03Java运算表达式,格式化

小咪咪 2024-03-27 11:01 30阅读 0赞

> **运算符：是一种特殊符号，用以表示数据的运算、赋值和比较。**
> 
> **表达式：使用运算符将运算数据连接起来的符合Java语法规则的式子。**

## 一、运算表达式 ##

### 1.算术运算符 ###

**+ - \* / 整除求整商 % 求余数 ++ -- 运算**

/*
 * Copyright (c) 2020, 2023, 3044483124@qq.com All rights reserved.
 *
 */
 package itcast;
 
 /**
 * Project: JavaStudy - Opt1
 * Powered by jiangbo On 2023-01-31
 * 14:45:09
 * Created by IntelliJ IDEA
 *
 * @author jiangbo [3044483124@qq.com]
 * @version 1.0
 * @since 8/17
 */
 public class Opt1 {
 public static void main(String[] args) {
 int a = 10;
 int b = 2;
 System.out.printf("%d + %d = %d%n", a, b, a + b);
 System.out.printf("%d - %d = %d%n", a, b, a - b);
 System.out.printf("%d × %d = %d%n", a, b, a * b);
 //求整商
 System.out.printf("%d ÷ %d = %d%n", a, b, a / b);
 //求余数
 System.out.printf("%d %% %d = %d%n", a, b, a % b);
 int c = 5;
 //变量自身值加1
 ++c;
 System.out.println(c);
 //d = 6,c = 7
 
 int d = c++;
 //int d = ++c;
 System.out.println(c);
 System.out.println(d);
 d--;
 System.out.println(d);
 System.out.println(--d);
 }
 }

### ![2b2f00cceb034baebfd283ce72869b08.png][] ###

### 2.赋值运算符 ###

**= += -= \*= /= %=** (java 程序中 = 赋值 == 判断是不是同一个对象)

/*
 * Copyright (c) 2020, 2023, 3044483124@qq.com All rights reserved.
 *
 */
 package itcast;
 
 /**
 * Project: JavaStudy - Opt2
 * Powered by jiangbo On 2023-01-31
 * 15:39:44
 * Created by IntelliJ IDEA
 *
 * @author jiangbo [3044483124@qq.com]
 * @version 1.0
 * @since 8/17
 */
 public class Opt2 {
 public static void main(String[] args) {
 int a = 10, b = 3;
 int c = 2;
 c += a * b;
 System.out.println(c);
 c = c + a * b;
 System.out.println(c);
 //50
 System.out.println(c-=12);
 System.out.println(c*=2);
 System.out.println(c/=25);
 System.out.println(c%=3);
 //java 程序中 = 赋值 == 判断是不是同一个对象
 }
 }

### ![43e43334eb3c4abaa8dc8e51dfca026f.png][] ###

### 3.比较运算 ###

**> >= < <= == != instanceof**

比较运算 > >= < <= != == instanceof 判断对象不是是某类的实例

/*
 * Copyright (c) 2020, 2023, 3044483124@qq.com All rights reserved.
 *
 */
 package itcast;
 
 /**
 * Project: JavaStudy - Opt3
 * Powered by jiangbo On 2023-01-31
 * 15:52:22
 * Created by IntelliJ IDEA
 *
 * @author jiangbo [3044483124@qq.com]
 * @version 1.0
 * @since 8/17
 */
 public class Opt3 {
 public static void main(String[] args) {
 //比较运算 > >= < <= != <> == instanceof 判断对象不是是某类的实例
 //false
 System.out.println(2>3);
 //false
 System.out.println(2>=3);
 //false
 System.out.println(2==3);
 //true
 System.out.println(2<3);
 //true
 System.out.println(2<=3);
 //true
 System.out.println(2!=3);
 String s1 = "李四";
 String s2 = "王五";
 //false
 System.out.println(s1==s2);
 //true
 System.out.println(s1 instanceof String);
 }
 
 }

![a3e4a747b11748ffa6e5388a12e503d2.png][]

### 4.逻辑运算符 ###

**逻辑运算 与 "&&","&" 或"||","| "非 "!" 异或 "^"(&& 支持短路效率高 & 不支持短路效率低)**

/*
 * Copyright (c) 2020, 2023, 3044483124@qq.com All rights reserved.
 *
 */
 package itcast;
 
