java - 只打印数组中 3 的倍数

Question

我正在尝试完成一个练习，其中我有一些任务，包括这个:只打印数组中 3 的倍数我必须使用小程序，但我不知道该怎么做。我试图在图形部分设置条件，但它返回一个不好的 0

public void init() {
  dataList = new int[17];
  int dataList[] = {2,4,6,9,5,4,5,7,12,15,21,32,45,5,6,7,12};

  for (int i = 0; i < dataList.length; i++) {
    //Compute the sum of the elements in the array.
    sum += dataList[i];
    //Compute the product of the elements in the array.
    product *= dataList[i];
    //Compute the frequency of the number 5 in the array
    if (dataList[i] == 5) {
      fiveCounter++;
    }
  }
}

public void paint(Graphics g) {
  g.drawString(("Sum of elements is: " + sum), 25, 25);
  g.drawString(("Product of elements is: " + product), 25, 50);
  g.drawString(("Number 5 is present " + fiveCounter + " times"), 25, 75);
  for (int i = 0; i < dataList.length; i++) {
    if ((dataList[i] % 3) == 0) {
      g.drawString((String.valueOf(dataList[i])), 25, 100);
    }
  }
}

在我尝试根据值的倍数 3 的计算创建新数组的另一次尝试中，程序没有启动，我得到 ArrayIndexOutOfBoundException

public void init() {
  dataList = new int[17];
  multiple3 = new int[mult3Counter];
  int dataList[] = {2,4,6,9,5,4,5,7,12,15,21,32,45,5,6,7,12};

  for (int i = 0; i < dataList.length; i++) {
    //Compute the sum of the elements in the array.
    sum += dataList[i];
    //Compute the product of the elements in the array.
    product *= dataList[i];
    //Compute the frequency of the number 5 in the array
    if (dataList[i] == 5) {
      fiveCounter++;
    }
    if ((dataList[i] % 3) == 0) {
      multiple3[i] = dataList[i];
      mult3Counter++;
    }
  }

public void paint(Graphics g) {
  g.drawString(("Sum of elements is: " + sum), 25, 25);
  g.drawString(("Product of elements is: " + product), 25, 50);
  g.drawString(("Number 5 is present " + fiveCounter + " times"), 25, 75);
  for (int i = 0; i < multiple3.length; i++) {
    g.drawString((String.valueOf(multiple3[i])), 25, 100);
  }
}

我该如何解决这个问题？

Answer 1

您不能对两个数组使用相同的计数器。使用两个不同的计数器。您不能使用 mult3Counter 作为数组 multiple3 的大小，因为它未初始化!因此，mult3Counter 默认为 0。因此，当您要使用任何索引访问 multiple3[] 时，它会给出 ArayIndexOutOfBoundsException

如果要知道3的倍数出现的次数，就得循环两次；

int mult3Counter = 0;
for (int i = 0; i < dataList.length; i++) {
  if ((dataList[i] % 3) == 0) {
    mult3Counter++;
  }
}

int j = 0;
int [] multiple3 = new int[mult3Counter];

for (i = 0; i < dataList.length; i++)
{
  if ((dataList[i] % 3) == 0)
  {
    multiple3[j++] = dataList[i];
  }
}

或者最好的方法是使用List(ArrayList)来添加3的倍数。

ArrayList<int> multiple3 = new ArrayList<>();

for (int i = 0; i < dataList.length; i++) {
  if ((dataList[i] % 3) == 0) {
    multiple3.add(dataList[i]);
  }
}

如果需要数组，后面可以转成数组。引用This Question