java - 如何向对象类添加信息？

Question

class Client{
String name;

Client(String name){
this.name=name;
}

Client (){
name=null;
}
}

class Cashier{

LinkedList <Client> cashierclients;


Cashier(LinkedList<Client> cashierclients){
this.cashierclients=cashierclients;
}
Cashier(){
//this.cashierclients=null;
}

}
class test{
public static void main(String args []){

LinkedList<Client> l=new LinkedList<Client>();

//i do some scans here to add the names of persons to the LinkedList l                   

Cashier [] cashier=new Cashier[numberofcashiers];

for(int i=0;i<numberofcashiers; i++){
    cashier[i]=new Cashier();
}

现在我想向收银员添加一个客户[0]，我这样做:

cashier[0].cashierclients.addLast(l.get(0));

一切正常，但是当我想打印出纳员[1]的大小时，它返回1，但它应该返回0，因为我没有向出纳员[1]添加任何人。关于哪里出了问题有什么想法吗？

// the error happens here
cashier[1].cashierclients.size();

Answer 1

程序现在正在运行，它显示 cashier[1] 大小中的错误，应返回 0 而不是 1

import java.util.*;
class Client {
String name;

Client(String name) {
    this.name = name;
}

Client() {
    name = null;
}
}

class Cashier {

LinkedList<Client> cashierclients;


Cashier(LinkedList<Client> cashierclients) {
    this.cashierclients = cashierclients;
}

Cashier() {
//this.cashierclients=null;
}

}

public class test {
 public static void main(String args[]) {

    LinkedList<Client> l = new LinkedList<Client>();

// i created this LinkedList to solve the  nullpointerexception error

LinkedList<Client> empty =new LinkedList<Client>();

Client client1=new Client("Person1");
l.addLast(client1);

    Cashier[] cashier = new Cashier[10];

    for (int i = 0; i < 10; i++) {
        cashier[i] = new Cashier();
    }

// i did this to solve the  nullpointerexception error

for(int i=0; i<10; i++){
    cashier[i].cashierclients=empty;
}

cashier[0].cashierclients.addLast(l.get(0));

System.out.println(cashier[1].cashierclients.size());
//this should return zero
System.out.println(cashier[1].cashierclients.size());

}
}