Java 数组实例化
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Array Instantiation
提问by user228390
Can you help me out with this question please.
你能帮我解决这个问题吗？
Question: Given the following array declarations
问题：给定以下数组声明
double readings[];
String urls[];
TicketMachine[] machines;
write assignments that accomplish the following tasks:
编写完成以下任务的作业：
- make the
readingsvariable refer to an array that is able to hold sixtydoublevalues - make the
urlsvariable refer to an array that is able to hold ninetyStringobjects - make the
machinesvariable refer to an array that is able to hold fiveTicketMachineobjects
- 使
readings变量引用一个能够容纳六十个double值的数组 - 使
urls变量指向一个能够容纳九十个String对象的数组 - 使
machines变量引用一个能够容纳五个TicketMachine对象的数组
My answer:
我的答案：
//declare and instantiate object
double readings [] = new double [60];
String urls [] = new String [90];
TicketMachine machines [] = new TicketMachine [5];
The error I am getting is this:
我得到的错误是这样的：
Main.java:16: readings is already defined in main(java.lang.String[])
double readings [] = new double [60];
^
Main.java:17: urls is already defined in main(java.lang.String[])
String urls [] = new String [90];
^
Main.java:18: machines is already defined in main(java.lang.String[])
TicketMachine machines [] = new TicketMachine [5];
采纳答案by John Feminella
Once you declare the variables, you don't need to mention their type again on future assignments.
一旦你声明了变量，你就不需要在以后的赋值中再次提及它们的类型。
Thus, if you do:
因此，如果你这样做：
int i;
int i = 5;
then you've redeclared the type of i, which is an error. Instead, just do:
那么您重新声明了 的类型i，这是一个错误。相反，只需执行以下操作：
int i;
i = 5;
Or even better, you can combine the two into one statement:
或者更好的是，您可以将两者合并为一个语句：
int i = 5;
Since the variables in your particular example have already been declared as a particular type, then you can just do:
由于您的特定示例中的变量已被声明为特定类型，因此您可以执行以下操作：
readings = ...;
urls = ...;
machines = ...;
回答by mportiz08
you've already declared those variables, so now you can just instantiate them
你已经声明了这些变量，所以现在你可以实例化它们
readings = new double[60];
urls = new String[90];
machines = new TicketMachine[5];
