Java 什么是system.in
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What is system.in
提问by user3762764
Consider this Scannerinput example.
考虑这个Scanner输入示例。
Scanner user_input = new Scanner( System.in );
Here Scanneris the CLASS.
user_inputis the OBJECT under Scanner class.
What is (System.in)? Is it a parameter passed or a object under Scannerclass?.
这里Scanner是类。
user_input是 Scanner 类下的 OBJECT。什么是（System.in）？是传递的参数还是Scanner类下的对象？
Consider another example.
考虑另一个例子。
dog dog1 = new dog(25)
Here I have set dog class to accept size as a parameter.
在这里，我已将狗类设置为接受大小作为参数。
What exactly is System.in?
究竟是System.in什么？
回答by ltalhouarne
System.inis the "standard" input stream.
System.in是“标准”输入流。
Take a look at the following documentation: http://docs.oracle.com/javase/7/docs/api/java/lang/System.html
看看下面的文档：http: //docs.oracle.com/javase/7/docs/api/java/lang/System.html
回答by Suresh Atta
Scanner class accepts input stream as a parameter and System class have a static variable inwhich is of type InputStream. System.ingives you a instance of of type InputStream.
Scanner 类接受输入流作为参数，而 System 类有一个in类型为 的静态变量InputStream。System.in给你一个 type 的实例InputStream。
Check this doc of public static final InputStream in
检查这个 doc of public static final InputStream in
The "standard" input stream. This stream is already open and ready to supply input data.
“标准”输入流。此流已打开并准备好提供输入数据。
回答by Suresh Atta
From the source:
从来源：
System.in is an InputStream which is typically connected to keyboard input of console programs. System.in is not used as often since data is commonly passed to a command line Java application via command line arguments, or configuration files. In applications with GUI the input to the application is given via the GUI. This is a separate input mechanism from Java IO.
System.in 是一个 InputStream，它通常连接到控制台程序的键盘输入。System.in 并不经常使用，因为数据通常通过命令行参数或配置文件传递到命令行 Java 应用程序。在具有 GUI 的应用程序中，应用程序的输入是通过 GUI 提供的。这是一种独立于 Java IO 的输入机制。
回答by Praveen Chaurasiya
Scanner class has a constructor Scanner(InputStream) in its profile i.e when we call Scanner() constructor during the object creation time it will let you to pass the object of InputStream class.
Scanner 类在其配置文件中有一个构造函数 Scanner(InputStream) ，即当我们在对象创建期间调用 Scanner() 构造函数时，它将让您传递 InputStream 类的对象。
"in" is an object of "InputStream" class defined in System class(like "out" is an object of PrintStream class defined in System class).
“in”是System类中定义的“InputStream”类的对象（如“out”是System类中定义的PrintStream类的对象）。
Thus System.in is nothing but calling the "in" object of InputStream class defined in System class when Scanner constructor is called during object creation time.
因此 System.in 只不过是在对象创建期间调用 Scanner 构造函数时调用 System 类中定义的 InputStream 类的“in”对象。
Scanner(InputStream) is pre-defined constructor in Scanner class which when calls requires the object of InputStream class as the parameter and that object is System.in.
Scanner(InputStream) 是 Scanner 类中预定义的构造函数，调用时需要 InputStream 类的对象作为参数，该对象为 System.in。
回答by coders hub
System.inis used to get input from the user. Consider the following example:
System.in用于获取用户的输入。考虑以下示例：
import java.util.Scanner;
class Method {
public static void main(String args[]) {
Scanner sc=new Scanner(System.in);
System.out.println("Enter Name");
String s=sc.next();
System.out.println("Enter roll number");
int r=sc.nextInt();
System.out.println("Enter marks");
float t=sc.nextFloat();
System.out.println("Name:" + s);
System.out.println("Roll No.:" + r);
System.out.println("Marks:" + t);
}
}
Output:
输出：
Enter Name
Roshal
Enter roll number
204
Enter marks
65
Name:Roshal
Roll No.:204
Marks:65.0
输入名字
罗沙尔
输入卷号
204
输入标记
65
姓名：罗沙尔
卷号：204
分数：65.0
For explanation of this code visit: Accepting input in java
有关此代码的说明，请访问： Accepting input in java
回答by Vinita Tyagi
System.inin java means to take input from the keyboard or user.
System.outin java means to print the output to console.
System.in在 java 中意味着从键盘或用户获取输入。
System.out在 java 中意味着将输出打印到控制台。
回答by Eric H.
The Scanner constructor's parameter System.inreferences the static InputStream field indefined in the final System class. As a static field inrequires its class identifier.
Scanner 构造函数的参数System.in引用了最终 System 类中定义的静态 InputStream 字段。作为静态字段in需要其类标识符。
Oracle states that inis the "standard" input stream1, not that System.in is. The quotes around standard likely refer to the irony that inputting from a keyboard using a command line interface is no longer thestandard, what with them newfangled GUIs and all.
Oracle 声明in是“标准”输入流1，而不是 System.in 。标准周围的引号可能是指具有讽刺意味的是，使用命令行界面从键盘输入不再是标准，新奇的 GUI 等等。
