案例分析：运用身体质量指数（BMI）衡量人体胖瘦程度

问题：运用BMI及相关参考标准（Tab1.1），衡量人体胖瘦程度。

思路：

Step 1 ：表格拆解（明确各分段函数）

Step  2：构造关系节点（Mapping）

package bmi;
/**
 * @see 关系节点
 * @author JustBeGeek
 */
public class Mapping{
        private int gradation;
        private String degree;
        public Mapping(int gradation,String degree){
            this.gradation=gradation;
            this.degree=degree;
        }
        public int  getGradation(){
            return gradation;
        }
        public  String getGrade(){
            return degree;
        }      
    }

Step 3 ：存储各参考标准（构造分段函数）

/**
     * @see 参考标准集
     */
    /*世卫组织参考标准*/
    public static final Mapping[] WHO_RS={
        new Mapping(0,"偏瘦"), new Mapping(18.5,"正常"),
        new Mapping(25,"偏胖"), new Mapping(30,"肥胖Ⅰ"),
        new Mapping(35,"肥胖Ⅱ"), new Mapping(40,"肥胖Ⅲ")
    };
    /*亚洲参考标准*/
    public static final Mapping[] Asia_RS={
        new Mapping(0,"偏瘦"), new Mapping(18.5,"正常"),
        new Mapping(23,"偏胖"), new Mapping(25,"肥胖Ⅰ"),
        new Mapping(30,"肥胖Ⅱ"), new Mapping(40,"肥胖Ⅲ")  
    };
    /*中国参考标准*/
    public static final Mapping[] China_RS={
        new Mapping(0,"偏瘦"), new Mapping(18.5,"正常"),
        new Mapping(24,"偏胖"), new Mapping(28,"肥胖"),
        new Mapping(40,"极度肥胖")
    };

注：每个关系节点的分界值域存储 对应BMI范围的下界。

Step 4 ：BMI计算

/**
     * @see 计算BMI
     * @param weight  体重（kg）
     * @param height  身高（m）
     * @return 
     */
    public static double compute_BMI(double weight,double height){
        return (int)(weight/Math.pow(height, 2)*100)/100.0;
    }

Step 5：编写BMI评价函数（函数求值）

 /**
     * @see BMI评价
     * @param rs  参考标准
     * @param bmi 身体质量指数
     * @return 
     */
    public static String evaluate_BMI(Mapping[] rs,double bmi){
        int i=rs.length-1;
        for(;i>=0;i--){
            if(bmi>=rs[i].getGradation())
                break;
        }     
        return rs[i].getDegree();
    }

Step  6：集成并运行评价程序

package bmi;
import java.util.Scanner;
import bmi.ReferenceStandard;
/**
 * @see BMI评价集成程序
 * @author JustBeGeek
 */
public class Evaluate {
    public  static void main(String[] args){
        Scanner input=new Scanner(System.in);
        System.out.println("请输入您的体重（kg）：");
        double weight=input.nextDouble();
        System.out.println("请输入您的身高（m）：");
        double height=input.nextDouble();
        double bmi=ReferenceStandard.compute_BMI(weight, height);
        String degree=ReferenceStandard.evaluate_BMI(ReferenceStandard.Asia_RS, bmi);
        System.out.println("您的身体"+degree);
    }
}

相关类完整代码（实现）：

package bmi;
import bmi.Mapping;
/**
 * @see 参考标准
 * @author JustBeGeek
 */
public class ReferenceStandard {
    /**
     * @see 参考标准集
     */
    /*世卫组织参考标准*/
    public static final Mapping[] WHO_RS={
        new Mapping(0,"偏瘦"), new Mapping(18.5,"正常"),
        new Mapping(25,"偏胖"), new Mapping(30,"肥胖Ⅰ"),
        new Mapping(35,"肥胖Ⅱ"), new Mapping(40,"肥胖Ⅲ")
    };
    /*亚洲参考标准*/
    public static final Mapping[] Asia_RS={
        new Mapping(0,"偏瘦"), new Mapping(18.5,"正常"),
        new Mapping(23,"偏胖"), new Mapping(25,"肥胖Ⅰ"),
        new Mapping(30,"肥胖Ⅱ"), new Mapping(40,"肥胖Ⅲ")  
    };
    /*中国参考标准*/
    public static final Mapping[] China_RS={
        new Mapping(0,"偏瘦"), new Mapping(18.5,"正常"),
        new Mapping(24,"偏胖"), new Mapping(28,"肥胖"),
        new Mapping(40,"极度肥胖")
    };
    /**
     * @see 计算BMI
     * @param weight  体重（kg）
     * @param height  身高（m）
     * @return 
     */
    public static double compute_BMI(double weight,double height){
        return (int)(weight/Math.pow(height, 2)*100)/100.0;
    }
    /**
     * @see BMI评价
     * @param rs  参考标准
     * @param bmi 身体质量指数
     * @return 
     */
    public static String evaluate_BMI(Mapping[] rs,double bmi){
        int i=rs.length-1;
        for(;i>=0;i++){
            if(bmi>=rs[i].getGradation())
                break;
        }     
        return rs[i].getDegree();
    }
}

package bmi;
/**
 * @see 关系节点
 * @author JustBeGeek
 */
public class Mapping{
        private double gradation;
        private String degree;
        public Mapping(double gradation,String degree){
            this.gradation=gradation;
            this.degree=degree;
        }
        public double  getGradation(){
            return gradation;
        }
        public  String getDegree(){
            return degree;
        }      
    }

为什么这么做？可参考   案例分析：百分制转等级制程序演进