Java 正在尝试确定“中的array.length”；至于；使用变量时循环
我有一个名为“multiarray”的二维数组。第一个是[7]，第二个当前初始化为[500]。我正在从一个文本文件中读取数据，该文件的第二个数组中有随机数目的条目。数组永远不会有500个条目，我需要知道有多少条条目 我在想Java 正在尝试确定“中的array.length”；至于；使用变量时循环,java,arrays,Java,Arrays,我有一个名为“multiarray”的二维数组。第一个是[7]，第二个当前初始化为[500]。我正在从一个文本文件中读取数据，该文件的第二个数组中有随机数目的条目。数组永远不会有500个条目，我需要知道有多少条条目 我在想y
yimport java.io.File;
import java.io.FileNotFoundException;
import java.util.Formatter;
import java.util.Scanner;
public class DOW
{
public static void main(String[] args)
{
File file = new File ("/Users/***/RandomInts.txt") ;
try
{
Scanner scanner = new Scanner(file) ;
//Formatter formatter = new Formatter (new File ("outputfile.txt")) ;
int [][] multiarray = new int [7][500];
int counter1 = 0;
int counter2 = 0;
int counter3 = 0;
int counter4 = 0;
int counter5 = 0;
int counter6 = 0;
int counter7 = 0;
while (scanner.hasNext())
{
int dow = scanner.nextInt () ;
int temp = scanner.nextInt () ;
dow = dow -1;
if(dow == 0)
{
multiarray[dow][counter1] = temp;
counter1 ++;
}
if(dow == 1)
{
multiarray[dow][counter2] = temp;
counter2 ++;
}
if(dow == 2)
{
multiarray[dow][counter3] = temp;
counter3 ++;
}
if(dow == 3)
{
multiarray[dow][counter4] = temp;
counter4 ++;
}
if(dow == 4)
{
multiarray[dow][counter5] = temp;
counter5 ++;
}
if(dow == 5)
{
multiarray[dow][counter6] = temp;
counter6 ++;
}
if(dow == 6)
{
multiarray[dow][counter7] = temp;
counter7 ++;
}
}
for (int x = 0; x < 7; x++)
{
int hightemp = 0;
int lowtemp = 0;
int avetemp = 0;
for (int y = 0; y < multiarray[x].length ; y++)
{
if (multiarray[x][y] > hightemp)
{
hightemp = multiarray[x][y];
}
if (multiarray[x][y] < lowtemp)
{
lowtemp = multiarray[x][y];
}
avetemp = avetemp + multiarray[x][y];
}
//avetemp = avetemp /
}
//formatter.format (" %d %d \n " , dow , temp ) ;
//formatter.flush () ;
//formatter.close () ;
//int[] dow;
//dow = new int [7];
//int[] temp;
//temp = new int [100];
//int x = 0;
//while ( x < temp.length)
//{
//System.out.println (temp[x]);
//++x;
//temp[x]=0;
//}
}
catch (FileNotFoundException e)
{}
}
}
5 67
2 -15
1 -40
7 32
6 -24
7 33
5 -32
3 57
3 41
6 51
基本上，第一列是一周中的一天，第二列是一个温度。这段代码没有太大的错误，但是如果用长度500初始化y数组，那么不管实际填充了多少个元素，长度都会返回这个值。如果需要，请在读取文件后初始化数组，或者使用java.util.List。如果值不可能是0，那么您也可以迭代所有非0值，并在第一个0处停止。java中的数组是静态的，这意味着它已经预先分配了您声明的空间，因此，multiarray[y]。长度将始终为500，无论您实际插入了多少个条目。您都可以使用ArrayList或LinkedList。它们的空间都是动态分配的，因此它们的长度将告诉您它们实际包含多少个条目。数组具有固定大小-您正在将第二维度的数组初始化为500长度。在该数组上调用length将始终返回500。如果您想要更动态的数据结构，请考虑ArrayList。当您添加到它时，size（）返回的值将递增 如果不想切换到ArrayList，则可以将数组更改为三维数组，第三维数组的长度为1。这可能是保持第二维度大小的地方 -- 我不知道这是否是您的错误的原因，但您的代码中确实存在错误。最后的while循环尝试访问临时阵列外部：
int x = 0;
while (x < temp.length) {
System.out.println(temp[x]);
++x;
temp[x] = 0;
}
intx=0；
而（x<温度长度）{
系统输出打印LN（温度[x]）；
++x；
温度[x]=0；
}
for(x=0; x<temp.length; x++)
{
System.out.println(temp[x]);
temp[x] = 0;
}
for（x=0；x现在我知道您的输入是什么样子了
import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;
public class DOW {
public static void main(String[] args) {
File file = new File("/Users/***/RandomInts.txt");
try {
Scanner scanner = new Scanner(file);
ArrayList<Integer>[] multiarray = new ArrayList[7]; // This is how one would make an array of ArrayList's.
for (int i = 0; i < multiarray.length; i++)
multiarray[i] = new ArrayList<Integer>();
while (scanner.hasNextInt()) { //This is how you would save the values. You were saving temperatures incorrectly.
int dow = scanner.nextInt() - 1; //Get day of week.
int temp = scanner.nextInt(); //Get temperature. [Would throw exception here if your input was bad]
multiarray[dow].add(temp); //Store temperature in the array representing the day of week.
