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基础语法学习

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刘引
2023-07-26 17:37:12 +08:00
parent 49d62740e8
commit 71d47398ae
36 changed files with 445 additions and 17 deletions
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.idea/misc.xml generated
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<?xml version="1.0" encoding="UTF-8"?>
<project version="4">
<component name="ProjectRootManager" version="2" languageLevel="JDK_20" project-jdk-name="zulu-1.8" project-jdk-type="JavaSDK">
<component name="ProjectRootManager" version="2" languageLevel="JDK_1_8" default="true" project-jdk-name="zulu-1.8" project-jdk-type="JavaSDK">
<output url="file://$PROJECT_DIR$/out" />
</component>
</project>

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<project version="4">
<component name="ProjectModuleManager">
<modules>
<module fileurl="file://$PROJECT_DIR$/Hello/Hello.iml" filepath="$PROJECT_DIR$/Hello/Hello.iml" />
<module fileurl="file://$PROJECT_DIR$/JavaSE/JavaSE.iml" filepath="$PROJECT_DIR$/JavaSE/JavaSE.iml" />
<module fileurl="file://$PROJECT_DIR$/.idea/java学习.iml" filepath="$PROJECT_DIR$/.idea/java学习.iml" />
<module fileurl="file://$PROJECT_DIR$/基础语法/基础语法.iml" filepath="$PROJECT_DIR$/基础语法/基础语法.iml" />
</modules>
</component>
</project>

0
Hello/.idea/uiDesigner.xml → .idea/uiDesigner.xml generated
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10
Hello/src/src/Hello.java
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@@ -1,10 +0,0 @@
public class Hello {
public static void main(String[] args) {
System.out.println("主方法");
test("传值");
}
public static void test(String S) {
System.out.println(S);
}
}

5
Hello/src/src/Main.java
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public class Main {
public static void main(String[] args) {
System.out.println("Hello world!");
}
}

0
Hello/.idea/.gitignore → 基础语法/.idea/.gitignore generated vendored
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Hello/.idea/misc.xml → 基础语法/.idea/misc.xml generated
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Hello/.idea/modules.xml → 基础语法/.idea/modules.xml generated
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Hello/out/production/code/.idea/uiDesigner.xml → 基础语法/.idea/uiDesigner.xml generated
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Hello/out/production/code/.idea/.gitignore → 基础语法/out/production/code/.idea/.gitignore generated vendored
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Hello/out/production/code/.idea/code.iml → 基础语法/out/production/code/.idea/code.iml generated
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Hello/out/production/code/.idea/misc.xml → 基础语法/out/production/code/.idea/misc.xml generated
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<property name="text" value="Button" />
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Hello/out/production/src/Hello.class → 基础语法/out/production/src/Hello.class
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0
Hello/src/.gitignore → 基础语法/src/.gitignore vendored
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基础语法/src/src/com/kuang/base/Demo02.java Normal file
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package com.kuang.base;
public class Demo02 {
public static void main(String[] args) {
// 八大基本数据类型
// 整数
int num1 = 10;//最常用
byte num2 = 20;
short num3 = 30;
long num4 = 1000;//Long类型要在数字后面加个L
// 小数：浮点数
float num5 = 50.1F;//float后面需要加F
double num6 = 3.1415926;
// 字符类型
char name = 'A';
// 字符串类型，string不是关键字，类
String name1 = "测试";
boolean flag = true;
}
}

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基础语法/src/src/com/kuang/base/Demo03.java Normal file
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package com.kuang.base;
public class Demo03 {
public static void main(String[] args) {
// 整数扩展: 进制 二进制0b 十进制 八进制0 十六进制0x
int i = 10;
int i2 = 010;//八进制
int i3 = 0x10;//十六进制
System.out.println(i);
System.out.println(i2);
System.out.println(i3);
// ================================
// 浮点数扩展： 银行业务怎么表示
// BigDecimal 数学工具类
System.out.println(0.1 + 0.2);//0.30000000000000004
System.out.println(0.1f + 0.2f);//0.3
// ================================
// float 有限 离散 舍入误差 大约 接近但不等于
// double
// 最好完全避免使用浮点数进行比较
float f = 0.1f;
double d = 1.0 / 10;
System.out.println(f == d);//false
// ==================================
// 字符扩展
// ==================================
char c1 = 'a';
char c2 = '中';
System.out.println(c1);
System.out.println((int) c1);//强制转换
System.out.println(c2);
System.out.println((int) c2);//强制转换
// 所有的字符本质还是数字
// 编码 Unicode 表：97=a 65=A 48=0
// U0000 UFFFF
// ==================================
// 转义字符
// ==================================
System.out.println("Hello\nWorld");//换行
System.out.println("Hello\tWorld");//制表符
System.out.println("Helloooo\tWorld");//制表符
System.out.println("Hello\rWorld");//回车
System.out.println("Hello\bWorld");//退格
System.out.println("Hello\"World\"");//双引号
System.out.println("Hello\'World\'");//单引号
String sa = new String("Hello");
String sb = new String("Hello");
System.out.println(sa == sb);//false
String sc = "Hello";
String sd = "Hello";
System.out.println(sc == sd);//true
// ==================================
// 布尔值扩展
// ==================================
boolean flag = true;
if (flag) {
System.out.println("真");
} else {
System.out.println("假");
}
}
}

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基础语法/src/src/com/kuang/base/Demo04.java Normal file
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package com.kuang.base;
public class Demo04 {
public static void main(String[] args) {
int i = 128;
byte b = (byte) i;//内存溢出
// 强制转换(类型)变量名 高->低
// 自动转换 低->高
System.out.println(i);
System.out.println(b);
/*
注意点：
1.不能对布尔值进行转换
2.不能把对象类型转换为不相干的类型
3.把高容量转换到低容量的时候，强制转换
4.转换的时候可能存在内存溢出，或者精度问题！
*/
System.out.println((int) 23.7);//23
char c = 'a';
int d = c + 1;
System.out.println(d);//98
System.out.println((char) d);//b
}
}

