分配新陣列時ArrayIndexOutOfBoundsException

Question

我想將一個數組排序到兩個其他數組必須是精確的長度。爲什麼在運行時出現錯誤Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 2 at Tal.main(Tal.java:39)？我知道有更好的方法來解決這個任務，但我不被允許。我必須這樣做。

public static void main(String[] args) 
{ 
    Scanner in = new Scanner(System.in); 

    System.out.print("How many random numbers from 0 to 999? "); 
    int amount = in.nextInt(); 

    int lowerCounter = 0; 
    int higherCounter = 0; 
    int[] numbers = new int[amount]; 
    System.out.print("Here is the random numbers: "); 
    for (int i = 0; i < numbers.length; i++) 
    { 
     numbers[i] = (int) Math.floor(Math.random()*1000); 
     System.out.print(numbers[i] + " "); 

     if (numbers[i] <= 499) { 
      lowerCounter++; 
     } 
     else { 
      higherCounter++; 
     } 
    } 
    System.out.println(""); 


    int[] numbersLow = new int[lowerCounter]; 
    int[] numbersHigh = new int[higherCounter]; 
    for(int i = 0; i < numbers.length; i++) 
    { 
     if (numbers[i] <= 499) 
     { 
      numbersLow[i] = numbers[i]; 
     } else { 
      numbersHigh[i] = numbers[i]; 
     } 
    } 

    System.out.print("These "+ lowerCounter +" numbers are from 0 to 499: "); 
    for(int i = 0; i < numbersLow.length; i++) 
    { 
     System.out.print(numbersLow[i] + " "); 
    } 

    System.out.println(""); 

    System.out.print("These "+ higherCounter +" numbers are from 500 to 999: "); 
    for(int i = 0; i < numbersHigh.length; i++) 
    { 
     System.out.print(numbersHigh[i] + " "); 
    } 

} 

Answer 1

您的循環變量不正確。你應該修正你的代碼，以便爲兩個數組和一個計數器有兩個不同的計數器來循環主數據。

lowerCounter=higherCounter=0; 
for(int i = 0; i < numbers.length; i++) { 
    if (numbers[i] <= 499) { 
     numbersLow[lowerCounter++] = numbers[i]; 
    } else { 
     numbersHigh[higherCounter++] = numbers[i]; 
    } 
} 

Answer 2

最好的辦法是使用Java 8：

int[] lowerThan500 = Arrays.stream(numbers).filter(i -> i < 500).toArray(); 

更少的代碼，錯誤更少。

或者：

long nbLessThan500 = Arrays.stream(numbers).filter(i -> i < 500).count();