System.NullPointerException: Attempt to de-reference a null object

Question

I was new to salesforce. I was try trying to update that account record name belong to me. I am getting System.NullPointerException: Attempt to de-reference a null object could some can help me here is my class

public class MyController {

private final Account account;

public MyController() {
     list<Account> account = [SELECT Id, Name, Site FROM Account WHERE Id = :ApexPages.currentPage().getParameters().get('id')];
}

public Account getAccount() {
    return account;
}

public PageReference save() {
    update account;
    return null;
}
}

Answer 1

Your private variable account isn't being assigned a value anywhere, so it's null when you try and update it in the save() method:

private final Account account;

public MyController() {
    // this creates a variable called account local to this method, which is not visible elsewhere
     list<Account> account = [SELECT Id, Name, Site FROM Account WHERE Id = :ApexPages.currentPage().getParameters().get('id')];
}

You could try this:

public MyController() {
    // this creates a variable called account local to this method, which is not visible elsewhere
     list<Account> account = [SELECT Id, Name, Site FROM Account WHERE Id = :ApexPages.currentPage().getParameters().get('id')];
     this.account = account[0];
}

But personally I'd avoid using the same variable name (other than for things like loop indices) inside a single class, it's a recipe for confusion like this. Rename the list something else such as accountList. I also avoid naming variables with the names of objects for the same reasons, renaming account to acct or theAccount might not be a bad idea.

Answer 2

Just to add on top of the existing solution its always advisable to check the null values for example we can do below.

public Account getAccount() {
    if(account != null)   //Check if account has any value to return.
        return account;
    else
        return null;
}

public PageReference save() 
{
    if(account != null)   //Check if account has any value to update.
          update account;
    return null;
}