请问为什么这段代码什么也运行不出来呢？

Question

package com.company;

public class Main {

    public static void main(String[] args) {
        CircleWithPrivateDataFields[] circleArray;
        circleArray = createCircleArray();
    }
    public static CircleWithPrivateDataFields[] createCircleArray() {
        CircleWithPrivateDataFields[] circleArray = new CircleWithPrivateDataFields[5];
        for (int i = 0; i < circleArray.length; i++) {
            circleArray[i] = new CircleWithPrivateDataFields(Math.random() * 10);
        }
        return circleArray;
    }
    public static void printCircleArray(CircleWithPrivateDataFields[] circleArray){
        System.out.printf("%-30s%-15s\n","Radius","Area");
        for (int i = 0 ; i < circleArray.length ; i++){
            System.out.printf("%-30s%-15s\n",circleArray[i].getRadius(),circleArray[i].getArea());
        }
        System.out.println("----------------------------------");
        System.out.printf("%-30s%-15s\n","The total circles is",sum(circleArray));
    }
    public static double sum(CircleWithPrivateDataFields[] circleArray){
        double sum = 0;
        for(int j = 0 ; j < circleArray.length ; j++){
            sum += circleArray[j].getArea();
        }
        return sum;
    }
}
class CircleWithPrivateDataFields{
    private double radius = 1;
    private static  int numberOfSubjects = 0;
    public CircleWithPrivateDataFields(){
        numberOfSubjects++;
    }
    public CircleWithPrivateDataFields(double newRadius){
        radius = newRadius;
        numberOfSubjects++;
    }

    public double getRadius() {
        return radius;
    }

    public void setRadius(double newRadius) {
        radius = (newRadius >= 0 )?newRadius:0;
    }

    public static int getNumberOfSubjects() {
        return numberOfSubjects;
    }
    public double getArea(){
        return radius * radius * Math.PI;
    }
}

这是《Java语言程序设计基础篇》P298的例题

拜托大神帮忙看看。

Answer 1

mian方法中这样写：

public static void main(String[] args) {
    CircleWithPrivateDataFields[] circleArray;
    circleArray = createCircleArray();
    // 调用输出方法
    printCircleArray(circleArray);
}

这样就将运行的结果输出到控制台了

可以在main方法中输入一条打印语句

System.out.println("circleArray: length = "+ circleArray.length);