[Java Process Control Learning] User Interaction Scanner

Scanner object

Used to realize the interaction between programs and people, Java.util.Scanner is a new feature of java5, and we can get user input through the Scanner class.

Basic syntax:

Scanner s = new Scanner(System.in);

Get the input string through the next() and nextLine() methods of the Scanner class. Before reading, we generally need to use hasNext() " Is there a next one, with if statement " and hasNextLine() " Is there a next line? , With the if statement " to determine whether there is still input data.

import java.util.Scanner;、//导入Scanner包，自动

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 s =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 (s.hasNext()==true){
    
    
            //使用next方式接收
            String str =s.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.要养成好习惯用完就关掉
        s.close();
    }
}

next():

Breaks if there is a space

• 1. You must read valid characters before you can end the input

• 2. For the blanks encountered before entering valid characters, the next() method will automatically remove them.

• 3. Only after valid characters are entered, the blanks entered after them are used as separators or terminators.

• 4. next() cannot get a string with spaces.

if (s.hasNext()==true){ //Use the next method to receive String str =s.next();//The program will wait for the user to input System.out.println("The output content is:"+str );

nextLine():

It will be broken if there is a carriage return

• 1. Take Enter as the terminator, which means that the nextLine() method returns all the characters before the carriage return.

• 2. You can get blanks.

  if(scanner.hasNextLine()){
        
        
      String str= scanner.nextLine();    //等待用户去输入
      System.out.println("输出的内容为："+str);
  

nextInt ():

Integer

End with a space

nextflout():

Float type
ends with a space

Example:

import java.util.Scanner;

public class Demo04 {
    
    
    public static void main(String[] args) {
    
    
        Scanner s =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：");

        //如果。。。那么
        if(s.hasNextInt()){
    
       //判断输入的是否还有整数
            i=s.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(s.hasNextFloat()){
    
        //小数型
            f=s.nextFloat();
            System.out.println("小数数据："+f);
        }else{
    
    
            System.out.println("输入的不是小数数据！");
        }


        s.close();
    }
} 

Application questions:

We can enter multiple numbers, and find the sum and average. Each number is confirmed with Enter, and the input is terminated by entering a non-number and the execution result is output:

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);

        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("你输入了第"+m+"个数据,然后当前结果sum="+sum);
        }
        System.out.println(m+"个数的和为"+sum);
        System.out.println(m+"个数的平均值是"+(sum/m));

        scanner.close();
    }
}