Java Gossip: 取得使用者输入

UserInput.java:1: cannot resolve symbol
symbol : class Scanner
location: package util
import java.util.Scanner;
^
UserInput.java:5: cannot resolve symbol
symbol : class Scanner
location: class UserInput
Scanner scanner = new Scanner(System.in);
^
UserInput.java:5: cannot resolve symbol
symbol : class Scanner
location: class UserInput
Scanner scanner = new Scanner(System.in);
^
3 errors
这是为什么？

程序如下：
import java.util.Scanner;

public class UserInput {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.print("Please input your name: ");
System.out.printf("Hello! %s!", scanner.next());
}
}

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