关于自建的类建立数组的问题

Question

package sort;

public class WorkArea {
private double random;
private int rnum;
public void setRandom(double ran){
this.random=ran;
}
public double getRandom(){
return random;
}
public void setRnum(int rnum){
this.rnum=rnum;
}
public int getRnum(){
return rnum;
}
public static void main(String[] args){
WorkArea[] wa=new WorkArea[100];
double[] dou=new FileOpt().filIn();
for(int i=0;i<wa.length;i++){
[color=red]wa[i].setRandom(dou[i]);[/color]
}
}
}
程序如上，红色字体部分为什么会抛出异常？

Answer 1

[quote]wa[i].setRandom(dou[i]); [/quote]
wa[i]是null，所以会抛出空指针异常[quote]for(int i=0;i<wa.length;i++){
wa[i].setRandom(dou[i]);
} [/quote]
改成
for(int i=0;i<wa.length;i++){
wa[i]=new WorkArea();
wa[i].setRandom(dou[i]);
}