英文:
Java converts long to int
问题
以下是要翻译的代码部分：
import java.util.*;
public class HelloWorld {
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
long N = s.nextLong();
long[] arr = new long[N];
System.out.println(N);
}
}
获取到以下错误信息：
HelloWorld.java:12: error: incompatible types: possible lossy conversion from long to int long[] arr = new long[N];
根据我理解，代码中没有涉及到int类型，有人能解释为什么会出现这个错误以及如何解决这个问题吗？
英文:
The following code:
import java.util.*;
public class HelloWorld{
public static void main(String []args){
Scanner s = new Scanner(System.in);
long N = s.nextLong();
long[] arr = new long[N];
System.out.println(N);
}
}
Getting this error:
HelloWorld.java:12: error: incompatible types: possible lossy conversion from long to int long[] arr = new long[N];
As far as I understand there is no int involved in the code, can anyone explain why this is happening and how to solve this issue?
答案1
得分: 3
在Java中，数组的大小不能超过int的范围，因此数组创建的大小参数隐式地是一个int。将N改为一个int。
来自JLS 15.10.1数组创建表达式（重点在于）：
每个维度表达式都会经历一次一元数值提升（§5.6.1）。提升的类型必须是
int，否则会导致编译时错误。
英文:
The size of arrays in Java can not exceed the range of an int, so the size parameter for array creation is implicitly an int. Change N to an int.
From JLS 15.10.1 Array Creation Expression (emphasis mine):
> Each dimension expression undergoes unary numeric promotion (§5.6.1). The promoted type must be int, or a compile-time error occurs.
答案2
得分: 2
Array subscripts and sizes in Java must always be int, so in this expression new long[N] the N is converted to int, and because long has a wider range than int, it's a narrowing conversion which must be done explicitly: new long[(int) N]. Or just read N as int: int N = s.nextInt().
英文:
Array subscripts and sizes in Java must always be int, so in this expression new long[N] the N is converted to int, and because long has wider range than int, it's a narrowing conversion which must be done explicitly: new long[(int) N]. Or just read N as int: int N = s.nextInt().
答案3
得分: 1
在这一行中，你正在创建一个大小为N的数组，但在Java中，数组的大小只能是整数，这就是为什么它将N视为一个整数。如果你的意图是创建一个大小为N的数组，你应该将N读取为一个整数。
int N = s.nextInt();
英文:
long[] arr = new long[N];
In this line you are creating an array of size N, but array sizes in Java can only be integers, that's why it's reading N as an int, if your intent is creating an array of N size you should read N as an int
int N = s.nextInt();
答案4
得分: 0
在Java中，数组的最大长度是2,147,483,647（2^31 - 1），这是int的最大长度。因此，数组最大可以容纳int的最大值，无法接受长整型数。
英文:
The maximum length of an array in java is 2,147,483,647 (2^31 - 1) which is the maximum length of int. So implicitly an array can have maximum the value of an int. So it cannot accept a long number.
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