贷款计算器- 等额本金、等额本息工具类(Java版)

/**  
 * Description:等额本金工具类  
 * Copyright: Copyright (Corporation)2015  
 * Company: Corporation  
 * @version: 1.0  
 * Modification History:  
 * Modified by :   
 */
package com.base.framework.core.util;

import java.math.BigDecimal;
import java.util.HashMap;
import java.util.Map;

/**
 * 等额本金是指一种贷款的还款方式,是在还款期内把贷款数总额等分,每月偿还同等数额的本金和剩余贷款在该月所产生的利息,这样由于每月的还款本金额固定,
 * 而利息越来越少,借款人起初还款压力较大,但是随时间的推移每月还款数也越来越少。
 */
public class AverageCapitalUtils {

    /**
     * 等额本金计算获取还款方式为等额本金的每月偿还本金和利息
     * 
     * 公式:每月偿还本金=(贷款本金÷还款月数)+(贷款本金-已归还本金累计额)×月利率
     * 
     * @param invest
     *            总借款额(贷款本金)
     * @param yearRate
     *            年利率
     * @param month
     *            还款总月数
     * @return 每月偿还本金和利息,不四舍五入,直接截取小数点最后两位
     */
    public static Map getPerMonthPrincipalInterest(double invest, double yearRate, int totalMonth) {
        Map map = new HashMap();
        // 每月本金
        double monthPri = getPerMonthPrincipal(invest, totalMonth);
        // 获取月利率
        double monthRate = yearRate / 12;
        monthRate = new BigDecimal(monthRate).setScale(6, BigDecimal.ROUND_DOWN).doubleValue();
        for (int i = 1; i <= totalMonth; i++) {
            double monthRes = monthPri + (invest - monthPri * (i - 1)) * monthRate;
            monthRes = new BigDecimal(monthRes).setScale(2, BigDecimal.ROUND_DOWN).doubleValue();
            map.put(i, monthRes);
        }
        return map;
    }

    /**
     * 等额本金计算获取还款方式为等额本金的每月偿还利息
     * 
     * 公式:每月应还利息=剩余本金×月利率=(贷款本金-已归还本金累计额)×月利率
     * 
     * @param invest
     *            总借款额(贷款本金)
     * @param yearRate
     *            年利率
     * @param month
     *            还款总月数
     * @return 每月偿还利息
     */
    public static Map getPerMonthInterest(double invest, double yearRate, int totalMonth) {
        Map inMap = new HashMap();
        double principal = getPerMonthPrincipal(invest, totalMonth);
        Map map = getPerMonthPrincipalInterest(invest, yearRate, totalMonth);
        for (Map.Entry entry : map.entrySet()) {
            BigDecimal principalBigDecimal = new BigDecimal(principal);
            BigDecimal principalInterestBigDecimal = new BigDecimal(entry.getValue());
            BigDecimal interestBigDecimal = principalInterestBigDecimal.subtract(principalBigDecimal);
            interestBigDecimal = interestBigDecimal.setScale(2, BigDecimal.ROUND_DOWN);
            inMap.put(entry.getKey(), interestBigDecimal.doubleValue());
        }
        return inMap;
    }

    /**
     * 等额本金计算获取还款方式为等额本金的每月偿还本金
     * 
     * 公式:每月应还本金=贷款本金÷还款月数
     * 
     * @param invest
     *            总借款额(贷款本金)
     * @param yearRate
     *            年利率
     * @param month
     *            还款总月数
     * @return 每月偿还本金
     */
    public static double getPerMonthPrincipal(double invest, int totalMonth) {
        BigDecimal monthIncome = new BigDecimal(invest).divide(new BigDecimal(totalMonth), 2, BigDecimal.ROUND_DOWN);
        return monthIncome.doubleValue();
    }

