Java8 streamサンプル

AggregateSample.java

import java.util.ArrayList;
import java.util.Scanner;

public class AggregateSample {

	public static final String LINE_SEPARATOR_PATTERN = "\\r\\n|[\\n\\r\\u2028\\u2029\\u0085]";

    public static void main(String[] args) {
    	ArrayList<Integer> dataList = new ArrayList<>();
    	Scanner scan = new Scanner(System.in);
    	scan.useDelimiter("\n");
		String line;
		for (; scan.hasNext();) {
			line = scan.next();
			if(line.matches(LINE_SEPARATOR_PATTERN)) {
				break;
			}
			line = line.replaceAll(LINE_SEPARATOR_PATTERN, "");
			try {
				dataList.add(Integer.valueOf(line));
			}catch(NumberFormatException e) {
				System.err.println("数字を入力してください。");
			}
		}
		if(dataList.isEmpty()) {
			System.out.println("数字が入力されていませんでした。");
		}else {
			OutputResult(dataList);
		}

		scan.close();
    }

    private static void OutputResult(ArrayList<Integer> dataList) {
    	System.out.println("データ数：" + dataList.size());
    	System.out.println("合計：" + dataList.stream().mapToInt(x -> x).sum());
    	System.out.println("平均値：" + dataList.stream().mapToInt(x -> x).average().getAsDouble());
    	System.out.println("最小値：" + dataList.stream().min((a, b) -> a.compareTo(b)).get());
    	System.out.println("最大値：" + dataList.stream().max((a, b) -> a.compareTo(b)).get());
    }
}