練習用アプリ：じゃんけん

Janken.java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.text.Normalizer;
import java.util.HashMap;
import java.util.Map;

/**
 *
 * @author ihcomega
 */
public class Janken {

    private final String ROCK = "グー";
    private final String PAPER = "パー";
    private final String SCISSORS = "チョキ";

    private int win;
    private int loss;

    Map<String, String> results;
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));

    public Janken() {
        results = new HashMap<>();
        results.put(ROCK, PAPER);
        results.put(PAPER, SCISSORS);
        results.put(SCISSORS, ROCK);
    }

    private String decideShape() {
        int shape = (int) (Math.random() * 3 + 1);
        return Integer.toString(shape);
    }

    private String transferNum(String num) {
        switch (num) {
            case "1":
                return "グー";
            case "2":
                return "チョキ";
            case "3":
                return "パー";
            default:
                throw new IllegalArgumentException();
        }
    }

    private boolean isTied(String formedShape, String selectedShape) {
        if (formedShape.equals(selectedShape)) {
            System.out.println("あなたは" + formedShape + "、わたしも" + selectedShape + "。あいこ！もう1回！");
            return true;
        } else {
            return false;
        }
    }

    private void printResult(String formedShape, String selectedShape) throws NullPointerException {
        String strongerShape = results.get(formedShape);
        if (strongerShape.equals(selectedShape)) {
            loss++;
            System.out.println("あなたは" + formedShape + "で、わたしは" + selectedShape + "。わたしの勝ち！");
        } else {
            win++;
            System.out.println("あなたは" + formedShape + "で、わたしは" + selectedShape + "。あなたの勝ち！");
        }
        System.out.println("いま、" + win + "勝" + loss + "敗だよ！");
    }

    private void match() throws IOException {
        String formedShape;
        String selectedShape;

        System.out.println("1 グー");
        System.out.println("2 チョキ");
        System.out.println("3 パー");
        System.out.print("1〜3の数字を打ち込んでEnter押してね！⇛");

        String inputText = Normalizer.normalize(in.readLine().trim(), Normalizer.Form.NFKD);
        formedShape = transferNum(inputText);
        selectedShape = transferNum(decideShape());

        if (isTied(formedShape, selectedShape)) {
            match();
        } else {
            printResult(formedShape, selectedShape);
            repeat();
        }
    }

    private void repeat() throws IOException {
        System.out.println("");
        System.out.println("もう1回？");
        System.out.println("続けるなら何か入力してEnterを押してね！やめるならEnterのみ押してね！");

        String inputText = in.readLine();
        if (!inputText.isEmpty()) {
            System.out.println("よし、もう1回〜");
            match();
        } else {
            System.out.println("おしまい。またね。");
        }
    }

    public static void main(String... args) {
        Janken janken = new Janken();
        try {
            System.out.println("じゃんけんするよ！何出す？？");
            janken.match();
        } catch (IOException | NullPointerException e) {
            System.err.println("エラーや！");
        } catch (IllegalArgumentException e) {
            System.err.println("1か2か3だけを入れてね！！！");
        }
    }
}