Array数组必须指定length

比如，

public class test{
   private String name;
   private String pwd;
   private String[] account=new String[3];
   public test(String a, String b,String c,String d,String f){
       name=a;
       pwd=b;
       account[0]=c;
       account[1]=d;
       account[2]=f;

       //这地方不报空指针才怪
       account[3]=f;
   }
   public static void main(String[] args){
       test newTest = new test("1","2","2","2","2"); 
       System.out.print(newTest.account[0]);
   }

}