我如何使用Scanner
类从控制台读取输入?像这样的东西:
System.out.println("Enter your username: ");
Scanner = input(); // Or something like this, I don't know the code
基本上,我想要的只是让扫描仪读取用户名的输入,并将输入分配给String
变量。
我如何使用Scanner
类从控制台读取输入?像这样的东西:
System.out.println("Enter your username: ");
Scanner = input(); // Or something like this, I don't know the code
基本上,我想要的只是让扫描仪读取用户名的输入,并将输入分配给String
变量。
一个简单的例子来说明java.util.Scanner
工作原理是从System.in
. 这真的很简单。
Scanner sc = new Scanner(System.in);
int i = sc.nextInt();
要检索用户名,我可能会使用sc.nextLine()
.
System.out.println("Enter your username: ");
Scanner scanner = new Scanner(System.in);
String username = scanner.nextLine();
System.out.println("Your username is " + username);
next(String pattern)
如果您想对输入进行更多控制,或者只是验证username
变量,也可以使用。
您将在API 文档中找到有关其实现的更多信息java.util.Scanner
Scanner scan = new Scanner(System.in);
String myLine = scan.nextLine();
从控制台读取数据
BufferedReader
是同步的,因此可以从多个线程安全地完成 BufferedReader 上的读取操作。可以指定缓冲区大小,也可以使用默认大小(8192)。对于大多数用途,默认值足够大。
readLine() « 只是从流或源中逐行读取数据。一行被认为是由以下任何一个终止:\n、\r(或)\r\n
Scanner
使用分隔符模式将其输入分解为标记,默认情况下匹配空格(\s)并且它被Character.isWhitespace
.
« 在用户输入数据之前,扫描操作可能会阻塞,等待输入。 « 如果您想从流中解析特定类型的令牌,请使用 Scanner( BUFFER_SIZE = 1024 )。 « 然而,扫描仪不是线程安全的。它必须在外部同步。
next() « 从这个扫描器中查找并返回下一个完整的令牌。nextInt() « 将输入的下一个标记扫描为 int。
代码
String name = null;
int number;
java.io.BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
name = in.readLine(); // If the user has not entered anything, assume the default value.
number = Integer.parseInt(in.readLine()); // It reads only String,and we need to parse it.
System.out.println("Name " + name + "\t number " + number);
java.util.Scanner sc = new Scanner(System.in).useDelimiter("\\s");
name = sc.next(); // It will not leave until the user enters data.
number = sc.nextInt(); // We can read specific data.
System.out.println("Name " + name + "\t number " + number);
// The Console class is not working in the IDE as expected.
java.io.Console cnsl = System.console();
if (cnsl != null) {
// Read a line from the user input. The cursor blinks after the specified input.
name = cnsl.readLine("Name: ");
System.out.println("Name entered: " + name);
}
Reader Input: Output:
Yash 777 Line1 = Yash 777
7 Line1 = 7
Scanner Input: Output:
Yash 777 token1 = Yash
token2 = 777
input.nextInt() 方法有问题 - 它只读取 int 值。
因此,当使用 input.nextLine() 读取下一行时,您会收到“\n”,即Enter密钥。所以要跳过这个,你必须添加 input.nextLine()。
试试这样:
System.out.print("Insert a number: ");
int number = input.nextInt();
input.nextLine(); // This line you have to add (it consumes the \n character)
System.out.print("Text1: ");
String text1 = input.nextLine();
System.out.print("Text2: ");
String text2 = input.nextLine();
有几种方法可以从用户那里获得输入。在这个程序中,我们将使用 Scanner 类来完成任务。这个 Scanner 类在 下java.util
,因此程序的第一行是import java.util.Scanner; 它允许用户在 Java 中读取各种类型的值。导入语句行必须在 java 程序的第一行,我们继续进行代码。
in.nextInt(); // It just reads the numbers
in.nextLine(); // It get the String which user enters
要访问 Scanner 类中的方法,请创建一个新的扫描仪对象作为“in”。现在我们使用它的一种方法,即“下一步”。“next”方法获取用户在键盘上输入的文本字符串。
这里我in.nextLine();
用来获取用户输入的字符串。
import java.util.Scanner;
class GetInputFromUser {
public static void main(String args[]) {
int a;
float b;
String s;
Scanner in = new Scanner(System.in);
System.out.println("Enter a string");
s = in.nextLine();
System.out.println("You entered string " + s);
System.out.println("Enter an integer");
a = in.nextInt();
System.out.println("You entered integer " + a);
System.out.println("Enter a float");
b = in.nextFloat();
System.out.println("You entered float " + b);
}
}
import java.util.Scanner;
public class ScannerDemo {
public static void main(String[] arguments){
Scanner input = new Scanner(System.in);
String username;
double age;
String gender;
String marital_status;
int telephone_number;
// Allows a person to enter his/her name
Scanner one = new Scanner(System.in);
System.out.println("Enter Name:" );
username = one.next();
System.out.println("Name accepted " + username);
// Allows a person to enter his/her age
Scanner two = new Scanner(System.in);
System.out.println("Enter Age:" );
age = two.nextDouble();
System.out.println("Age accepted " + age);
// Allows a person to enter his/her gender
Scanner three = new Scanner(System.in);
System.out.println("Enter Gender:" );
gender = three.next();
System.out.println("Gender accepted " + gender);
// Allows a person to enter his/her marital status
Scanner four = new Scanner(System.in);
System.out.println("Enter Marital status:" );
marital_status = four.next();
System.out.println("Marital status accepted " + marital_status);
// Allows a person to enter his/her telephone number
Scanner five = new Scanner(System.in);
System.out.println("Enter Telephone number:" );