    /**
     * 等额本金计算获取还款方式为等额本金的总利息
     * 
     * @param invest
     *            总借款额(贷款本金)
     * @param yearRate
     *            年利率
     * @param month
     *            还款总月数
     * @return 总利息
     */
    public static double getInterestCount(double invest, double yearRate, int totalMonth) {
        BigDecimal count = new BigDecimal(0);
        Map mapInterest = getPerMonthInterest(invest, yearRate, totalMonth);

        for (Map.Entry entry : mapInterest.entrySet()) {
            count = count.add(new BigDecimal(entry.getValue()));
        }
        return count.doubleValue();
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        double invest = 10000; // 本金
        int month = 12;
        double yearRate = 0.15; // 年利率
        Map getPerMonthPrincipalInterest = getPerMonthPrincipalInterest(invest, yearRate, month);
        System.out.println("等额本金---每月本息:" + getPerMonthPrincipalInterest);
        double benjin = getPerMonthPrincipal(invest, month);
        System.out.println("等额本金---每月本金:" + benjin);
        Map mapInterest = getPerMonthInterest(invest, yearRate, month);
        System.out.println("等额本金---每月利息:" + mapInterest);

        double count = getInterestCount(invest, yearRate, month);
        System.out.println("等额本金---总利息:" + count);
    }
}
/**  
 * Description:等额本息工具类  
 * Copyright: Copyright (corporation)2015  
 * Company: Corporation  
 * @version: 1.0  
 * Modification History:  
 * Modified by :   
 */
package com.base.framework.core.util;
import java.math.BigDecimal;
import java.util.HashMap;
import java.util.Map;

/**
 * 等额本息还款,也称定期付息,即借款人每月按相等的金额偿还贷款本息,其中每月贷款利息按月初剩余贷款本金计算并逐月结清。把按揭贷款的本金总额与利息总额相加,
 * 然后平均分摊到还款期限的每个月中。作为还款人,每个月还给银行固定金额,但每月还款额中的本金比重逐月递增、利息比重逐月递减。
 */

public class AverageCapitalPlusInterestUtils {

    /**
     * 等额本息计算获取还款方式为等额本息的每月偿还本金和利息
     * 
     * 公式:每月偿还本息=〔贷款本金×月利率×(1+月利率)^还款月数〕÷〔(1+月利率)^还款月数-1〕
     * 
     * @param invest
     *            总借款额(贷款本金)
     * @param yearRate
     *            年利率
     * @param month
     *            还款总月数
     * @return 每月偿还本金和利息,不四舍五入,直接截取小数点最后两位
     */
    public static BigDecimal getPerMonthPrincipalInterest(double invest, double yearRate, int totalmonth) {
        double monthRate = yearRate / 12;
        BigDecimal monthIncome = new BigDecimal(invest)
                .multiply(new BigDecimal(monthRate * Math.pow(1 + monthRate, totalmonth)))
                .divide(new BigDecimal(Math.pow(1 + monthRate, totalmonth) - 1), 2, BigDecimal.ROUND_UP);
        //return monthIncome.doubleValue();
        return monthIncome;
    }

    /**
     * 等额本息计算获取还款方式为等额本息的每月偿还利息
     * 
     * 公式:每月偿还利息=贷款本金×月利率×〔(1+月利率)^还款月数-(1+月利率)^(还款月序号-1)〕÷〔(1+月利率)^还款月数-1〕
     * 
     * @param invest
     *            总借款额(贷款本金)
     * @param yearRate
     *            年利率
     * @param month
     *            还款总月数
     * @return 每月偿还利息
     */
    public static Map getPerMonthInterest(double invest, double yearRate, int totalmonth) {
        Map map = new HashMap();
        double monthRate = yearRate / 12;
        BigDecimal monthInterest;
        for (int i = 1; i < totalmonth + 1; i++) {
            BigDecimal multiply = new BigDecimal(invest).multiply(new BigDecimal(monthRate));
            BigDecimal sub = new BigDecimal(Math.pow(1 + monthRate, totalmonth))
                    .subtract(new BigDecimal(Math.pow(1 + monthRate, i - 1)));
            monthInterest = multiply.multiply(sub).divide(new BigDecimal(Math.pow(1 + monthRate, totalmonth) - 1), 2,
                    BigDecimal.ROUND_DOWN);
            monthInterest = monthInterest.setScale(2, BigDecimal.ROUND_DOWN);
            map.put(i, monthInterest);
        }
        return map;
    }