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基础语法/src/src/com/kuang/base/Demo06.java Normal file
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package com.kuang.base;
public class Demo06 {
public static void main(String[] args) {
// 操作比较大的数的时候，注意溢出问题
// jdk7新特性，数字之间可以用下划线分割
int money = 10_0000_0000;
int years = 20;
int total = money * years;//-1474836480
long total1 = money * years;//默认是int类型，转换之前已经存在问题了
long total2 = money * (long) years;//先把一个因子变成long类型，整个表达式发生提升
System.out.println(total);//-1474836480
long tatal3 = money * ((long) years);
System.out.println(tatal3);//20000000000
}
}

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基础语法/src/src/com/kuang/base/Demo07.java Normal file
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package com.kuang.base;
public class Demo07 {
public static void main(String[] args) {
int a = 1, b = 2, c = 3, d = 4;
String name = "qinjiang";
char x = 'X';
double pi = 3.14;
}
}

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基础语法/src/src/com/kuang/base/Demo08.java Normal file
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package com.kuang.base;
public class Demo08 {
// 属性：变量
// 实例变量：从属于对象；如果不进行初始化，会有一个默认值 0 0.0 null
// 布尔值：默认是false
// 除了基本类型，其余的默认都是null
String name;
int age;
static double salary = 2500;
// main方法
public static void main(String[] args) {
// 局部变量；必须声明和初始化值
int i = 10;
System.out.println(i);
Demo08 demo08 = new Demo08();
System.out.println(demo08.age);
System.out.println(salary);
// 类变量：static
}
// 其他方法
public void add() {
}
}

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基础语法/src/src/com/kuang/base/Demo09.java Normal file
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package com.kuang.base;
public class Demo09 {
// 修饰符不存在先后顺序
final static double PI = 3.14;
public static Number main(String[] args) {
System.out.println(PI);
return PI;
}
}

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基础语法/src/src/com/kuang/opertate/Demo01.java Normal file
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package com.kuang.opertate;
public class Demo01 {
public static void main(String[] args) {
// 二元运算符
int a = 10;
int b = 20;
int c = 30;
int d = 40;
System.out.println(a + b);//30
System.out.println(a - b);//-10
System.out.println(a * b);//200
System.out.println(a / (double) b);//0
}
}

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基础语法/src/src/com/kuang/opertate/Demo02.java Normal file
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package com.kuang.opertate;
public class Demo02 {
public static void main(String[] args) {
long a = 123123123123L;
int b = 123;
short c = 10;
byte d = 8;
System.out.println(a + b + c + d);
int e = (int) a;
System.out.println(e);
}
}

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基础语法/src/src/com/kuang/opertate/Demo03.java Normal file
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package com.kuang.opertate;
public class Demo03 {
public static void main(String[] args) {
// 关系运算符返回的结果
int flag = test(null);
System.out.println(flag);
}
public static int test(String[] args) {
int a = 10;
int b = 20;
return a + b;
/* System.out.println(a > b);
System.out.println(a < b);
System.out.println(a == b);
System.out.println(a != b);*/
}
}

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基础语法/src/src/com/kuang/opertate/Demo04.java Normal file
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package com.kuang.opertate;
public class Demo04 {
public static void main(String[] args) {
int a = 3;
int b = a++;//先赋值后自增
int c = ++a;//先自增后赋值
System.out.println(a);
System.out.println(b);
System.out.println(c);
// 幂运算 2^3 很多运算 我们会使用一些工具类来操作
double pow = Math.pow(2, 3);
System.out.println(pow);
}
}

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基础语法/src/src/com/kuang/opertate/Demo05.java Normal file
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package com.kuang.opertate;
//逻辑运算符
public class Demo05 {
public static void main(String[] args) {
// 与 或 非
int a = 10;
int b = 20;
int c = 30;
int d = 40;
System.out.println(a > b && c > d);//false
System.out.println(a > b || c > d);//false
System.out.println(!(a > b));//true
// 短路运算
int e = 5;
boolean f = (e < 4) && (e++ < 4);
System.out.println(f);//false
System.out.println(e);//5
}
}

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基础语法/src/src/com/kuang/opertate/Demo06.java Normal file
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package com.kuang.opertate;
public class Demo06 {
public static void main(String[] args) {
/*
* A=0011 1100
* B=0000 1101
* A&B=0000 1100
* A|B=0011 1101
* A^B=0011 0001
* ~B=1111 0010
* 2*8=16 2*2*2*2=16
* 效率极高
* << *2
* >> /2
*
* */
System.out.println(2 << 3);//16
}
}

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基础语法/src/src/com/kuang/opertate/Demo07.java Normal file
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package com.kuang.opertate;
public class Demo07 {
public static void main(String[] args) {
int a = 10;
int b = 20;
a += b;//a=a+b
a -= b;//a=a-b
System.out.println(a);
// 字符串连接符
System.out.println(a + b);
// 字符串连接符
System.out.println("" + a + b);
System.out.println(a + b + "");
}
}

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基础语法/src/src/com/kuang/opertate/Demo08.java Normal file
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package com.kuang.opertate;
import com.kuang.base.Demo09;
public class Demo08 {
public static void main(String[] args) {
// x?y:z
// 如果x==true，则结果为y，否则结果为z
int score = 80;
String type = score < 60 ? "不及格" : "及格";
// System.out.println(type);
Demo09 demo09 = new Demo09();
demo09.main(null);
}
}

0
Hello/Hello.iml → 基础语法/基础语法.iml
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