删除Java中的数组值将返回OutOfBoundsException

Question

I am a computer science student in high school, and I was given a project where I have to create a program that can add the values of an integer array, count the number of values contained in the array, and remove every instance of a value in that array.

Here is the code, separated into three methods for each function described above:

import java.lang.System;
import java.lang.Math;
import java.util.Arrays;

public class ArrayFunHouse
{
//instance variables and constructors could be used, but are not really needed

//getSum() will return the sum of the numbers from start to stop, not including stop
public static int getSum(int[] numArray, int start, int stop)
{
    int count = start;
    int output = 0;
    while(count<=stop)
    {
        output = output + numArray[count];
        count++;
    }
    return output;
}

//getCount() will return number of times val is present
public static int getCount(int[] numArray, int val)
{
    int x = 0;
    int count = 0;
    while(x<numArray.length)
    {
        if(val==numArray[x])
            count++;
        x++;
    }
    return count;
}

public static int[] removeVal(int[] numArray, int val)
{
    int[] newArray = new int[ numArray.length - getCount(numArray, val) ];
    int x = 0;
    for(int position = 0; position < numArray.length; position++)
    {
        x = numArray[position];
        if(x!=val)
        {
            newArray[position] = numArray[position];
        }
    }
    return newArray;
}
}

And here is the runner designed to execute the code, including the sample data we were instructed to use:

import java.util.Arrays;

public class ArrayFunHouseRunner
{
public static void main( String args[] )
{
    int[] one = {7, 4, 10, 0, 1, 7, 6, 5, 3, 2, 9, 7};

    ArrayFunHouse test = new ArrayFunHouse();

    System.out.println(Arrays.toString(one));
    System.out.println("sum of spots 3-6  =  " + ArrayFunHouse.getSum(one,3,6));
    System.out.println("sum of spots 2-9  =  " + ArrayFunHouse.getSum(one,2,9));
    System.out.println("# of 4s  =  " + ArrayFunHouse.getCount(one,4));
    System.out.println("# of 9s  =  " + ArrayFunHouse.getCount(one,9));
    System.out.println("# of 7s  =  " + ArrayFunHouse.getCount(one,7));
    System.out.println("new array with all 7s removed  =  " + test.removeVal(one,7));
    System.out.println("# of 7s  =  " + ArrayFunHouse.getCount(ArrayFunHouse.removeVal(one,7),7));

    int[] two = {4,2,3,4,6,7,8,9,0,10,0,1,7,6,5,3,2,9,9,8,7};

    //add test cases


}
}

When I run the code, the following is output:

[7, 4, 10, 0, 1, 7, 6, 5, 3, 2, 9, 7]
sum of spots 3-6  =  14
sum of spots 2-9  =  34
# of 4s  =  1
# of 9s  =  1
# of 7s  =  3
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 9
at ArrayFunHouse.removeVal(ArrayFunHouse.java:49)
at ArrayFunHouseRunner.main(ArrayFunHouseRunner.java:21)

Process completed.

As shown above, the code runs smoothly until it reaches the third method. What do I need to fix in order to get the code to run smoothly, as indicated by the error message?

Answer 1

In your removeVal function you are trying to set the index of the new array as the same index it had in the old array. As arrays get smaller, it can't place key 9 in an 8 item array.

Change it to this:

 int newPosition = 0;// outside of loop

    x = numArray[position];

    if(x!=val)
    {
        newArray[newPosition] = numArray[position];
        newPosition++;
    }

Answer 2

for(int position = 0; position < numArray.length; position++)
{
    x = numArray[position];
    if(x!=val)
    {
        newArray[position] = numArray[position];
    }
}

You can't use position to access both the target array and the source array. You need two variables, one of which isn't incremented if x == val .

Answer 3

I think it's because of this line: newArray[position] = numArray[position]; . Since newArray is shorter than numArray , numArray will have position indices that are out of bounds for numArray . You'd probably want two position values, say "newArPos" and "numArPos", and you don't increment "newArPos" if you're excluding a value.

Answer 4

In your removeVal method you create a new array that is smaller then the original one. But in your for loop you loop through a number of times equal to the original larger array. Make sure in your loop you don't access the new smaller array in a spot that only exists in the original array.