How to access elements in an array from another method?

Question

I'm trying to implement an algorithm in one method that takes in two lists of type studentlist and I need to access the array from the constructor method, studentList to get the size and the student numbers to compare between lists.

e.g.

for (int i = 0; i < L1.studentID.length-1; i++) {
    for (int j = 0; j < L2.studentID.length-1; j++) {
        if (L1.studentID[i] = L2.studentID[j]) {
            num++; }}}

Most of the constructor, and not including the 2nd one for accessing lists in a file instead of randomly generated:

studentID=new int[size];
boolean[] usedID=new boolean[IDrange];
for (int i=0;i<IDrange;i++) usedID[i]=false;
for (int i=0;i<size;i++) {
    int t;
    do {
    t=(int)(Math.random()*IDrange);
    } while (usedID[t]);
    usedID[t]=true;
    studentID[i]=t; }

Size (list.studentID.length or I could have used list.numberOfStudents which is built in) seems fine, but I'm having trouble with getting the elements of the array themselves. I figure I could just do list.studentID[i] but I get a 'type mismatch: cannot convert from int to boolean'.

Any ideas?

why not L1.studentID[i] == L2.studentID[j]? //double '='

koponk
– koponk

2013-01-25 15:11:56 +00:00
Commented Jan 25, 2013 at 15:11 — koponk
– koponk, Commented Jan 25, 2013 at 15:11

fmsf · Accepted Answer · 2013-01-25 15:10:25Z

2

Your issue is here:

if (L1.studentID[i] = L2.studentID[j])

You are making an attribution of L2.studentID[j] to L1.studentID[i] and then passing the value of L1.studentID[i] to the if

The if in java expects explicittly a boolean value.

You either want to do:

if (L1.studentID[i] == L2.studentID[j])

or

if ((L1.studentID[i] = L2.studentID[j])!=0)

The code you currently have is the same as doing:

L1.studentID[i] = L2.studentID[j];
if (L1.studentID[i]){  <-- this won't work because L1.studentID[i] is an int and the if expects a boolean
...

answered Jan 25, 2013 at 15:10

fmsf

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1 Comment

Adam Over a year ago

Oh yea, completely forgot I had to do that! Thanks everyone, thought it had something to do with the boolean in the constructor or something.

Rafael Companhoni · Accepted Answer · 2013-01-25 15:11:08Z

2

You should compare them like this

if (L1.studentID[i] == L2.studentID[j])

Otherwise you're doing an attribution of L2 to L1.

answered Jan 25, 2013 at 15:11

Rafael Companhoni

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Comments

davioooh · Accepted Answer · 2013-01-25 15:16:08Z

2

'type mismatch: cannot convert from int to boolean'

You are getting an int because you are doing an assignment: = operator. To compare two integers you need to use == operator.

Try with

if (L1.studentID[i] == L2.studentID[j]) {

and you'll get a boolean.

edited Jan 25, 2013 at 15:16

answered Jan 25, 2013 at 15:10

davioooh

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