Java定积分计算

1. 运用了Javalambda表达式
2. 简单版本，仅供参考

import java.util.function.UnaryOperator;

public class DefiniteIntegral {
    /**
     * 函数
     */
    private UnaryOperator<Double> function;
    /**
     * 积分的范围
     */
    private DoubleRange range;
    /**
     * 积分的精度
     */
    private int precision;

    public DefiniteIntegral(UnaryOperator<Double> function, DoubleRange range, int precision) {
        this.function = function;
        this.range = range;
        this.precision = precision;
    }

    public static DefiniteIntegral create(UnaryOperator<Double> function, DoubleRange range, int precision) {
        return new DefiniteIntegral(function, range, precision);
    }

    /**
     * 得到设定的函数的值
     * @param x 给定参数
     * @return 函数的值
     */
    private Double getFunctionVal(double x) {
        return function.apply(x);
    }

    /**
     * 得到△X的值
     * @return 每个区间的大小, 即△X的值
     */
    private double getEachSize() {
        return range.getRange() / precision;
    }

    /**
     * 得到一个区间之间的X轴上的随机点
     * @param val 区间的左端点
     * @return 一个区间之间的X轴上的随机点
     */
    private double getξ(double val) {
        return ((2 * val) + getEachSize()) / 2;
    }

    /**
     * 计算定积分
     * @return 给定函数的定积分
     */
    public double calculateArea() {
        double result = 0.0;
        double eachSize = getEachSize();

        for (double i = range.getStart(); i < range.getEnd(); i += eachSize) {
            result += eachSize * getFunctionVal(getξ(i));
        }

        return result;
    }

    public static void main(String[] args) {
    	// 需要求积分的函数可以随意改变
        UnaryOperator<Double> function = x -> x + 1;
        // 积分的范围
        DoubleRange range = DoubleRange.create(5, 9);
        // 积分的精度
        int precision = 10000;
        DefiniteIntegral functionArea = DefiniteIntegral.create(function, range, precision);

        System.out.println(functionArea.calculateArea());
    }

    private static class DoubleRange{
        private double start;
        private double end;

        public static DoubleRange create(double start, double end) {
            return new DoubleRange(start, end);
        }

        public DoubleRange(double start, double end) {
            this.start = start;
            this.end = end;
        }

        public double getRange() {
            return end - start;
        }

        public double getStart() {
            return start;
        }

        public double getEnd() {
            return end;
        }
    }
}