Test8.java

/*
 * 김소은
 * 과제8. 연소득 과세금액 계산 프로그램
 *
 * 과세계산과 관련된 변수, 함수를 묶어 Taxation 클래스와 단계별 과세 정보를 담는 TaxationSection 클래스를 만들었습니다.
 * 각 클래스는 메소드만 호출할 수 있도록 하여 캡슐화했습니다.
 * 입력값이 잘못됐으면 재입력할 수 있도록 구현하였습니다.
 */

import java.util.InputMismatchException;
import java.util.Scanner;

class Taxation {
	private final TaxationSection[] taxationSections;

	public Taxation() {
		taxationSections = new TaxationSection[] {
				new TaxationSection(12000000, 0.06f, 0),
				new TaxationSection(46000000, 0.15f, 1080000),
				new TaxationSection(88000000, 0.24f, 5220000),
				new TaxationSection(150000000, 0.35f, 14900000),
				new TaxationSection(300000000, 0.38f, 19400000),
				new TaxationSection(500000000, 0.4f, 25400000),
				new TaxationSection(1000000000, 0.42f, 35400000),
				new TaxationSection(Long.MAX_VALUE, 0.45f, 65400000)
		};
	}

	public float getTariff(int level) {
		return taxationSections[level].getTariff();
	}

	public long calculateTaxByProgressiveDeduction(long annualIncome, int level) {
		return taxationSections[level].calculateTaxByProgressiveDeduction(annualIncome);
	}

	public long calculateTaxBaseTerm(int level) {
		if (level == 0) {
			return taxationSections[level].getTaxBase();
		} else {
			return taxationSections[level].getTaxBase() - taxationSections[level - 1].getTaxBase();
		}
	}
}

class TaxationSection {
	private final long taxBase;					// 과세표준
	private final float tariff;					// 세율
	private final long progressiveDeduction;	// 누진공제액

	public TaxationSection(long taxBase, float tariff, long progressiveDeduction) {
		this.taxBase = taxBase;
		this.tariff = tariff;
		this.progressiveDeduction = progressiveDeduction;
	}

	public long getTaxBase() {
		return taxBase;
	}

	public float getTariff() {
		return tariff;
	}

	public long calculateTaxByProgressiveDeduction(long annualIncome) {
		return (long)(annualIncome * tariff) - progressiveDeduction;
	}
}

public class Test8 {
	private static Scanner scanner;

	public static void main(String[] args) {
		scanner = new Scanner(System.in);

		System.out.println("[과세금액 계산 프로그램]");

		long annualIncome = inputAnnualIncome();

		Taxation taxation = new Taxation();

		int level = 0;
		long totalTax = 0;
		long annualIncomeRest = annualIncome;
		while (annualIncomeRest > 0) {
			// 단계 별 세금 계산
			long taxBaseTerm = taxation.calculateTaxBaseTerm(level);
			long incomeByLevel = Math.min(annualIncomeRest, taxBaseTerm);
			long tax = (long)(incomeByLevel * taxation.getTariff(level));

			printTaxByLevel(incomeByLevel, (int)(taxation.getTariff(level) * 100), tax);

			totalTax += tax;
			annualIncomeRest -= incomeByLevel;
			level++;
		}
		level--;

		System.out.println();
		System.out.println("[세율에 의한 세금]:\t\t\t" + totalTax);
		System.out.println("[누진공제 계산에 의한 세금]:\t" + taxation.calculateTaxByProgressiveDeduction(annualIncome, level));

		closeResource();
	}

	private static int inputAnnualIncome() {
		int annualIncome = 0;
		boolean isValid = false;

		while (! isValid) {
			System.out.print("연소득을 입력해 주세요.:");

			try {
				checkIntType();

				annualIncome = scanner.nextInt();
				checkValidAnnualIncome(annualIncome);

				isValid = true;
			} catch (InputMismatchException e) {
				System.out.println(e.getMessage());
			}
		}

		return annualIncome;
	}

	private static void checkIntType() {
		if (! scanner.hasNextInt()) {
			removeBuffer();
			throw new InputMismatchException("숫자만 입력 가능합니다.");
		}
	}

	private static void checkValidAnnualIncome(long annualIncome) {
		if (annualIncome < 0) {
			throw new InputMismatchException("소득 값은 0 이상이어야 합니다.");
		}
	}

	private static void removeBuffer() { scanner.next(); }

	private static void printTaxByLevel(long incomeByLevel, int tariffPercent, long taxByLevel) {
		System.out.printf("%12d * %2d%% = %12d\n", incomeByLevel, tariffPercent, taxByLevel);
	}

	private static void closeResource() { scanner.close(); }
}