• 学习自B站：【狂神说Java】Java零基础学习视频通俗易懂

• Java基础（流程控制）

package com.HJX.scanner;​import java.util.Scanner;​public class Demo01 {​public static void main(String[] args) {​//创建一扫描器对象，用于接受键盘数据Scanner scanner = new Scanner(System.in);​System.out.println("使用next方式接收：");​//判断用户有没有输入字符串if (scanner.hasNext()){//接收用户的输入String str = scanner.next();//程序会等待用户输入完毕System.out.println("输入的内容为："+str);}//凡是属于IO流的类如果不关闭就会一直占用资源，要养成好习惯用掉就关闭scanner.close();}}

package com.HJX.scanner;​import java.util.Scanner;​public class Demo02 {​public static void main(String[] args) {​Scanner scanner = new Scanner(System.in);​System.out.println("使用nextLine方式接收：");​if (scanner.hasNextLine()){String str = scanner.nextLine();System.out.println("输入的内容为："+str);}​scanner.close();​     }}

 package com.HJX.scanner;​import java.util.Scanner;​public class Demo03 {​public static void main(String[] args) {​Scanner scanner = new Scanner(System.in);​System.out.println("请输入数据：");​String str = scanner.nextLine();​System.out.println("输入的内容为："+str);​scanner.close();}}

package com.HJX.scanner;​import java.util.Scanner;​public class Demo04 {​public static void main(String[] args) {​Scanner scanner = new Scanner(System.in);​//从键盘接收数据int i = 0;float f = 0.0f;​System.out.println("请输入整数:");​if (scanner.hasNextInt()){i = scanner.nextInt();System.out.println("整数数据"+i);}else {System.out.println("输入的不是整数数据!");}​System.out.println("请输入小数:");​if (scanner.hasNextFloat()){f = scanner.nextFloat();System.out.println("小数数据"+f);}else {System.out.println("输入的不是小数数据!");}scanner.close();}}

package com.HJX.scanner;​import java.util.Scanner;​public class Demo05 {​public static void main(String[] args) {//我们可以输入多个数字,并求其总和与平均数,每输入一个数字用回车确认,通过输入非数字来结束输入,并输出执行结果​Scanner scanner = new Scanner(System.in);​//Sumdouble sum = 0;//计算输入了多少个数字int m = 0;​System.out.println("请输入数据：");//通过循环判断是否还有输入，并在其中对每一次进行求和统计while (scanner.hasNextDouble()){double x = scanner.nextDouble();m = m + 1;sum = sum + x;System.out.println("你输入了第"+m+"个数据,当前的结果Sum为："+sum);}​System.out.println(m+"个数的和为："+sum);System.out.println(m+"个数的平均数为："+(sum/m));​scanner.close();}}

顺序结构

package com.HJX.Struct;​public class sequence_Demo01 {​public static void main(String[] args) {​System.out.println("hello1");System.out.println("hello2");System.out.println("hello3");System.out.println("hello4");System.out.println("hello5");}}

选择结构

• if单选择结构

• if双选择结构

• if多选择结构

• 嵌套的if结构

• switch多选择结构

package com.HJX.Struct;​import java.util.Scanner;​public class if_Demo01 {​public static void main(String[] args) {​Scanner scanner = new Scanner(System.in);​System.out.println("请输入内容:");String s = scanner.nextLine();​//equals的作用为判断字符串是否相等if (s.equals("Hello")){System.out.println(s);}​System.out.println("End");​scanner.close();}}

package com.HJX.Struct;​import java.util.Scanner;​public class if_Demo03 {​public static void main(String[] args) {​Scanner scanner = new Scanner(System.in);​System.out.println("请输入成绩:");int score = scanner.nextInt();​if (score==100){System.out.println("满分");}else if (90<=score && score<100){System.out.println("优秀");}else if (70<=score && score<90){System.out.println("良好");}else if (60<=score && score<70){System.out.println("及格");}else {System.out.println("成绩不合法");}​scanner.close();}}

package com.HJX.Struct;public class Switch_Demo01 {public static void main(String[] args) {//case穿透-----与break有关//switch 匹配一个具体的值char grade = 'C';switch (grade){case 'A':System.out.println("优秀");break;case 'B':System.out.println("良好");break;case 'C':System.out.println("及格");break;case 'D':System.out.println("不及格");break;default:System.out.println("未知等级");}}
}

package com.HJX.Struct;public class Switch_Demo02 {public static void main(String[] args) {String name = "计算机";//JDK7新特性,表达式结果可以是字符串//字符的本质还是数字switch (name){case "机械":System.out.println("机械");break;case "计算机":System.out.println("计算机");break;case "电子信息":System.out.println("电子信息");break;default:System.out.println("无专业匹配");}}
}

