java - 将整数存储在数组中后打印文件中的整数数量？

Question

我必须将文件中的所有整数存储到一个数组中，然后打印该数组和文件中的整数数量。

这里是在数组中存储整数的方法。它工作正常，因为我的第二个方法中的输出正确打印了 index = i, element = array[i] 。

public static Integer [ ] returnFileIntegers(String filename) {
  int i = 0;
  int x = 0;
  Integer [ ] array = new Integer[10000]; //instantiate array of 10000 integers
  if(filename.length() == 0){
     System.out.println("Please enter the file name as the 1st commandline argument.");
  }
  else {   //attempt connect and read file 
     File file = new File(filename);
     Scanner inputFromFile = null;
     try {
        inputFromFile = new Scanner(file);
     } 
     catch (FileNotFoundException fnfe) {
        System.out.print("ERROR: File not found for \"");
        System.out.println(filename+"\"");
     }        
     //if made connection to file, read file
     if(inputFromFile != null){         
        System.out.print("Reading from file \"" + filename + "\":\n");
        //loop and print to check if file connected

        //read next integer and store into array
        while (inputFromFile.hasNextLine()) {
           try {
              x = inputFromFile.nextInt();
              array[i] = x;
              i++;
              System.out.println(x);

           } 
           catch (InputMismatchException ime) {
              inputFromFile.next();
           }
           catch (NoSuchElementException nsee) {
           }
        }   
     }
  }
  return array;
}

这是我用来打印数组和整数数量的方法。我知道这是错误的，因为我正在打印 array.length 但我不知道应该使用什么来使其打印 整数数量 而不是 数组长度。

  public static void printArrayIndexInteger(Integer [ ] array, String filename) {
  //print number of integer in file
  System.out.println("Number of integers in file \"" + filename + "\" = " + array.length);
  //print array index and elements
  for(int i=0;i<array.length;i++) {
     if(array[i] != null){
     System.out.print("\nindex = " + i + ", ");
     System.out.print("element = " + array[i]);
     }
  }
}

这是当前输出的样子:

Number of integers in file "groceries.csv" = 10000

index = 0, element = 3
index = 1, element = 12
index = 2, element = 1
index = 3, element = 1
index = 4, element = 5
index = 5, element = 1

它应该是什么:

Number of integers in file "groceries.csv" = 6

index = 0, element = 3
index = 1, element = 12
index = 2, element = 1
index = 3, element = 1
index = 4, element = 5
index = 5, element = 1

如何获得打印数组中元素数量而不是数组长度的方法？

Answer 1

它说 10000 因为这就是你声明它的方式:

整数[]数组=新整数[10000]

这些额外的索引仍然存在，并且默认值为 null。数组长度等于数组中元素的数量。如果您事先不知道大小，请考虑使用大小可以调整的 ArrayList。

了解数组中有多少数字的唯一方法是循环遍历数组并进行计数，但是 ArrayList 比为数组分配任意大的长度是更好的解决方案。