}
// Looks like you want to find min, max and average in each column here.
for (int x = 0; x < 7; x++) {
int hightemp = Integer.MIN_VALUE; // Set this to something really low. (You will see why in a minute)
int lowtemp = Integer.MAX_VALUE; // Set this to something really high.
double avetemp = 0; // You seem to be using ave as "sum" right now and then you plan on dividing which is fine. This should also be a double.
int size = multiarray[x].size(); // No point calling .size() [or in general any function] over and over again. Its better to just cache the answer.
for (int y = 0; y < size; y++) {
int num = multiarray[x].get(y); // Same logic as size here.
hightemp = Math.max(hightemp, num);
lowtemp = Math.min(lowtemp, num);
avetemp += num;
}
avetemp = avetemp / size;
// P.S.: Also you probably want to save the values of hightemp, lowtemp, avetemp somewhere after doing all this work!
// Removed the rest of your code as it is irrelevant for your question.
}
// Close your streams.
scanner.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (Exception e) {
// This would happen if your input file is bad.
e.printStackTrace();
}
}
}
导入java.io.File；
导入java.io.FileNotFoundException；
导入java.util.ArrayList；
导入java.util.Scanner；
公共类道指{
公共静态void main（字符串[]args）{
File File=新文件（“/Users/***/RandomInts.txt”）；
试一试{
扫描仪=新扫描仪（文件）；
ArrayList[]multiarray=new ArrayList[7]；//这就是如何创建ArrayList的数组。
对于（int i=0；i
编辑：您添加的内容正确。我的不好。使用ArrayList.ArrayList#size（）我看不到您将任何内容放入数组中。我们需要查看您从文件中读取的代码，并将内容放入数组中。我会在这里使用所有答案，并使用ArrayList或LinkedList，但如果您确实必须使用基本数组，则可以使用Integer
boxed类型。您只需计算所有数组中的非空整数以获取数据长度（数组长度仍将为500）。是的，好吧，这一切都错了。请在一分钟内检查我的编辑。我本来希望，尽管我已将其初始化为500。长度只会给我多少个元素（？）已添加。我将仔细查看arraylist，因为我需要对未知数量的条目进行此操作。我应该对该区域进行注释。我还没有调试到那个程度，我将重点关注“for”关于这一点的部分。我现在将编辑代码。这很好，它做了我需要它做的事情。我显然还有很多工作要做，但很欣赏解释代码的示例和注释。
import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;
public class DOW {
public static void main(String[] args) {
File file = new File("/Users/***/RandomInts.txt");
try {
Scanner scanner = new Scanner(file);
ArrayList<Integer>[] multiarray = new ArrayList[7]; // This is how one would make an array of ArrayList's.
for (int i = 0; i < multiarray.length; i++)
multiarray[i] = new ArrayList<Integer>();
while (scanner.hasNextInt()) { //This is how you would save the values. You were saving temperatures incorrectly.
int dow = scanner.nextInt() - 1; //Get day of week.
int temp = scanner.nextInt(); //Get temperature. [Would throw exception here if your input was bad]
multiarray[dow].add(temp); //Store temperature in the array representing the day of week.
}
// Looks like you want to find min, max and average in each column here.
for (int x = 0; x < 7; x++) {
int hightemp = Integer.MIN_VALUE; // Set this to something really low. (You will see why in a minute)
int lowtemp = Integer.MAX_VALUE; // Set this to something really high.
double avetemp = 0; // You seem to be using ave as "sum" right now and then you plan on dividing which is fine. This should also be a double.
int size = multiarray[x].size(); // No point calling .size() [or in general any function] over and over again. Its better to just cache the answer.
for (int y = 0; y < size; y++) {
int num = multiarray[x].get(y); // Same logic as size here.
hightemp = Math.max(hightemp, num);
lowtemp = Math.min(lowtemp, num);
avetemp += num;
}
avetemp = avetemp / size;
// P.S.: Also you probably want to save the values of hightemp, lowtemp, avetemp somewhere after doing all this work!
// Removed the rest of your code as it is irrelevant for your question.
}
// Close your streams.
scanner.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (Exception e) {
// This would happen if your input file is bad.
e.printStackTrace();
}
}
}