Janken.java

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

public class Janken {
    static Random rg = new Random();
    
    public static void main(String[] args) throws Exception {
        int comp;
        // 0～2までの乱数をint型の変数compに求める
        comp=rg.nextInt(3);
        // 試しで、変数compを出力する
        System.out.print(""+comp);
        
        // Here your code !
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String line = br.readLine();
    }
}

Main.java

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

public class Main {
    static Random rg = new Random();
    
    public static void main(String[] args) throws Exception {
        int comp;
        // 0～2までの乱数をint型の変数compに求める
        comp=rg.nextInt(3);
        // 試しで、変数compを出力する
        System.out.print(""+comp);
        
        // Here your code !
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String line = br.readLine();
    }
}