为什么会出现“分配的左侧必须是变量”？

Question

I'm making a "dog register" where you can save information about dogs and bid on dogs up for auction etc. I am a beginner and was recently told that array list should be private, this information got me in some trouble.

I got a class named Auction where you can store bids, I made a get method in this class to use in the main class. It works on every line except one in my method where you can delete a user.

private void deleteUser()
{
    System.out.println("Enter the name of the user: ");
    String name = input.nextLine().toLowerCase().trim();

    User deleteUser = getUser(name);
    while (name.isEmpty()) {
        System.out.println("Error. Enter the name of the user: ");
        name = input.nextLine().toLowerCase().trim();

        deleteUser = getUser(name);
    }

    if (deleteUser == null) {
        userException();
        return;
    }

    for (Auction a : auctionRegister) {
        ArrayList<Bid> bids = new ArrayList<>();
        for (Bid b : a.getBidList()) {
            if (b.getUser() != deleteUser) {
                bids.add(b);
            }
        }
        a.getBidList() = bids;
    }

    if (deleteUser.getDogList() != null) {

        for (Dog dog : deleteUser.getDogList()) {
            dogRegister.remove(dog);
        }
    }

    userRegister.remove(deleteUser);
    System.out.println("User " + deleteUser.getUserName() + " is removed");
}

I get the error message on this line("The left-hand side of an assignment must be a variable"):

a.getBidList() = bids;

Everything worked when i had the array list public so my question is, how do i solve this?

Answer 1

Java has 2 varieties of 'buckets' in which to store information. One variety is a variable , the other is a constant . Both varieties let you look in the bucket to see the contents. A variable also allows you to you replace the current contents of the bucket.

Your syntax , a.setBidList() is a method call, which is constant. You can read from it but you can't assign a new value to it. Since you have it on the left side of an assignment statement, you are asking Java to do something it can't do.