不懂为什么会出现这些问题，还想问一下如何解决这种问题

import java.io.;
import java.until.Random;
public class Arithmetic{
public static void main(String args[])throws IOException{
int a,b,op,i,result=0,answer;
char opr=' ';
BufferedReader br;
br=new BufferedReader(new InputSteamReader(System.in));
Random r_dom=new Random();
for(i=1;i<=5;i++)
{ a=r_dom.nxetInt(100);
b=r_dom.nxetInt(100)+1;
op=r_dom.nextInt(4);
switch(op){
case 0:opr='+'; result=a+b; break;
case 1:opr='-'; result=a-b; break;
case 2:opr=''; result=a*b; break;
case 3:opr='/'; result=a/b; break;
}
System.out.print(i+"题:"+a+""+opr+b+"=");
answer=Integer.parseInt(br.readLine());
if(answer==result)
System.out.println("\t回答正确");
else System.out.println("\t错误！ 正确答案应为:"+result );
}
}
}

Main.java:2: error: package java.until does not exist import java.until.Random;

^ Main.java:8: error: cannot find symbol br=new BufferedReader(new InputSteamReader(System.in));

 ^ symbol: class InputSteamReader location: class Main 

Main
.java:9: error: cannot find symbol Random r_dom=new Random(); ^ symbol: class Random location: class Main

Main.java:9: error: cannot find symbol Random r_dom=new Random(); ^ symbol: class Random location: class Main 4 errors

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Random;

public class Arithmetic{
    public static void main(String args[])throws IOException {
        int a,b,op,i,result=0,answer;
        char opr=' ';
        BufferedReader br;
        br = new BufferedReader(new InputStreamReader(System.in));
        Random r_dom = new Random();
        for(i=1; i<=5; i++)
        { 
            a = r_dom.nextInt(100);
            b = r_dom.nextInt(100)+1;
            op = r_dom.nextInt(4);
            switch(op){
                case 0:opr='+'; result = a+b; break;
                case 1:opr='-'; result = a-b; break;
                case 2:opr='*'; result = a*b; break;
                case 3:opr='/'; result = a/b; break;
            }
            System.out.print(i+"题:"+a+""+opr+b+"=");
            answer = Integer.parseInt(br.readLine());
            if(answer == result)
                System.out.println("\t回答正确");
            else System.out.println("\t错误！ 正确答案应为:"+result );
        }
    }
}