循环结构

• while循环

• do...while循环

• for循环

• 在Java5中引入了一种主要用于数组的增强型for循环

package com.HJX.Struct;public class While_Demo01 {public static void main(String[] args) {//输出1~100int i = 0;while (i<100){i = i + 1; //i++System.out.println(i);}}
}

package com.HJX.Struct;public class While_Demo02 {public static void main(String[] args) {//计算1+2+...+100int i = 1;int sum = 0;while (i<=100){sum = sum + i;i++; //i = i + 1}System.out.println(sum);}
}

package com.HJX.Struct;public class DoWhile_Demo02 {public static void main(String[] args) {int a = 0;while (a<0){System.out.println(a);a++;}System.out.println("-----------------------");do {System.out.println(a);a++;}while (a<0);      }
}

package com.HJX.Struct;public class For_Demo01 {public static void main(String[] args) {int a = 1;//初始化条件while (a<=100){//判断条件System.out.println(a);//循环体a = a + 1;//迭代}System.out.println("while循环结束");for (int i=1;i<=100;i++){System.out.println(i);//循环体}System.out.println("for循环结束");}
}

package com.HJX.Struct;public class For_Demo02 {public static void main(String[] args) {//练习1:计算0--100之间的奇数和偶数的和int oddsum = 0;int evensum = 0;for (int i = 0; i < 100; i++) {if (i%2 != 0) { //奇数oddsum += i; //oddsum = oddsum + i}else { //偶数evensum += i; //evensum = evensum + i}}System.out.println("0--100之间的奇数和为:"+oddsum);System.out.println("0--100之间的偶数和为:"+evensum);}
}

package com.HJX.Struct;public class For_Demo03 {public static void main(String[] args) {//练习2:用while或for循环输出1-1000之间能被5整除的数,并且每行输出3个//println 输出完会换行//print 输出完不会换行for (int i = 0; i < 1000; i++) {if (i%5==0){System.out.print(i+"\t");}if (i%(5*3)==0){ //换行System.out.print("\n");//System.out.println();}}}
}

package com.HJX.Struct;public class For_Demo04 {public static void main(String[] args) {for (int j = 0; j <= 9; j++) {for (int i = 1; i <= j; i++) {System.out.print(j+"*"+i+"="+(j*i) + "\t");}System.out.println();}/*1*1=12*1=2	2*2=43*1=3	3*2=6	3*3=94*1=4	4*2=8	4*3=12	4*4=165*1=5	5*2=10	5*3=15	5*4=20	5*5=256*1=6	6*2=12	6*3=18	6*4=24	6*5=30	6*6=367*1=7	7*2=14	7*3=21	7*4=28	7*5=35	7*6=42	7*7=498*1=8	8*2=16	8*3=24	8*4=32	8*5=40	8*6=48	8*7=56	8*8=649*1=9	9*2=18	9*3=27	9*4=36	9*5=45	9*6=54	9*7=63	9*8=72	9*9=81*/       }
}

package com.HJX.Struct;public class For_Demo05 {public static void main(String[] args) {int[] numbers = {10,20,30,40,50}; //定义数组//遍历数组的元素for(int i=0;i<5;i++){System.out.println(numbers[i]);}System.out.println("------------");//另外一种方法for (int x:numbers){System.out.println(x);}        }
}

break & continue

package com.HJX.Struct;public class Break_Demo01 {public static void main(String[] args) {int i = 0;while (i<100){i++;System.out.println(i);if (i==30){break;}}}
}

package com.HJX.Struct;public class Continue_Demo01 {public static void main(String[] args) {int i = 0;while (i<100){i++;if (i%10==0){System.out.println();continue;}System.out.print(i+"\t");}/*1	2	3	4	5	6	7	8	911	12	13	14	15	16	17	18	1921	22	23	24	25	26	27	28	2931	32	33	34	35	36	37	38	3941	42	43	44	45	46	47	48	4951	52	53	54	55	56	57	58	5961	62	63	64	65	66	67	68	6971	72	73	74	75	76	77	78	7981	82	83	84	85	86	87	88	8991	92	93	94	95	96	97	98	99*/}
}

package com.HJX.Struct;public class Test_Demo01 {public static void main(String[] args) {//打印三角形  5行for (int i = 1; i <= 5; i++) {for (int j = 5; j >= i; j--) {System.out.print(" ");}for (int j = 1; j <= i; j++) {System.out.print("*");}for (int j = 1; j < i; j++) {System.out.print("*");}for (int j = 5; j >= i; j--) {System.out.print(" ");}System.out.println();}/***************************/}
}