       System.
       
       out.
       
       println(
       
       Name);
       
       System.
       
       out.
       
       println(
       
       name);
       
    }
       
}
      
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结语

This article introduces you to constants and data types,beginner brothers,Can be practical,In the middle of the case,try to do it yourself,The code must be typed by yourself to be rewarded.

Do you remember how many constants and the data type？_java_14