 /**
 * Project: JavaStudy - Opt4
 * Powered by jiangbo On 2023-01-31
 * 16:00:49
 * Created by IntelliJ IDEA
 *
 * @author jiangbo [3044483124@qq.com]
 * @version 1.0
 * @since 8/17
 */
 public class Opt4 {
 public static void main(String[] args) {
 //逻辑运算 与 && & 或 || | 非 ! 异或 ^
 //true && 支持短路效率高 & 不支持短路效率低
 System.out.println(true && true);
 System.out.println(true & true);
 //false
 System.out.println(true && false);
 System.out.println(true & false);
 System.out.println(false && true);
 System.out.println(false & true);
 System.out.println(false && false);
 System.out.println(false & false);
 System.out.println("-".repeat(30));
 int a = 1;
 int b = 2;
 //&&支持短路 false 1 2
 boolean f = a==2 && ++b == 2;
 //&不支持短路 false 1 3
 //boolean f = a==2 & ++b == 2;
 System.out.println(f);
 System.out.println(a);
 System.out.println(b);
 System.out.println("*".repeat(35));
 //|| 逻辑或 |
 System.out.println(true||true);
 System.out.println(true||false);
 System.out.println(false||true);
 System.out.println(false||false);
 System.out.println("*".repeat(35));
 //^ 逻辑异或
 System.out.println(true^true);
 System.out.println(true^false);
 System.out.println(false^true);
 System.out.println(false^false);
 //逻辑非 ！
 System.out.println("*".repeat(35));
 System.out.println(!!false && !(3==2));
 System.out.println(!false && !(3==2));
 System.out.println(true && true);
 }
 
 }

## ![2b2d14a394934ebcb5dcfd58e5daae3d.png][] ##

![138d8c36d55c4dd4a54307c913c86872.png][]

**小案例：分时问候。**

/*
 * Copyright (c) 2020, 2023, 3044483124@qq.com All rights reserved.
 *
 */
 package itcast;
 
 import java.time.LocalTime;
 
 /**
 * Project: JavaStudy - Ex1
 * Powered by jiangbo On 2023-01-31
 * 16:27:36
 * Created by IntelliJ IDEA
 *
 * @author jiangbo [3044483124@qq.com]
 * @version 1.0
 * @since 8/17
 */
 public class Ex1 {
 public static void main(String[] args) {
 //idea ctrl + d 复制一行
 //idea shift + alt + up|down
 //时间类、if分支语句
 var now = LocalTime.now();
 //早上好 6-8 上午好 8-12 12-14 14-18 18-20 20-23
 int hour = now.getHour();
 if (hour >= 6 && hour < 8) {
 System.out.println("早上好");
 } else if (hour >= 8 && hour < 12) {
 System.out.println("上午好");
 } else if (hour >= 12 && hour < 14) {
 System.out.println("中午好");
 } else if (hour >= 14 && hour < 18) {
 System.out.println("下午好");
 } else if (hour >= 18 && hour < 21) {
 System.out.println("晚上好");
 }
 }
 }

### 5.位运算符 ###

~ & | >> <<

位运算是直接对整型数据的二进制进行运算。

**1.按位与（&）**  
将参加运算的两个数据，按二进制位进行"与"运算。两个都是一则为一

举例: 3 & 5

3 => 0000 0000 0000 0011

5 => 0000 0000 0000 0101

& 0000 0000 0000 0001 转换成十进制也就是1

**2.按位或（|）**  
将参加运算的两个数据，按二进制位进行"或"运算。两个中有一个是一则为一

举例: 3 | 5

3 => 0000 0000 0000 0011

5 => 0000 0000 0000 0101

| 0000 0000 0000 0111 转换成十进制也就是7

**3.按位取反（~）**  
将数据，按二进制位进行"取反"运算。零变成一，一变成零

举例: ~6

6 => 0000 0000 0000 0110

~ 1111 1111 1111 1010 转换成十进制也就是-7

**4.异或（^）**  
将参加运算的两个数据，按二进制位进行"与"运算。相同为零，不同为一

举例: 3 ^ 5

3 => 0000 0000 0000 0011

5 => 0000 0000 0000 0101

^ 0000 0000 0000 0110 转换成十进制也就是6

运算法则:

n ^ 0 = n  
n ^ n = 0  
a ^ b = b ^ a  
a ^ b ^ c = a ^ (b ^ c) = (a ^ b) ^ c;  
d = a ^ b ^ c a ^ b ^ a = b. 可以推出 a = d ^ b ^ c.

