使用Function Interface简化if-else代码示例

使用表驱动的方法，利用Function Interface优化If-else的示例代码：

package com.siasun.java8.function.function;

import java.math.BigDecimal;
import java.util.List;
import java.util.function.Function;

/**
 * 税金计算
 * Function Interface 简化 if-else判断示例
 * @author : wanggang
 * @create 2025/7/15 8:21
 */
public class TaxCalculateDemo {

  //定义计算表达式
  public static List<RangeHandler> calculateTaxHandlers = List.of(
    new RangeHandler(
      null,
      new BigDecimal(36000),
      d -> d.multiply(new BigDecimal("0.1"))
    ),
    new RangeHandler(
      new BigDecimal(36000),
      new BigDecimal(144000),
      d -> d.multiply(new BigDecimal("0.2"))
    ),
    new RangeHandler(
      new BigDecimal(14000),
      null,
      d -> d.multiply(new BigDecimal("0.3"))
    )
  );

  public static void main(String[] args) {
    BigDecimal yearIncome = new BigDecimal(36001);

    BigDecimal tax = calculateTaxHandlers
      .stream()
      .filter(d -> d.matches(yearIncome))
      .findFirst()
      .map(handler -> handler.execute(yearIncome))
      .orElse(new BigDecimal(0));

    System.out.println("个人所得税为：" + tax);
  }

  public static class RangeHandler {

    private final BigDecimal min;
    private final BigDecimal max;
    private final Function<BigDecimal, BigDecimal> action;

    public RangeHandler(
      BigDecimal min,
      BigDecimal max,
      Function<BigDecimal, BigDecimal> action
    ) {
      this.min = min;
      this.max = max;
      this.action = action;
    }

    public boolean matches(BigDecimal value) {
      boolean flag = true;
      if (min != null) {
        flag = value.compareTo(min) >= 0;
      }
      if (max != null) {
        flag = flag && value.compareTo(max) < 0;
      }
      return flag;
    }

    public BigDecimal execute(BigDecimal value) {
      return action.apply(value);
    }
  }
}