(1)HelloWorld
//单行注释:类名规范:1.大写驼峰 2.见名知意 3.类名必须与java文件名一致
public class HelloWorld{
//程序的入口(函数/方法/功能)
public static void main(String[] args){
System.out.println(100);
System.out.println("Hello world");
}
}
//compiler编译 comment注释 font字体 author作者 descrption描述 version版本
live templates 动态模板
直接Sop即可。
(2)
/** * @author: sunshine * @description: 维护学生的基本信息 * @data: 2022/2/9 19:38 * @version: 0.1 * @since: jdk11 */ public class studentinfo { public static void main(String[] args){ char gender = '男'; String studentName = "李四"; int studentNo = 20; byte age = 28; float score = 100; boolean flag = true; System.out.println(gender); System.out.println(studentName); System.out.println(studentNo); System.out.println(age); System.out.println(score); System.out.println(flag); } }
//ctrl+d向下复制 ctrl+y单行删除
(3)
/** * @author: sunshine * @description:描述手机信息 * @data: 2022/2/9 20:00 * @version: 0.1 * @since: jdk11 */ public class phoneInfo { public static void main(String[] args){ String brand = "小米"; double weight = 12.4; int capacity = 4050; int price = 6999; double thickness = 5.3; System.out.println(brand); System.out.println(weight); System.out.println(capacity); System.out.println(price); System.out.println(thickness); } }
(4)
/** * @author: sunshine * @description: 使用局部变量定义所有的数据类型 * @data: 2022/2/9 20:17 * @version: 0.1 * @since: jdk11 */ public class DataType { public static void main(String[] args){ //整数类型 byte by = -100; short sh = 100; int num = 1000; long longNum = 100L; //小数类型 float f = 10.0F; double d = 10.1111; //单字符类型 char c1 = 'a'; char c2 = '1'; char c3 = '我'; char c4 = 97;//ASCII char c5 = '\u67d0'; System.out.println(c1); System.out.println(c2); System.out.println(c3); System.out.println(c4); System.out.println(c5); //布尔类型 boolean flag = true; System.out.println(flag); //引用类型 String str = "hello"; String str1 = new String("hello");//括号里是“hello” System.out.println(str); System.out.println(str1); } }
(5)
/** * @author: sunshine * @description: 数据类型转换 * @data: 2022/2/9 20:44 * @version: 0.1 * @since: jdk11 */ public class DatatypeConverter { public static void main(String[] args){ //自动转换 int num = 100; double douNum = num; System.out.println(douNum); char ch = 'a';//97 int num1 = ch; System.out.println(num1); //强制类型转换 double dou = 10.45678; int n = (int)dou;//变量=(目标类型)原类型 System.out.println(n); byte b = (byte) n;//alt+回车 System.out.println(b); short s1 = 10; short s2 = 10; short num3 = (short)(s1 + s2); System.out.println(num3); } }
(6)
/** * @author: sunshine * @description: 运算符 * @data: 2022/2/9 20:57 * @version: 0.1 * @since: jdk11 */ public class Yunsuanfu { public static void main(String[] args){ //赋值运算符 算术运算符 int num1 = 100; int num2 = 10; System.out.println(num1 + num2);//110 System.out.println(num1 - num2);//90 System.out.println(num1 * num2);//1000 System.out.println(num1 / num2);//10 System.out.println(num1 % num2);//0 int num3 = 10; num3 += 10;//num3 = num3 +10;//20 num3 -= 10;//10 num3 /= 10;//1 num3 *= 10;//10 num3 %= 3;//1 System.out.println(num3); //++ -- int a = 10; int b = a++;//先将a的数值赋值给b,a再自增加1 System.out.println(b);//b=10 System.out.println(a);//a=11 b = ++a;//a先自增加1,再将自增后的结果赋值给b System.out.println(b);//b=12 System.out.println(a);//a=12 int x = 100; x = ++x;//x自增加1,再赋值给,故x=101 System.out.println(x); x = x++;//x直接赋值给x,故x=101.实际为:temp = x;x++;x = temp;(用到变量缓存) System.out.println(x); String name = "张三"; int age = 30; System.out.println("用户名"+name); System.out.println("年龄"+age); } }
(7)
/** * @author: sunshine * @description: 比较运算符 * @data: 2022/2/9 21:20 * @version: 0.1 * @since: jdk11 */ public class Yunsuanfu1 { public static void main(String[] args){ //基本数据类型比较的是数据 占一块栈内存 //局部变量 int num1 = 100; int num2 = 200; System.out.println(num1 > num2);//false System.out.println(num1 >= num2);//false System.out.println(num1 < num2);//true System.out.println(num1 <= num2);//true //引用数据类型比较的是内存地址值 占据两块堆内存 //变量和引用是一个概念,变量名称全部在队内存 //对String而言,数据是常量,在常量池(gdk1.8之后) String str1 = "hello"; String str2 = "hello"; String str3 = new String("hello"); System.out.println(str1); System.out.println(str2); System.out.println(str3); System.out.println(str1==str2);//true System.out.println(str1==str3);//false //比较用户名或者密码 比较字符串数据 字符串1.equals(字符串2) System.out.println(str1.equals(str3));//true } }
(8)
/** * @author: sunshine * @description: 逻辑运算符 * @data: 2022/2/9 21:39 * @version: 0.1 * @since: jdk11 */ public class Yunsuanfu2 { public static void main(String[] args){ //逻辑运算符:多个表达式之间运算 //用户登录:用户名和密码一致 String trueName = "admin"; String truePass = "1234"; boolean flag1 = "admin".equals(trueName); boolean flag2 = "123".equals(truePass); System.out.println(flag1 && flag2); int num1 = 10; int num2 = 100; //第一个表达式true 不管使用&/&& 后面的表达式都要参与运算 System.out.println((num1 < num2) & (num1 > num2)); System.out.println((num1 < num2) && (num1 > num2)); //第一个表达式false,&&后面就没必要执行,而&还要执行 //&&:短路与 推荐使用 //&:表达式全部都要执行 System.out.println((num1 > num2) && (num1 < num2)); System.out.println((num1 > num2) && (num1 < num2)); //同上 System.out.println((num1 > num2) | (num1 < num2)); System.out.println((num1 > num2) || (num1 < num2)); //^异或,相同则为false System.out.println(false ^ true); //! 非,相反的结果 System.out.println(!true); } }
(9)
/** * @author: sunshine * @description: 位运算 * @data: 2022/2/9 22:00 * @version: 0.1 * @since: jdk11 */ public class Yunsuanfu3 { public static void main(String[] args){ System.out.println(4 & 7);//转换成2进制进行位运算,结果为4 //0100 //0111 //0100 System.out.println(4 | 7);//7 System.out.println(4 ^ 7);//0011,结果为3 }
(10)
/** * @author: sunshine * @description: 三元运算符 * @data: 2022/2/9 22:05 * @version: 0.1 * @since: jdk11 */ public class Yunsuanfu4 { public static void main(String[] args){ String result = (4 > 7)?"hello":"helloWorld";//helloWorld System.out.println(result); //看精度高的数据类型 int num = (int)((5 < 1)?100:200.234);//200 System.out.println(num); //求三个数的最值 int a = 100,b = 200,c = 300; int max = (a > b)?a:b; max = (max > c)?max:c; //或者int max = (a > b)?((a > c)?a:c):((b > c)?b:c); System.out.println(max); } }