Getting an error of out of bound in main function

#1

public static void main(String[] args) {
// TODO Auto-generated method stub
int[] a = null;// declaring the array
a = new int[5];// blocking the space
a[0] = 1;
a[1] = 5;
a[2] = 10;
a[3] = 15;
a[4] = 20;
int j;
for(int i=0;i<=4;i++) {
for(j=4;j>=0;j++) {
int b =a[i];
a[i]= a[j];
a[j] = b;
System.out.println(a[i]);
System.out.println(a[j]);
}
}
}
}

#2

@rishabh.chhabra10,
In:

for(int i=0;i<=4;i++) {
for(j=4;j>=0;j++) {

You have used j++. At the start j = 4, after increment it becomes 5. Hence out of bounds.

Use j-- instead of j++

#3

still not getting the right answer

#4

i am not able to understand swap from this video too confusing, pls explain

#5

@rishabh.chhabra10,
Instead of swapping the elements you are restoring them in the same order as well.

Initial array: 1, 5 , 10 , 15, 20

Now in the for loop:
when i = 0,
and we start from j = 4:

b = a[0] = 1
a[0] = a[4] and a[4] is 20. Hence, a[0] = 20
a[4] = 1
Array becomes: 20, 5, 10, 15, 1

Now when j=3:
b = a[0] = 20
a[0] = a[3] and a[3] is 15. Hence, a[0] = 15
a[3] = 20
Array becomes: 15, 5, 10, 20, 1

And so on. But if you stop and loop, at j=3, the element is not swapped with a[1], instead it is swapped with a[0].

#6

@rishabh.chhabra10,

In the swap function we pass arr, i, j. We swap index i and j. Now in the swap method we pass reference of the array and swap index i and j. As soon as it returns back to the main method, the changes are made in the original array.
Example:
Array a: 1 2 3 4 5
Swap (a,0,2)
Now before entering swap function a will be: 1 2 3 4 5
After swap function a will be : 3 2 1 4 5
The changes will be made in the current array.

#7

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