String Concatenate +=

Question

I'm trying to debug this code that another developer created. I think the code is trying to create a string that's a query. The reason that I need to fix is is that if the value 'strSelectedProductIdentifier' has a ' character then it breaks a button and does not do any action.

Example:

 public void addIntoSelectedProduct()
{
    String query = 'SELECT ';
    set<String> setFields = new set<String>(); // set to check Product_Identifier__c field exist in fieldset or not
    for(Schema.FieldSetMember f : SObjectType.Product2.FieldSets.SL_ProductMgtTool.getFields()) {
        query += f.getFieldPath() + ', ';
        setFields.add(f.getFieldPath());
    }
    query += 'Family, ';
    //handled this issue for product identifier with single quote
    System.debug('Product identifier is::' + strSelectedProductIdentifier);
    strSelectedProductIdentifier = strSelectedProductIdentifier.contains('%%%%%%') ? strSelectedProductIdentifier.replace('%%%%%%', '\''):strSelectedProductIdentifier;
    System.debug('Product identifier is::' + strSelectedProductIdentifier);
    if(setFields.isEmpty())
        ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR, 'Please select a field in fieldset.'));
    else
    {    
        if(setFields.contains('Product_Identifier__c'))
            query += 'Id FROM Product2 WHERE isActive = true AND Product_Identifier__c =\''+strSelectedProductIdentifier+'\' ';
        else
            query += 'Id, Product_Identifier__c FROM Product2 WHERE isActive = true AND Product_Identifier__c =\''+strSelectedProductIdentifier+'\' ';

        //based on the select product, create a new wrapper
        lstProduct2Wrapper.add(new product2Wrapper(Database.Query(query), objOpp, strSelectedRetailer, strSelectedAU));
    }
}

My question is what does the += mean when it goes query +=. I know that if you do string + string then that concatenates the values together. I've never seen += together like that and I'm confused.

Answer 1

+=, and other related operators, are often called short-hand operators. They serve the role of reducing the amount of typing you have to do when you want to modify the same variable you're assigning to, which is incredibly common. In addition to +=, there are other things you can do as well:

Integer a = 100;

a /= 5; // Divide; a is now 20
a *= 5; // Multiply; a is now 100
a -= 6; // Subtract; a is now 94
a += 4; // Add; a is now 98

a ^= 33; // XOR; a is now 67
a &= 63; // AND; a is now 3
a |= 9; // OR; a is now 11
a <<= 1; // Shift-Left; a is now 22
a >>= 2; // Shift-Right; a is now 5
a = -1000000; // Used for the next step
a >>>= 2; // Unsigned-Bit-Shift-Right; a is now 1073491824

If you don't understand the last section, that's okay, as you'll rarely use them until you get to more advanced programming. You might want to read more about "Boolean algebra" if you're interested, though.

You can read more about operators here.

Answer 2

+= is an operand that basically mimics x = x +.

In this case, query += "aa" means query = query + a. In effect, you are adding the new value to the original.

This works as well for numbers. For example, a+=1 equals a = a + 1, thereby incrementing a by 1.