**5.同或（~）**  
将参加运算的两个数据，按二进制位进行"同或"运算。相同为一，不同为零

举例: 3 同或 5

3 => 0000 0000 0000 0011

5 => 0000 0000 0000 0101

1111 1111 1111 0001 转换成十进制也就是-7

java语言中只有异或(^)没有同或符号

但是可以用代码实现 A 同或 B = (A ^ B)再按位取反

public static int sameOr(int a, int b) \{ 
return ~(a ^ b); 
\} 
**6.左移（<<）** 
<< ： 在一定范围内，每向左移 1 位，就相当于 \* 2；

举例: 3 << 5

3 => 0000 0000 0000 0011

<< 0000 0000 0110 0000 转换成十进制也就是 96 = 3 \* (2^5) (这里的^代表几次方 不是异或)

面试题：最高效的计算 2 \* 8？

2 << 3 / 8 << 1

**7.右移（>>）**  
>> : 在一定范围内，每向右移 1 位，就相当于 / 2；

举例: 96 >> 5

96 => 0000 0000 0110 0000

<< 0000 0000 0000 0011 转换成十进制也就是 3 = 96 / (2^5)

## 二、格式化 ##

### 1.格式日期时间 ###

### ![d1f136bb721140849d2bd7e79f46e569.png][]2.格式化数字 ###

/*
 * Copyright (c) 2020, 2023, 3044483124@qq.com All rights reserved.
 *
 */
 package itcast;
 
 import java.text.NumberFormat;
 import java.util.Locale;
 
 /**
 * Project: JavaStudy - Formatnumber
 * Powered by jiangbo On 2023-01-31
 * 21:49:42
 * Created by IntelliJ IDEA
 *
 * @author jiangbo [3044483124@qq.com]
 * @version 1.0
 * @since 8/17
 */
 public class Formatnumber {
 public static void main(String[] args) {
 int a = 1424248;
 float b = .5F;
 int c = 3;
 System.out.printf("%03d %d %.3f%n", c, a, b);
 //格式化货币
 NumberFormat nf1 = NumberFormat.getCurrencyInstance();
 nf1.setMinimumFractionDigits(5);
 
 System.out.println(nf1.format(a));
 NumberFormat nf2 = NumberFormat.getCurrencyInstance(Locale.US);
 System.out.println(nf2.format(a));
 }
 
 }

![eb3e9b1b477b4a93b932fa0b9cff9b0b.png][]

### **3.格式化字符串** ###

/*
 * Copyright (c) 2020, 2023, 3044483124@qq.com All rights reserved.
 *
 */
 package itcast;
 
 /**
 * Project: JavaStudy - FormatString
 * Powered by jiangbo On 2023-01-31
 * 21:53:23
 * Created by IntelliJ IDEA
 *
 * @author jiangbo [3044483124@qq.com]
 * @version 1.0
 * @since 8/17
 */
 public class FormatString {
 public static void main(String[] args) {
 int id = 3;
 String name = "李四";
 int age = 18;
 String address = "河南省郑州市";
 System.out.printf("编号：%03d，姓名：%s，年龄：%d岁，家庭地址：%s。", id,
 name, age, address);
 //格式化字符串 左对齐 右对齐 大写显示 小写显示
 System.out.printf("%n");
 System.out.printf("%-10s%-6d%n","张三",18);
 System.out.printf("%-10s%-6d%n","张三丰",9);
 System.out.printf("%S %<s%n","helloworld");
 }
 }

[2b2f00cceb034baebfd283ce72869b08.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/27/e034ad6860504884b0625e834594e351.png
[43e43334eb3c4abaa8dc8e51dfca026f.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/27/fe34ab388e33479b8262666c6ca7146d.png
[a3e4a747b11748ffa6e5388a12e503d2.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/27/fe41ca1b55f949589f2018c20f3f7bd3.png
[2b2d14a394934ebcb5dcfd58e5daae3d.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/27/0f282f89bbca4d82a14d667e67b63d18.png
[138d8c36d55c4dd4a54307c913c86872.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/27/f63f60d588a54a80b4b8b9143f81dbe8.png
[d1f136bb721140849d2bd7e79f46e569.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/27/96ed61d27da343dbb07de0ef6347af33.png
[eb3e9b1b477b4a93b932fa0b9cff9b0b.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/27/ddca46e7c98e4cc8a0a7c756cfde05a7.png