java 在调取方法时出错 请各位帮看看 很是不解

Question

package study;

import java.util.Scanner;

public abstract class GuessGame {
Scanner in = new Scanner(System.in);
public void go(){
int number = (int)Math.random()*10;
int guess;
do{
guess = nextInt();
}while(guess != number);
println("猜中了");
}
public void println(String text){
print(text + "\n");
}
public abstract void print(String text);
public abstract int nextInt();

public static void main(String[] args) {
    ConsoleGame da = new ConsoleGame();
    da.go();

}

}
class ConsoleGame extends GuessGame{

@Override
public void print(String text) {
    System.out.print(text);

}
@Override
public void println(String text){
    System.out.println(text);
}

@Override
public int nextInt() {
    // TODO 自动生成的方法存根
    return in.nextInt();
}

}

Answer 1

为什么两个class会放在一个文件里？？？？？