【狂神说java学习笔记】四：java流程控制（用户交互Scanner、顺序结构、if选择结构、switch选择结构）

狂神说java学习笔记

---

---

java流程控制01：用户交互Scanner

import java.util.Scanner
Scanner s = new Scanner(System.in);
next() //空格作为分隔符或结束符
nextLine()//回车作为结束符
hasNext()
hasNextLine()

package scanner;import java.util.Scanner;public class Demo01 {public static void main(String[] args) {//创建一个扫描器对象，用于接收键盘数据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()){String str = scanner.next();System.out.println("输出的内容为："+str);}if(scanner.hasNext()){String str = scanner.next();System.out.println("输出的内容为："+str);}//凡是属于IO流的类如果不关闭，会一直占用资源，要养成好习惯，用完即关scanner.close();}
}

package scanner;import java.util.Scanner;public class Demo02 {public static void main(String[] args) {//创建一个扫描器对象，用于接收键盘数据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.hasNextLine()){String str = scanner.nextLine();System.out.println("输出的内容为："+str);}//凡是属于IO流的类如果不关闭，会一直占用资源，要养成好习惯，用完即关scanner.close();}
}

package scanner;import java.util.Scanner;public class Demo03 {public static void main(String[] args) {//创建一个扫描器对象，用于接收键盘数据Scanner scanner = new Scanner(System.in);System.out.println("请输入数据：");String str = scanner.nextLine();System.out.println("输出的内容为："+str);scanner.close();}
}

java流程控制02：Scanner进阶使用

package 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 scanner;import java.util.Scanner;public class Demo05 {public static void main(String[] args) {//输入多个数字，求其总和与平均数，每输入一个数字用回车确认，通过输入非数字结束输入，并输出执行结果Scanner scanner = new Scanner(System.in);double sum = 0;int m = 0;while(scanner.hasNextDouble()){double x = scanner.nextDouble();m++;sum += x;System.out.println("你输入了第"+m+"个数据，当前结果sum="+sum);}System.out.println(m+"个数的和为"+sum);System.out.println(m+"个数的平均值为"+(sum/m));scanner.close();}
}

java流程控制03：顺序结构

package struct;public class ShunXuDemo {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");}
}

java流程控制04：if选择结构

if单选择结构

package struct;import java.util.Scanner;public class ifDemo01 {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:判断字符串是否相等if(s.equals("Hello")){System.out.println(s);}System.out.println("End");scanner.close();}
}

if双选择结构

package struct;import java.util.Scanner;public class ifDemo02 {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>=60){System.out.println("及格");}else{System.out.println("不及格");}scanner.close();}
}

if多选择结构

package struct;import java.util.Scanner;public class ifDemo03 {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(score<100 && score>=90){System.out.println("A级");}else if(score<90 && score>=80){System.out.println("B级");}else if(score<80 && score>=70){System.out.println("C级");}else if(score<70 && score>=60){System.out.println("D级");}else if(score<60 && score>=0){System.out.println("不及格");}else{System.out.println("成绩不合法");}scanner.close();}
}

java流程控制05：switch选择结构

package struct;public class SwitchDemo01 {public static void main(String[] args) {char grade = 'D';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("再接再厉");break;case 'E':System.out.println("挂科");break;default:System.out.println("未知等级");}}
}

package struct;public class SwitchDemo02 {public static void main(String[] args) {//字符的本质还是数字//反编译 java---class(字节码文件)---反编译工具（IDEA打开class文件）String name = "中国";switch (name){case "中国":System.out.println("中");break;case "日本":System.out.println("小日子");break;default:System.out.println("华夏");}}
}