从控制台读取数据

BufferedReader is synchronized, so read operations on a BufferedReader can be safely done from multiple threads. The buffer size may be specified, or the default size(8192) may be used. The default is large enough for most purposes. readLine() « just reads data line by line from the stream or source. A line is considered to be terminated by any one these: \n, \r (or) \r\n Scanner breaks its input into tokens using a delimiter pattern, which by default matches whitespace(\s) and it is recognised by Character.isWhitespace. « Until the user enters data, the scanning operation may block, waiting for input. « Use Scanner(BUFFER_SIZE = 1024) if you want to parse a specific type of token from a stream. « A scanner however is not thread safe. It has to be externally synchronized. next() « Finds and returns the next complete token from this scanner. nextInt() « Scans the next token of the input as an int.

Code

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);
}

流的输入和输出

Reader Input:     Output:
Yash 777          Line1 = Yash 777
     7            Line1 = 7

Scanner Input:    Output:
Yash 777          token1 = Yash
                  token2 = 777

您可以编写一个简单的程序来询问用户的姓名，并打印任何回复使用的输入。

或者要求用户输入两个数字，您可以对这些数字进行加、乘、减或除，并像计算器一样打印用户输入的答案。

这里你需要Scanner类。你必须导入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类型，int类型和double类型的变化方式与其他类型相同。不要忘记代码顶部的import语句。

下面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);
    }
}

你可以流动这段代码:

Scanner obj= new Scanner(System.in);
String s = obj.nextLine();

当用户输入他/她的用户名时，也检查是否有有效的输入。

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);

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类属于java。util，因此程序的第一行是import java.util.Scanner;它允许用户读取Java中各种类型的值。import语句行必须在java程序的第一行中，我们将进一步处理代码。

in.nextInt(); // It just reads the numbers

in.nextLine(); // It get the String which user enters

为了访问Scanner类中的方法，创建一个新的Scanner对象作为“in”。现在我们用它的一种方法，那就是“next”。“next”方法获取用户在键盘上输入的文本字符串。

这里我使用in.nextLine();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);
    }
}