Swapping Values in an array - Java

[CalebTheEternal]

I am in an AP Computer Science class at school and we are learning Java and I'm not sure how to do this.

I need to "Swap the values at positions i and j in the array"

 

That is all of the info I have. 

 

My teacher is a Math teacher and can't explain this to save his life. 

 

Thanks for the help.

[madknight3]

Do you know how to get a value from an array?

Do you know how to modify a value in an array?

 

If so you're most of the way there.

[CalebTheEternal]

Do you know how to get a value from an array?

Do you know how to modify a value in an array?

 

If so you're most of the way there.

Not at all. Care to explain how? 

[squirrl]

Not at all. Care to explain how? 

 

 

x is your array

to get the value at i

x

 

to modify a value

 

x = 2

 

There, you're most of the way there.

[Nineshadow]

Let's first look in how to swap two values :

int a = <value>;int b = <value>;int temp = a;a = b;b = temp;

Then you just do that with the elements at the given positions.

 

void swap(int *v, int i , int j){    int temp = v[i];    v[i] = v[j];    v[j] = temp;}

[Philosobyte]

An array is like a list of values. So, let's say you have a String array called ar, with two values, "hello" and "there", like so:

String[] ar = {"hello", "there"};

In order to swap "hello" (in position 0) and "there" (in position 1), you need to obtain the value from the first position and assign it to the second position, and take the value from the second position and assign it to the first position. In this case that would mean taking "hello" and using it to overwrite "there", and then taking "there" and using it to overwrite "hello".  Like this:

String[] ar = {"hello", "there"};ar[1] = ar[0];ar[0] = ar[1];

But there's a problem. if you overwrite one of the values, how are you going to use the overwritten value which no longer exists in the array? Try to find the solution to that yourself. 

 

Edit: I sympathize with your situation. When I took AP Computer Science, the actual teacher left the school two weeks before school began to be a principal at another school, so we had a year-long substitute who was a biology major and knew little about coding. Our school ended up paying for an online class, with online materials and an online teacher. 80% of the students failed anyway. 

Edited November 5, 2015 by Raymondbl

[BlueDragon]

In this method we are basically swapping two positions in the array.

public static void swap(String[] arr, int x, int y){		//We have to store value in the index of x because we are about to over right thatString temp = arr[x];//We then set what is in the array at position x to be what is in the array at position yarr[x] = arr[y];//Finally we then have to set what is in position y to be temp.arr[y] = temp;}