錯誤：Android上的java.lang.ArrayIndexOutOfBoundsException

Question

我有此代碼： indexOfChromosomes：48 indexOfGens：20 double截斷; double Crossover; double mutation; int Generation;

private Context context; 

int indexOfChromosomes; 
int indexOfGens; 
int gensNumber; 
int chromosomesNumber; 

public AdapterDB(int Bits, double Truncation, double Crossover, double Mutation, int Chromosomes, int Generation, Context ctx) 
{ 
    this.indexOfGens = Bits; 
    this.Truncation = Truncation; 
    this.Crossover = Crossover; 
    this.Mutation = Mutation; 
    this.indexOfChromosomes = Chromosomes; 
    this.Generation = Generation; 
    this.context = ctx; 
    DBHelper = new DatabaseHelper (context); 
} 

String [][] population = new String[indexOfChromosomes][indexOfGens]; 

    public void generateChromosome() 
{  
    for(chromosomesNumber = 0; chromosomesNumber < indexOfChromosomes ; chromosomesNumber++) 
    { 
        int o = 0; 
     for(gensNumber = 0; gensNumber < 12 ; gensNumber++) 
     { 
      Cursor l = db.rawQuery("SELECT _id, key_foodstuff, key_calorie, key_carbohydrate, key_fat, key_protein FROM (food INNER JOIN categories ON food.key_nocategory = categories.nocategories) WHERE key_type='primary' AND _id!=164 AND (key_carbohydrate!=0 OR key_protein!=0 OR key_fat!=0) ORDER BY RANDOM() LIMIT 1", null); 

      if((l.moveToFirst()) && (l!=null)) 
      { 
       if (o == indexOfGens) 
       { 
        gensNumber = 0; 
        sumOfCarbohydrateMor = 0; 
        sumOfFatMor = 0; 
        sumOfProteinMor = 0; 
        sumOfCalorieMor = 0; 
        o = 0; 
       } 

       population[chromosomesNumber][gensNumber] = l.getString(0); 
       morning_food[k] = l.getString(3); 
       sumOfCarbohydrateMor = sumOfCarbohydrateMor + Double.parseDouble(morning_food[k]); 
       morning_food[f] = l.getString(4); 
       sumOfFatMor = sumOfFatMor + Double.parseDouble(morning_food[f]); 
       morning_food[p] = l.getString(5); 
       sumOfProteinMor = sumOfProteinMor + Double.parseDouble(morning_food[p]); 
       morning_food[c] = l.getString(2); 
       sumOfCalorieMor = sumOfCalorieMor + Double.parseDouble(morning_food[c]); 
       if (((sumOfCarbohydrateMor >= (morning_car-(morning_car*0.2))) && (sumOfCarbohydrateMor <= morning_cal*1.1)) && ((sumOfProteinMor >= (morning_pro-(morning_pro*0.2))) && (sumOfProteinMor <= morning_pro*1.1)) && ((sumOfFatMor >= (morning_fat-(morning_fat*0.2))) && (sumOfFatMor <= morning_fat*1.1))) 
       //if((sumOfCarbohydrateMor > (morning_car*0.6)) && (sumOfProteinMor > (morning_pro*0.7)) && (sumOfFatMor > (morning_fat*0.8))) 
       { 
        Log.e("lala", "lalala"); 
        break; 
       } 

       if ((sumOfCarbohydrateMor > (morning_car*1.1)) || (sumOfProteinMor > (morning_pro*1.1)) || (sumOfFatMor > (morning_fat*1.1)) || (sumOfCalorieMor > (morning_cal*1.1)) 
       { 

        morning_food[k] = l.getString(3); 
        sumOfCarbohydrateMor = sumOfCarbohydrateMor - Double.parseDouble(morning_food[k]); 
        morning_food[f] = l.getString(4); 
        sumOfFatMor = sumOfFatMor - Double.parseDouble(morning_food[f]); 
        morning_food[p] = l.getString(5); 
        sumOfProteinMor = sumOfProteinMor - Double.parseDouble(morning_food[p]); 
        morning_food[c] = l.getString(2); 
        sumOfCalorieMor = sumOfCalorieMor - Double.parseDouble(morning_food[c]); 
        gensNumber--; 
        o++; 

       } 

      } 
     } 

，並錯誤行：48

錯誤說：java.lang.ArrayIndexOutOfBoundsException

什麼想法？ THXü

Answer 1

這是你的問題：

String [][] population = new String[indexOfChromosomes][indexOfGens]; 

出現這種情況外你的構造，因此您的構造函數之前執行，當indexOfChromosomes和indexOfGens都是仍爲0把初始化內您的構造函數。下面是顯示了同樣的問題一個簡單的例子：

public class Test { 
    private int size; 

    public Test(int size) { 
     this.size = size; 
    } 

    private String[] array = new String[size]; 

    public static void main(String[] args) { 
     Test t = new Test(5); 
     System.out.println(t.array.length); 
    } 
} 

和固定版本：

public class Test { 
    private int size; 
    private String[] array; 

    public Test(int size) { 
     this.size = size; 
     array = new String[size]; 
    } 


    public static void main(String[] args) { 
     Test t = new Test(5); 
     System.out.println(t.array.length); 
    } 
} 

注意，相對於構造函數的變量聲明的定位使得來執行流程沒有什麼區別。

編輯：至於爲什麼它現在循環永遠 - 在你的代碼中你有：

if (o == indexOfGens) 
{ 
    gensNumber = 0; 
    ... 
} 

將內環重置回（幾乎）開始（並不完全是開始，因爲gensNumber將在循環體的末尾增加，在下一次迭代開始之前）。

這並不完全清楚你想要做什麼，但我懷疑這沒有幫助。

我還鼓勵您使用當地變量儘可能 - 這是非常不尋常的使用實例變量作爲循環計數器，例如。

最後，我鼓勵你將你的大方法分解成更小的方法以提高可讀性。

Answer 2

嘗試設置

population = new String[indexOfChromosomes][indexOfGens]; 

您adapterDB內。

看起來當你初始化人口普查看人口，indexOfChromosomes和indexOfGens尚未初始化，所以要創建大小爲0的數組像這樣，當你調用

population[chromosomesNumber][gensNumber] 

你的java.lang。ArrayIndexOutOfBoundsException

Answer 3

這是因爲您在函數外定義了總體字符串，而沒有將indexOfChromosomes初始化爲48，將indexOfGens初始化爲20.嘗試在頂部定義總體並將其設置爲適配器中的新內容，在設置好後你的變量。就像這樣：

double Truncation; 
double Crossover; 
double Mutation; 
int Generation; 

private Context context; 

int indexOfChromosomes; 
int indexOfGens; 
int gensNumber; 
int chromosomesNumber; 

String [][] population; 

public AdapterDB(int Bits, double Truncation, double Crossover, double Mutation, int Chromosomes, int Generation, Context ctx) 
{ 
    this.indexOfGens = Bits; 
    this.Truncation = Truncation; 
    this.Crossover = Crossover; 
    this.Mutation = Mutation; 
    this.indexOfChromosomes = Chromosomes; 
    this.Generation = Generation; 
    this.context = ctx; 
    DBHelper = new DatabaseHelper (context); 

    //Create population after initializing variables. 
    population = new String[indexOfChromosomes][indexOfGens]; 
}