2021.7.20

scanner

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： ");

        //判断用户有无输入字符串
        if (scanner.hasNext()){
            //使用next方式接收
            String str = scanner.next();//程序会等待用户输入完毕
            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
        scanner.close();
    }
}

package scanner;

import java.util.Scanner;

public class Demo02 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.println("使用方法nextLine接收： ");

        if (scanner.hasNext()){
            String str = scanner.nextLine();

            System.out.println("输出的内容为： "+str);
        }
        scanner.close();
    }
}

package 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("输出的内容为： "+str);

        scanner.close();
    }
}

package scanner;

import java.util.Scanner;

public class Demo04 {
    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);

        //和
        double sum = 0;

        //计算输入了多少个数字
        int m = 0;

        //通过循环判断是否还有输入，并在里面对每一次进行求和和统计
        while(scanner.hasNextDouble()){
            double x = scanner.nextDouble();
            m = m + 1;
            sum = sum + x;
        }

        System.out.println(m + "个数字的和为：" + sum);
        System.out.println(m + "个数字的平均值为：" + (sum/m));








        scanner.close();

    }
}

struck

Switch

package struct;

public class SwitchDemo01 {
    public static void main(String[] args) {
        // case穿透 // switch匹配一个具体的值


        char grade = 'A';

        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");
        }
    }
}

While循环

package struct;

public class WhileDemo01 {
    public static void main(String[] args) {
        int i = 0;
        while(i<100){
            i++;
            System.out.println(i);
        }
    }
}

DoWhile循环

package struct;

public class DoWhileDemo01 {
    public static void main(String[] args) {
        int i = 0;
        int sum = 0;
        do {
            sum = sum +i;
            i++;
        }while(i<=100);
        System.out.println(sum);
    }
}

If循环

package struct;

import java.util.Scanner;

public class IfDemo01 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.println("请输入成绩：");

        int score = scanner.nextInt();

        if (score > 60){
            System.out.println("及格");
        }else{
            System.out.println("不及格");
        }

        scanner.close();
    }
}

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==100){
            System.out.println("恭喜满分！");
        }else if (score<100 && score>=90){
            System.out.println("A");}
        else if (score<90 && score>=80){
            System.out.println("B");}
        else if (score<80 && score>=70){
            System.out.println("C");}
        else if (score<70 && score>=60){
            System.out.println("D");}
        else if((score < 60) && (score >= 0)) {
            System.out.println("不及格");}
        else {
            System.out.println("成绩不合法");
        }

        scanner.close();
    }
}

For循环

package struct;

public class ForDemo01 {
    public static void main(String[] args) {
        int a = 0;
        while (a<100){
            System.out.println(a);
            a+= 2;
        }
        System.out.println("whlie循环结束！");

        System.out.println("====================");
        int i = 0;
        for (i=0;i<100;i++){
            System.out.println(i);
        }
        System.out.println("for循环结束！");
    }
}

三个练习

计算1-100里偶数与奇数的和

package struct;

public class ForDemo02 {
    public static void main(String[] args) {
        //计算1-100里偶数与奇数的和
        int oddSum = 0;
        int evenSum = 0;
        for (int i = 0; i <= 100; i++) {
            if(i%2!=0){
                oddSum+=i;  //oddSum = oddSum + i;
            }else{
                evenSum+=i;
            }

        }

        System.out.println("奇数的和为：" + oddSum);
        System.out.println("偶数的和为：" + evenSum);

    }
}

用while或芽or循环输出1-1000之间能被5整除的数，并且每行输出3个

package struct;

public class ForDemo03 {
    public static void main(String[] args) {
        //用while或芽or循环输出1-1000之间能被5整除的数，并且每行输出3个
        for (int i = 0; i <= 1000; i++) {
            if(i%5==0){
                System.out.print(i+"\t");
            }
            if(i%15==0){
                System.out.print("\n");
                //或者System.out.println();
            }

            //println 输出完会换行
            //print   输出完不会换行

        }

    }
}

九九乘法表

package struct;

public class ForDemo04 {
    public static void main(String[] args) {
        //九九乘法表
        for (int j=1;j<=9;j++){
            for(int i=1;i<=j;i++){
                System.out.print(j+"*"+i+"="+(j*i));
            }
            System.out.println();
        }
        //1.我们先打印第一列，这个大家应该都会
        // 2.我们把固定的1再用一个循环包起来
        // 3.去掉重复项，i <= j
        //4。调整样式
    }
}