Scanner

使用示例：

public class DemoSanner02 {
    public static void main(String[] args) {
        //创建一个扫描器的对象，用于接收键盘数据
        Scanner scanner = new Scanner(System.in);
        System.out.println("使用next方式接收：");
        if(scanner.hasNext()) {
            //使用next接收
            String str = scanner.next();//只接受空格前一个单词
            System.out.println("输出的内容为：" +str);
        }
        //判断用户有没有输入字符串
        if(scanner.hasNextLine()) {
            //使用next接收
            String str = scanner.nextLine();//接受一行单词
            System.out.println("输出的内容为：" +str);
        }
        //凡是使用IO流的对象，用完必须关闭
        scanner.close();
    }
}

        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();

public class ScannerPractice {
    public static void main(String[] args) {
        //输入多个数字，求和，遇到非数字退出系统
        Scanner scanner = new Scanner(System.in);
        //和
        double sum = 0;
        int num = 0;
        while(scanner.hasNextDouble()) {
            double x = scanner.nextDouble();
            num += 1;
            sum += x;
        }
        double avg = sum / num;
        System.out.println("和是："+sum);
        System.out.println("平均值："+avg);
        scanner.close();
    }
}

顺序、选择、循环结构：

package Sequence;
import java.util.Scanner;
public class demo01 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入内容：");
        if (scanner.hasNextInt()) {
            int score = scanner.nextInt();
            if (score > 60) {
                System.out.println("及格！");
            }
            else {
                System.out.println("不及格！");
            }
        }
        else if (scanner.hasNextDouble()) {
            System.out.println("成绩不是整数！");
        }
        else {
            System.out.println("不是数字");
        }
        scanner.close();
    }
}

public class For {
    public static void main(String[] args) {
        int[] numbers = {10,20,30,40};
        //格式1
        for(int i = 0; i < 4; i++) {
            System.out.println(numbers[i]);
        }
        //格式2
        for(int x :numbers) {
            System.out.println(x);
        }
    }
}

public class BreakContinue {
    public static void main(String[] args) {
        for(int i = 0; i < 10; i++) {
            if(i == 5) {
                continue;
            }
            if (i == 7) {
                break;
            }
            System.out.print(i);
        }
    }
}

package circulation;
public class While {
    public static void main(String[] args) { 
        int i = 0;
        int sum = 0;
        //格式1
        while(i <= 100) {
            sum += i;
            i += 1; //i++
        }
        //格式2
        do {
            sum += i;
            i += 1;
        }while(i <= 100);
        System.out.println(sum);
    }
}