List Index out of Bounds: -1

Question

I know List Index out of Bounds: positive num but I am getting List Index out of Bounds: -1 error. What does this mean ?

if(pnlNewYearsd.size() > 0) {
    startYear = pnlNewYearsd.get(0);
} else{
    if(startYear == '') {
    // getting error in below line 
    startYear = **temp_hop_id_list[(temp_hop_id_list.size()/2)-1].Year__c;**
    } else {
    startYear = temp_hop_id_list[temp_hop_id_list.size()-1].Year__c;
    }                      
}

Answer 1

You are running into this issue based on the size of your temp_hop_id_list. At the point of performing the division on list size your list size appears to be <= 1.

Here is some logic I have created to illustrate how you would recieve a List Index Out Of Bounds: -1 error.

List<Contact> emptyCons = new List<Contact>();

if(emptyCons.size() > 0) {
    system.debug('Woohoo');
} else {
    system.debug('Below is a List Index Out Of Bounds -1 error.');
    system.debug((cons.size()/2)-1);
}

Changes needed to your logic:

if(pnlNewYearsd.size() > 0) {
    startYear = pnlNewYearsd.get(0);
} else {
    if (temp_hop_id_list.size() >= 2) {
        startYear = startYear == '' ? temp_hop_id_list[(temp_hop_id_list.size()/2)-1].Year__c : temp_hop_id_list[temp_hop_id_list.size()-1].Year__c;
    } else {
        // Exception Handling
    }                    
}

Here you are making sure your list size is greater or equal than 2 to allow the division only ever end with a result of 0 or more.

I have also cleaned up all the if/else statements and used a ternary operator.

Answer 2

It means exactly what it says: you are trying to index the array at element -1. Caused by the expression between [ and ], meaning that temp_hop_id_list.size()/2 has a value of 0.

Answer 3

I think temp_hop_id_list.size() is of size 0 or 1 . You can add condition to handle this error.

if(think temp_hop_id_list.size()>=2) {
    startYear = temp_hop_id_list[(temp_hop_id_list.size()/2)-1].Year__c;
    } else {
    startYear = temp_hop_id_list[temp_hop_id_list.size()-1].Year__c;
    }  
}