Java-数组大小未更新

Question

读取用户的整数，然后显示输入的数字列表和每个值的频率。输入的数量应在1-30之间变化，并且值接受0-9。

我的问题是，即使我将数组更改为int[] numbers = new int[numInputs];，它也始终默认为1。在第一个for循环期间，numInputs似乎被写为1，但即使更改了numInputs的值，它仍然上限为1。我确信我的逻辑是错误的，但我不确定在哪里。

public class Occurrence
{
public static void main(String[] args)
{
//variables
Scanner keyboard = new Scanner(System.in);
int numInputs = 1, temp;
int[] numbers = new int[31];
int[] count = new int[31];
boolean success = false;
//start of program
System.out.println("How many input values [max:30]?");
//while no valid input
while (!success)
{
try
{
numInputs = keyboard.nextInt(); //get a number
numInputChecker(numInputs);     //is it valid?
success = true;                 //ok
}
catch (Exception e)                 //else get a new number
{
keyboard.nextLine();
System.out.println("Whole numbers 1 through 30 only, please.");
}
}
//reset the loop checker
success = false;
//read numbers to fill that array
System.out.println("Enter " + numInputs + " numbers.");
for(int i = 0; i < numInputs; i++)     //from 0 to max number
{
while (!success)                   //while no valid number
{
try
{
numbers[i] = keyboard.nextInt();    //fill the current cell with a number
numberChecker(numbers[i]);          //is it valid?
success = true;                     //ok
}
catch (Exception e)                     //else get a new number
{
keyboard.nextLine();
System.out.println("Whole numbers 0 through 9 only, please.");
}
}
}
//take the input and count each use of element
for (int i = 0; i< numbers.length; i++)     //for 0 to max number
{
temp = numbers[i];  //get the current value of the cell
count[temp]++;      //add the use of that value to a new array's cell
}
for(int i = 0; i < count.length; i++)   //from 0 to 9 (expected)
{
if (count[i] > 0 && count[i] == 1)  //if cell not empty
{
System.out.println(i + " " + count[i]);  //print the current cell and how many times it was used
}
}
}
static void numInputChecker(int integer) throws Exception
{
if ((integer < 1) || (integer > 30))    //if 0 or negative, or if 31+
{
throw new Exception();              //say no
}
}
static void numberChecker(int integer) throws Exception
{
if ((integer < 0) || (integer > 9)) //if negative or 10+
{
throw new Exception();          //say no
}
}
}

Answer 1

逻辑在第二个循环中被破坏，因为成功变量不会在随后的while循环中重置。这样修复它很容易：

for (int i = 0; i < numInputs; i++)     //from 0 to max number
{
while (!success)                   //while no valid number
{
try {
numbers[i] = keyboard.nextInt();    //fill the current cell with a number
numberChecker(numbers[i]);          //is it valid?
success = true;                     //ok
} catch (Exception e)                     //else get a new number
{
keyboard.nextLine();
System.out.println("Whole numbers 0 through 9 only, please.");
}
}
success = false; // [amsilf]: That's the cycle reset
}

Answer 2

可能会发生java.util.NoSuchElementException并捕获处理块的错误。

在keyboard.nextInt()之前使用keyboard.hasNextInt()。

像这样！

try {
keyboard.hasNext(); // here!
numInputs = keyboard.nextInt(); //get a number
numInputChecker(numInputs);     //is it valid?
success = true;                 //ok
}
...

Answer 3

在最后一个for循环中应该是

for(int i = 0; i < count.length; i++)   //from 0 to 31(expected)
{
if (count[i] > 0)  //if cell not empty
{
System.out.println(i + " " + count[i]);  //print the current cell and how many times it was used
}
}