Making a method for swaping two int's position within an arraylist

Question

Anyone give me any insight as why the following snippet of code gives a cannot find symbol error, this swap() should be used as when given an array list name it will swap the contents of index location 1 with location 2

Cheers!

public static void swap(String swapArray, int location1, int location2) {
    int tempswap1 = swapArray.get(location1);
    int tempswap2 = swapArray.get(location2);
    swapArray.set(location1)=tempswap2;
    swapArray.set(location2)=tempswap1;
}

`swapArray` is not an `ArrayList`, it is a `String`. In Java, `String`s are immutable (cannot be modified). — robbie_c, Oct 15 '13 at 12:07

score 1 · Answer 1 · edited May 23 '17 at 10:25

1

Cause for error:

swapArray.set(location1)

swapArray.get(location1)

Since swapArray is a String type, there in no set method and even get method in String class.

Possible resolution:

If I'm not wrong, swapArray should be List type. Please check and as a side note use an IDE like Eclipse which saves you lot of time.

Might useful further :

Arraylist swap elements

Update:

    public static void swap(List swapArray, int location1, int location2) {
-------------------------------^
        int tempswap1 = swapArray.get(location1);
        int tempswap2 = swapArray.get(location2);
        swapArray.set(location1,tempswap2);
        swapArray.set(location2,tempswap1);
    }

Assuming you are passing a list to swap method.

edited May 23 '17 at 10:25

Community

1
1

answered Oct 15 '13 at 12:05

Suresh Atta

120,458
37
198
307

The swapArray is used to enter the name of arraylist which i would like to swap, as there is multiple, how would use the users data with out using a string to achieve this, Thanks! – Dmcdaid Oct 15 '13 at 12:12
@DavidMcDaid Your method signature is wrong, updated the post. – Suresh Atta Oct 15 '13 at 12:17

Rahul · Answer 2 · 2013-10-15T12:21:09.720

Assuming the swapArray is of type list as mentioned in your question title, you need to swap the values like this

swapArray.set(location1, tempswap2); // Set the location1 with value2
swapArray.set(location2, tempswap1); // Set the location2 with value1

The error is because of swapArray.set(location1)=tempswap2;. The left hand side is a method call(set()) which returns a value and you are trying to assign another value to a value, which is illegal. You need to have a variable on the LHS of the assignment operator.

Also, this should be/have been the actual method signature

public static void swap(List<Integer> swapArray, int location1, int location2)
                        ^^^^^^^^^^^^^ - This is the type of the object you're passing. You needn't give the name of that object as such.

Side Note: Always remember to copy/paste the code from the IDE, instead of manually typing it here, as you tend to make typos and syntax errors.

score 0 · Answer 3 · answered Oct 15 '13 at 12:11

0

There is a trick you can use here

public static <T> void swap(List<T> list, int pos1, int pos2) {
    list.set(pos1, list.set(pos2, list.get(pos1)));
}

answered Oct 15 '13 at 12:11

Peter Lawrey

525,659
79
751
1,130

score 0 · Answer 4 · edited May 23 '17 at 12:10

0

String are immutable in Java. You can't change them. You need to create a new string with the character replaced. Check this thread: Replace a character at a specific index in a string?

edited May 23 '17 at 12:10

Community

1
1

answered Oct 15 '13 at 12:16

drop.in.ocean

298
2
9

Terry · Answer 5 · 2013-10-15T12:36:29.970

I like Peter's answer better. But if you were just putting your Strings in a collection for purposes of calling setters (that don't exist anyway) you can do it all with native code.

Keep in mind that if you're doing a lot of String manipulation you should use a StringBuffer if you need thread safety or a StringBuilder if your program is not multi-threaded. Because as mentioned Strings are actually immutable - meaning every time you change one you are actually destroying the old object and creating a new one.

This code would need to be a little smarter if the starting point (e.g. loc1) could be offset 0, but the general idea for native String manipulation is:

String x = a.substring(loc1,loc1+1);
String y = b.substring(loc2,loc2+1);
a = a.substring(0, loc1) + y + a.substring(loc1);
b = b.substring(0,loc2) + x + b.substring(loc2);

Making a method for swaping two int's position within an arraylist

5 Answers5