    /**
     * 等额本息计算获取还款方式为等额本息的每月偿还本金
     * 
     * @param invest
     *            总借款额(贷款本金)
     * @param yearRate
     *            年利率
     * @param month
     *            还款总月数
     * @return 每月偿还本金
     */
    public static Map getPerMonthPrincipal(double invest, double yearRate, int totalmonth) {
        double monthRate = yearRate / 12;
        BigDecimal monthIncome = new BigDecimal(invest)
                .multiply(new BigDecimal(monthRate * Math.pow(1 + monthRate, totalmonth)))
                .divide(new BigDecimal(Math.pow(1 + monthRate, totalmonth) - 1), 2, BigDecimal.ROUND_DOWN);
        Map mapInterest = getPerMonthInterest(invest, yearRate, totalmonth);
        Map mapPrincipal = new HashMap();

        for (Map.Entry entry : mapInterest.entrySet()) {
            mapPrincipal.put(entry.getKey(), monthIncome.subtract(entry.getValue()));
        }
        return mapPrincipal;
    }

    /**
     * 等额本息计算获取还款方式为等额本息的总利息
     * 
     * @param invest
     *            总借款额(贷款本金)
     * @param yearRate
     *            年利率
     * @param month
     *            还款总月数
     * @return 总利息
     */
    public static double getInterestCount(double invest, double yearRate, int totalmonth) {
        BigDecimal count = new BigDecimal(0);
        Map mapInterest = getPerMonthInterest(invest, yearRate, totalmonth);

        for (Map.Entry entry : mapInterest.entrySet()) {
            count = count.add(entry.getValue());
        }
        return count.doubleValue();
    }

    /**
     * 应还本金总和
     * 
     * @param invest
     *            总借款额(贷款本金)
     * @param yearRate
     *            年利率
     * @param month
     *            还款总月数
     * @return 应还本金总和
     */
    public static double getPrincipalInterestCount(double invest, double yearRate, int totalmonth) {
        double monthRate = yearRate / 12;
        BigDecimal perMonthInterest = new BigDecimal(invest)
                .multiply(new BigDecimal(monthRate * Math.pow(1 + monthRate, totalmonth)))
                .divide(new BigDecimal(Math.pow(1 + monthRate, totalmonth) - 1), 2, BigDecimal.ROUND_DOWN);
        BigDecimal count = perMonthInterest.multiply(new BigDecimal(totalmonth));
        count = count.setScale(2, BigDecimal.ROUND_DOWN);
        return count.doubleValue();
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        double invest = 38988; // 本金
        int month = 12;
        double yearRate = 0.15; // 年利率
        BigDecimal perMonthPrincipalInterest = getPerMonthPrincipalInterest(invest, yearRate, month);
        System.out.println("等额本息---每月还款本息:" + perMonthPrincipalInterest);
        System.out.println("等额本息---每月还款本息:" + getPerMonthPrincipalInterest(invest, yearRate, 3));
        System.out.println("等额本息---每月还款本息:" + getPerMonthPrincipalInterest(invest, yearRate, 6));
        System.out.println("等额本息---每月还款本息:" + getPerMonthPrincipalInterest(invest, yearRate, 9));
        System.out.println("等额本息---每月还款本息:" + getPerMonthPrincipalInterest(invest, yearRate, 12));
        System.out.println("等额本息---每月还款本息:" + getPerMonthPrincipalInterest(invest, yearRate, 15));
        System.out.println("等额本息---每月还款本息:" + getPerMonthPrincipalInterest(invest, yearRate, 18));
        /*Map mapInterest = getPerMonthInterest(invest, yearRate, month);
        System.out.println("等额本息---每月还款利息:" + mapInterest);
        Map mapPrincipal = getPerMonthPrincipal(invest, yearRate, month);
        System.out.println("等额本息---每月还款本金:" + mapPrincipal);
        double count = getInterestCount(invest, yearRate, month);
        System.out.println("等额本息---总利息:" + count);
        double principalInterestCount = getPrincipalInterestCount(invest, yearRate, month);
        System.out.println("等额本息---应还本息总和:" + principalInterestCount);*/
    }
}

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