Setting value in Java array returns error

Question

This method is supposed to set a value in an array, given its index. The error is an ArrayIndexOutOfBoundsException, which occurs on the line:

 GrowingArray [index] = value;

However, I've done some research and using array [index] = value seems to be a legitimate way to set a value in an array. A pointer in the right direction would be helpful.

public void set (int index, int value) {
  if (index <= GrowingArray.length) {
    GrowingArray[index] = value;
  } else {
    int [] destination = new int [12/10*GrowingArray.length];
    destination [index] = value;
    System.arraycopy(destination, 0, GrowingArray, 0, destination.length);
  }
}

Jack · Accepted Answer · 2016-06-15 04:03:49Z

1

Java arrays have 0 based indices (like 99% of things in computer science), so checking <= (instead that < ) will allow, for example the index 4 for an array of size 4, which will end out of bonds.

if (index <= GrowingArray.length){
  GrowingArray[index] = value;

In addition 12/10 is an integer division which yields 1, if you want to increase capacity by 20% you should use float values, eg:

int newCapacity = (int)(oldCapacity*1.2f);

answered Jun 15, 2016 at 4:03

Jack

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1 Comment

pianos Over a year ago

Thank you! I didn't realize that <= allowed my array check to go out of bounds. I changed it to < as you said to, and the error is gone.

Ming · Accepted Answer · 2016-06-15 04:10:00Z

1

in java array's index start with 0,

so when index == GrowingArray.length, the max index of GrowingArray is [index - 1]

what about try to change

if (index <= GrowingArray.length)

to

if (index < GrowingArray.length){

answered Jun 15, 2016 at 4:10

Ming

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