创建双数组列表的问题 [英] issue creating a double array list

问题描述

空闲代码是否有任何原因会导致编译错误?

Is there any reason the fallowing code would give A compile error ?

Import java.util.*;

public class Storageclass
// class used to store the Student data 
{
 // creates the private array list needed. 
 private ArrayList<String> nameList = new ArrayList<String>();
 private ArrayList<double> GPAList = new ArrayList<double>();
 private ArrayList<double> passedList = new ArrayList<double>();
}

这是在主文件的类访问中，该类中有更多内容不是此错误的一部分.当我运行这个时，两个 double arrayList 给了我这个错误.

this is in a class access by a main file there is more in the class by it not part of this error. when I run this the two double arrayList give me this error.

Storageclass.java:8: error: unexpected type
 private ArrayList<double> GPAList = new ArrayList<double>(1);
                   ^
  required: reference
  found:    double

我不确定为什么或该错误意味着什么，我们将不胜感激.

I am not sure why or what that error means any help would be appreciated.

~感谢您的帮助是我犯的一个令人尴尬的新手错误，但希望这可以帮助其他人.

~ Thanks for the help was a embarrassingly novice mistake I made, but hope full this can help some other person.

推荐答案

由于所有泛型类型 都是 在运行时擦除到 Object 代替 T 的每种类型也必须扩展目的.所以你不能将 T 设置为像 double 这样的原始类型，但你可以使用它的包装类 Double.试试这个方法:

Since all generic types <T> are erased at runtime to Object every type you put in place of T must also extend Object. So you can't set T to be primitive type like double but you can use its wrapper class Double. Try this way:

private List<Double> passedList = new ArrayList<Double>();

或者从 Java7 开始的更短的版本

or since Java7 little shorter version

private List<Double> passedList = new ArrayList<>();

如果您尝试将 double 类型的 add 变量添加到这样的数组中，也不要担心，因为它将是 自动装箱到Double.

Also don't worry if you try to add variable of double type to such array since it will be autoboxed to Double.

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