telephone_number = five.nextInt();
System.out.println("Telephone number accepted " + telephone_number);
}
}
您可以编写一个简单的程序来询问用户的姓名并打印回复使用的任何输入。
或者让用户输入两个数字,您可以对这些数字进行加、乘、减或除,然后打印用户输入的答案,就像计算器的行为一样。
所以你需要 Scanner 类。你必须import java.util.Scanner;
,并且在你需要使用的代码中:
Scanner input = new Scanner(System.in);
input
是一个变量名。
Scanner input = new Scanner(System.in);
System.out.println("Please enter your name: ");
s = input.next(); // Getting a String value
System.out.println("Please enter your age: ");
i = input.nextInt(); // Getting an integer
System.out.println("Please enter your salary: ");
d = input.nextDouble(); // Getting a double
看看这有什么不同:input.next();
,,,i = input.nextInt();
d = input.nextDouble();
根据 String,int 和 double 的变化方式与其余部分相同。不要忘记代码顶部的 import 语句。
一个简单的例子:
import java.util.Scanner;
public class Example
{
public static void main(String[] args)
{
int number1, number2, sum;
Scanner input = new Scanner(System.in);
System.out.println("Enter First multiple");
number1 = input.nextInt();
System.out.println("Enter second multiple");
number2 = input.nextInt();
sum = number1 * number2;
System.out.printf("The product of both number is %d", sum);
}
}
当用户输入他/她username
时,还要检查有效输入。
java.util.Scanner input = new java.util.Scanner(System.in);
String userName;
final int validLength = 6; // This is the valid length of an user name
System.out.print("Please enter the username: ");
userName = input.nextLine();
while(userName.length() < validLength) {
// If the user enters less than validLength characters
// ask for entering again
System.out.println(
"\nUsername needs to be " + validLength + " character long");
System.out.print("\nPlease enter the username again: ");
userName = input.nextLine();
}
System.out.println("Username is: " + userName);
import java.util.*;
class Ss
{
int id, salary;
String name;
void Ss(int id, int salary, String name)
{
this.id = id;
this.salary = salary;
this.name = name;
}
void display()
{
System.out.println("The id of employee:" + id);
System.out.println("The name of employye:" + name);
System.out.println("The salary of employee:" + salary);
}
}
class employee
{
public static void main(String args[])
{
Scanner sc = new Scanner(System.in);
Ss s = new Ss(sc.nextInt(), sc.nextInt(), sc.nextLine());
s.display();
}
}
这是执行所需操作的完整类:
import java.util.Scanner;
public class App {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
final int valid = 6;
Scanner one = new Scanner(System.in);
System.out.println("Enter your username: ");
String s = one.nextLine();
if (s.length() < valid) {
System.out.println("Enter a valid username");
System.out.println(
"User name must contain " + valid + " characters");
System.out.println("Enter again: ");
s = one.nextLine();
}
System.out.println("Username accepted: " + s);
Scanner two = new Scanner(System.in);
System.out.println("Enter your age: ");
int a = two.nextInt();
System.out.println("Age accepted: " + a);
Scanner three = new Scanner(System.in);
System.out.println("Enter your sex: ");
String sex = three.nextLine();
System.out.println("Sex accepted: " + sex);
}
}
读取输入:
Scanner scanner = new Scanner(System.in);
String input = scanner.nextLine();
在调用带有一些参数/参数的方法时读取输入:
if (args.length != 2) {
System.err.println("Utilizare: java Grep <fisier> <cuvant>");
System.exit(1);
}
try {
grep(args[0], args[1]);
} catch (IOException e) {
System.out.println(e.getMessage());
}
有一种从控制台读取的简单方法。
请找到以下代码:
import java.util.Scanner;
public class ScannerDemo {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
// Reading of Integer
int number = sc.nextInt();
// Reading of String
String str = sc.next();
}
}
详细了解请参考以下文档。
现在让我们谈谈对Scanner类工作的详细理解:
public Scanner(InputStream source) {
this(new InputStreamReader(source), WHITESPACE_PATTERN);
}
这是创建 Scanner 实例的构造函数。
在这里,我们传递的InputStream
只是一个System.In
. 在这里它打开了InputStream
用于控制台输入的管道。
public InputStreamReader(InputStream in) {
super(in);
try {
sd = StreamDecoder.forInputStreamReader(in, this, (String)null); // ## Check lock object
}
catch (UnsupportedEncodingException e) {
// The default encoding should always be available
throw new Error(e);
}
}
通过传递 System.in,此代码将打开套接字以从控制台读取。
您可以流动此代码:
Scanner obj= new Scanner(System.in);
String s = obj.nextLine();
您可以在 Java 中使用 Scanner 类
Scanner scan = new Scanner(System.in);
String s = scan.nextLine();
System.out.println("String: " + s);
import java.util.Scanner; // Import the Scanner class
class Main { // Main is the class name
public static void main(String[] args) {
Scanner myObj = new Scanner(System.in); // Create a Scanner object
System.out.println("Enter username");
String userName = myObj.nextLine(); // Read user input
System.out.println("Username is: " + userName); // Output user input
}
}