英文:
How to add elements to an object list in java
问题
public class Bus{
private int seats;
private List<People> currentPeople;
public Bus(int seats){
this.seats = seats;
}
public void passengers(List<People> boarders, List<People> deboarders){
this.currentPeople.remove(deboarders);
this.currentPeople.add(boarders);
}
}
我试图创建一个乘客列表在公共汽车上。我试图从列表中移除下车的乘客，并添加上车的乘客。但是Java不允许我将上车的乘客添加到currentPeople列表中。People是一个存储乘客姓名和票号的类。对此有任何帮助吗？我已经尝试解决了几个小时。
<details>
<summary>英文:</summary>
public class Bus{
private int seats;
private List<People> currentPeople;
public Bus(int seats){
this.seats = seats;
}
public void passengers(List<People> boarders, List<People> deboarders){
this.currentPeople.remove(deboarders);
this.currentPeople.add(boarders);
}
I'm trying to create a list of people on the bus. I'm trying to remove deboarders(alighting passengers) from the list and add the boarders(boarding passengers). But Java won't let me add the boarders to the currentPeople list. People is a class which stores the name and ticket number of the passanger. Any help on this? I've been trying to solve this for hours.
</details>
# 答案1
**得分**: 3
添加一组对象到列表中，你需要使用 `addAll` 方法：
```java
this.currentPeople.addAll(boarders);
从列表中移除一组对象，你需要使用 removeAll 方法：
this.currentPeople.removeAll(deboarders);
注意，为了比较并从列表中移除正确的元素，removeAll 方法使用了 equals 方法。因此，你应该在你的 People 类中实现 equals 方法。
编辑：
People 类的 equals 方法：
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
People people = (People) o;
if (ticketNumber != people.ticketNumber) return false;
return name != null ? name.equals(people.name) : people.name == null;
}
别忘了初始化 currentPeople 列表，否则会出现 NullPointerException。
英文:
To add a collection of objects to a list you need to use addAll:
this.currentPeople.addAll(boarders);
To remove a collection of objects from a list you need to use removeAll:
this.currentPeople.removeAll(deboarders);
Be careful, in order to compare and remove the right elements from the list, removeAll uses equals method. So you should implement equals method in your People class.
EDIT:
equals method for People class:
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
People people = (People) o;
if (ticketNumber != people.ticketNumber) return false;
return name != null ? name.equals(people.name) : people.name == null;
}
Don't forget to initialize currentPeople list, otherwise you will get NullPointerException.
答案2
得分: 0
将"add"更改为"addAll"，"remove"同样如此。正如Federico在评论中指出的那样，前提是"People"类已实现了equals方法。
英文:
Change add to addAll and likewise for remove.
As Federico points out in comments, assuming People has equals method implemented.
答案3
得分: 0
尝试使用 removeAll() 和 addAll() 方法，因为您正在将一个集合作为参数传递。
不要忘记在构造函数内部的行末添加“;”。
this.currentPeople.removeAll(deboarders);
this.currentPeople.addAll(boarders);
英文:
Try removeAll() and addAll() methods because you are passing a Collection as a parameter.
Do not forget " ; " at the end of the line inside your constructor.
this.currentPeople.removeAll(deboarders);
this.currentPeople.addAll(boarders);
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