Progateで学んだことはすぐにアウトプットしないと無駄になる理由

import java.util.Scanner;

public class Main {

// 選択用メソッド
	public static int select(String title) {
		System.out.println(title);
		System.out.println("[0]：たしざんをする");
		System.out.println("[1]：ひきざんをする");
		System.out.println("[2]：かけざんをする");
		System.out.println("[3]：やりません");
		System.out.print("せんたく してください：");
		int number = new Scanner(System.in).nextInt();
		return number;
	}
// 計算式を分岐
	public static void branch(String name, int number) {
		if (number == 0) {
			 Format.calc(name,number);		 
		} else if (number == 1) {
			Format.calc(name,number);
		} else if (number == 2) {
			Format.calc(name,number);
		} else if (number == 3) {
			System.out.println("またきてね");
		} else {
			System.out.println("そんな　すうじは　ないよ");
		}
	}

	public static void main(String[] args) throws InterruptedException {
		System.out.println("あなたの なまえを おしえてください");
		String name = new Scanner(System.in).next();
		System.out.println("こんにちは" + " " + name);
		
		String start = "テストにちょうせんしますか？";
		String repray = "もう一度挑戦しますか？";
		
		int number = select(start);
		branch(name, number);
		select(repray);
		branch(name, number);
	}
}

import java.util.Random;
import java.util.Scanner;

public class Format {
	public static void calc(String name, int number) {
		long start_point = System.currentTimeMillis();
		int score = 0;
		for(int i = 1; i <= 10; i++) {
			switch (number) {
//	足し算の処理
				case 0:
					int a = new Random().nextInt(9)+1;
					int b = new Random().nextInt(9)+1;
					int answer = a + b;
					
					System.out.println( i + "もんめ");
					System.out.print(a + "+" + b + "=");
					int guess = new Scanner(System.in).nextInt();
					if (guess == answer) {
						System.out.println("だいせいかい");
						score += 10;
					} else {
						System.out.println("まちがいです");
					}
					break;
//	引き算の処理
				case 1:
					int c = new Random().nextInt(5)+5;
					int d = new Random().nextInt(9)+1;
					int answer1 = c - d;
					
					System.out.println( i + "もんめ");
					System.out.print( c + "-" + d + "=");
					int guess1 = new Scanner(System.in).nextInt();
					if (guess1 == answer1) {
						System.out.println("だいせいかい");
						score += 10;
					} else {
						System.out.println("まちがいです");
					}
					break;
//	掛け算の処理
				case 2:
					int e = new Random().nextInt(9)+1;
					int f = new Random().nextInt(9)+1;
					int answer2 = e * f;
					
					System.out.println( i + "もんめ");
					System.out.print(e + "×" + f + "=");
					int guess2 = new Scanner(System.in).nextInt();
					if (guess2 == answer2) {
						System.out.println("だいせいかい");
						score += 10;
					} else {
						System.out.println("まちがいです");
					}
					break;
				}
				
		}
		long end_point = System.currentTimeMillis();
		long time_seconds = (end_point - start_point) / 1000 % 60;
		long time_minutes = (end_point - start_point) / 1000 / 60;
		System.out.println(name + "のスコアは" + score + "てん です");
		if(score == 100) {
			System.out.println("かんぺきだ！ まんてんですね");
		} else if (score >= 80) {
			System.out.println("すばらしい そのちょうしです");
		} else if (score >= 40) {
			System.out.println("いいですね");
		} else {
			System.out.println("がんばったね");
		}
		System.out.println("じかんは" + time_minutes + "ふん" + time_seconds + "びょう でした");
	}
	
}