В чем проблема?
package com.javarush.task.task07.task0721;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
/*
Минимаксы в массивах
*/
public class Solution {
public static void main(String[] args) throws IOException {
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
int[] array = new int [20];
int max = 0;
int min = 0;
for(int i =0; i < array.length; i++){
array[i] = Integer.parseInt(reader.readLine());
if(array[i] > max)
max = array[i];
if(array[i] < min)
min = array[i];
}
System.out.print(max + " " + min);
}
}