Detailed explanation of the use of nanny scanner class

One 、Scanner Class introduction
Scanner Class is in jdk1.5 Version introduced , It's in java Of util Under tool kit , It is mainly used to scan the text entered by the user from the console .
When we need to input data through the console , Just import in advance java.util In bag Scanner class , And then call Scanner class ,
Our program can get the data we input on the console .

Two 、 How to use Scanner class

1、 First, import. java.util.Scanner package ;

import java.util.Scanner;

2、 establish Scanner Class object

Scanner sc = new Scanner(System.in);

3、 Create a variable to receive the input data

// Use the above created sc Object calls the corresponding method , The console can wait for user input , We can customize a variable to receive 
// We want to input different types of data , You also need to call different methods , The specific application is as follows ：
String str = sc.nextLine();
String str = sc.next();
byte a1= sc.nextByte();
short a2= sc.nextShort();
int a3 = sc.nextInt();
long a4 = sc.nextLong();
float a5 = sc.nextFloat();
double a6 = sc.nextDouble();
boolean a7 = sc.nextBoolean();

4、 close Scanner class

// Use up Scanner after , We must remember to turn it off !
// Because use Scanner In essence, it opens a IO flow , If it's not closed , It will always occupy system resources .
sc.close();
// But be careful once you turn it off , Even in sc.close() After this line of code, you can re new Scanner(System.in), Then you can't turn on a scanner again , As shown in the figure below, you will find that the program will report errors 
// So you must turn off the scanner after you don't need it , Namely the sc.close() Put the code at the end .

3、 ... and 、next() and nextLine() The difference between （ Very important ）
From the above explanation , We will find that when the data type we want to input is String when , We have two methods to call ：next() and nextLine(). What is the difference between these two methods ？ Let's move on ：
（1） Let's test it first next()：

After using multiple sets of test cases , It is not difficult to draw the following conclusions by analyzing the output results （ Only classic test cases are posted here , Others can test by themselves ）：
next() Method when identifying the input string , We can't get the string with spaces we entered , Just read hello.
This explanation next() After reading a valid character, it will take a space as its own reading end identifier , Because we can find hello The preceding space does not affect the reading of the method . therefore next() The usage is summarized as follows ：

next() Usage Summary ：
1.  You must read valid characters before you can end the input .
2.  The blank space encountered before the valid characters entered , It will be automatically removed .
3.  Only after a valid character is entered, the blank space entered after it is used as the closing character .
4. next() Cannot get string with space .
5.  After reading , This method will position our mouse on the line where we input data .

（2） Let's test it again nextLine()：

The analysis found that , The input result is completely consistent with the input result ,nextLine() The reading result is not affected by the space in the middle of the string .
This is because the method uses carriage return （ That is our keyboard enter key ） As an end identifier .

nextLine() Usage Summary ：
1、 Take carriage return as the end identifier , Get all the strings entered before the carriage return （ Including Spaces ）.
2、 After reading , This method will position our mouse on the next row of the row we input data .

（3） First use nextLine Reuse next()、nextInt() No problem waiting , But first use next() and nextInt() After that, you can't follow closely nextLine Use .（ This is important ！！！）
This is because next() After these methods are read, a carriage return will follow , and nextLine The carriage return will be read directly , This leads to the fact that we haven't had time to input the data we want to input ,nextLine I thought we had entered such a situation ！
The solution is simple ： We are directly in the next() Add two after use nextLine() Just OK 了 , So the first one nextLine() Will be one ‘ For the dead ’, the second nextLine() We can input the data we want to input ！
Four 、hash×××() Simple use
We found that Scanner The instance variable of the class will also have hash The first set of methods , What are these methods for ？
Let's go directly to the test case , You can intuitively experience ：

5、 ... and 、Scanner Method summary

The meaning of this figure is actually , such as ：nextlnt(): Can only read int value , If the user enters other non integer data , The program will report an error .
Others such as nextByte()、nextDouble() And so on , Only data that matches this type can be read , So we need to match the corresponding method according to the data we enter .