java数组越界错误

package home_work_4_17;


abstract class Employee{
    abstract double  earnings();
}

class YearWorker extends Employee{
     double earnings(){
         System.out.println("按年领取1000");
         return 1000;
     }
}

class MonthWorker extends Employee{
     double earnings(){
         System.out.println("按月领取100");
         return 100;
     }
}

class WeekWorker extends Employee{
     double earnings(){
         System.out.println("按星期领取10");
         return 10;
     }
}

class Company{
    int n;    //该公司的人数
    public Company(int n) {
        this.n=n;// TODO Auto-generated constructor stub
    }
    Employee E[]=new Employee[n];
    
    double cal(){        //返回薪水综合
        double sum=0;
        for(int j=0;j<n;j++){
            sum+=E[j].earnings();
        }
        return sum;
    }
}
public class work_2 {
    public static void main(String args[]) {
        Company c=new Company(3);
        
        c.E[0]=new WeekWorker();
        c.E[1]=new MonthWorker();
        c.E[2]=new YearWorker();
        
        System.out.println("总支出："+c.cal());
    }
}

 编译器显示数组越界错误。

经检查发现划线部分语句出错

应当做如下修改：

 

class Company{
    int n;    //该公司的人数
     Employee E[]； 
    public Company(int n) {
        this.n=n;// TODO Auto-generated constructor stub
        E=new Employee[n];   
     }
   
    double cal(){        //返回薪水综合
        double sum=0;
        for(int j=0;j<n;j++){
            sum+=E[j].earnings();
        }
        return sum;
    }
}

出错原因是：当Company构造方法中并未对数组E进行初始化操作，故而E数组大小仍然为0，发生数组越界错误。

利用上述错误方式编写的测试程序如下：

package test_a;
class people{
    int n;
    Student s[]=new Student[n];
    public people(int n) {
        this.n=n;// TODO Auto-generated constructor stub
    }
    
}

class Student{
    int number;
}

public class Cdcs {
    public static void main(String args[]) {
        people p=new people(3);
        
        System.out.println(p.s.length);
    }
}

输出结果为0。即数组大小为零。