小编sai*_*oms的帖子

我构建了一个具有此方法的程序,我还想计算我创建的对象数.但是在运行程序之后.它说有0个对象被创建.谁能知道为什么这不正确？应该说有4个对象正在创建.这是我的代码:

    /**
     This program implements code for a Circle class,
     which has a radius field, set and
     get methods, and a getArea method.
     Author: Michael Wu.
    */

    public class Circle
    {
        private double radius;
        private static int numCircles;

        public Circle(double radius)
        {
            this.radius = radius;
        }

        //SetRadius method,sets radius.
        public void setRadius(double radius)
        {
            this.radius = radius;
        }

        //GetRadius method; returns radius.
        public double getRadius()
        {
            return radius;
        }

        //Constructor increments numbers of circles.
        public Circle()
        {
            numCircles++;
        }

        //Copy …

我尝试使用一个简单的java EnumMap来存储道路类型到默认速度的映射.但是我立即遇到了以下问题:

我创建了一个简单的枚举如下:

   public enum RoadCategory {

        AUTOBAHN("Autobahn", 0),
        BUNDESSTR("Bundesstrasse", 1),
        OTHER("other", -1);

        private String name;
        private int code;

        private RoadCategory(String name, int code){
            this.name = name;
            this.code = code;
        }
    }

接下来,我创建了一个小类,试图将此枚举用作枚举映射的键:

import java.util.EnumMap;
import java.util.Map;

public class VehicleConfig {

    public static void main(String[] args) throws Exception {
        VehicleConfig v = new VehicleConfig();
        v.addSpeedMapping(RoadCategory.AUTOBAHN, 80.0);
    }

    private Map<RoadCategory,Double> speedMap;

    public VehicleConfig(){
        this.speedMap = new EnumMap<RoadCategory, Double>(RoadCategory.class);
    }

    public double addSpeedMapping(RoadCategory category, double speed) throws Exception{
        if(speedMap == null) …